Army Vietnam Vehicle Recovery Operations

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Copy T FM 20-22DEPARTMENT OF THE ARMY FIELD MANUAL

VEHICLE RECOVERYOPERATIONS

HEADQUARTERS, DEPARTMENT OF THE ARMYOCTOBER 1962

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FM 20-22FIELD MANUAL HEADQUARTERS,

DEPARTMENT OF THE ARMYNo. 20-22 WASHINGTON 25, D.C., 31 October 1962

VEHICLE RECOVERY OPERATIONS

Paragraphs PageCHAPTER 1. INTRODUCTION_______-__ 1-3 32. FUNDAMENTALS OF

RECOVERYSection I. Basic principles ___________ 4-7 6II. Sources of power -_________-10 21III. Resistance ________________ 11-17 29

CHAPTER 3. RIGGING FORRECOVERYSection I. Distribution of effort and 18-21 36resistance.II. Rope and chain____________. 22-24 39III. Anchors_____________-_____ 25-27 41

IV. Recovery procedures________ 28-35 49V. Recovery techniques________ 36, 37 54VI. Safety__-___________-_____ 38-40 65

CHAiTER 4. FIELD EXPEDIENTS____ 41-92 715. VEHICLE RECOVERY

Section I. Similar vehicles ______-____- 93-100 130II. Special purpose vehicles ___.101-111 140

APPENDIX. REFERENCES --__-----_---------- 159INDEX -___________-_______-_---____-___---------- 160

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CHAPTER 1INTRODUCTION

1. PurposeThis manual provides the necessary informationand guidance for troops of all branches of the

Army to recover vehicles and equipment that havebecome disabled, including disability that may re-sult from the effects of terrain, enemy action, ormechanical malfunction.2. Scope

a. This manual contains formulas for use infield recovery operations and, in some instances,brief background material on which the formulasare based. It covers the application of rigging andsafety precautions to be observed in vehicle re-covery, expedient repairs, and operation of gen-eral and special purpose vehicles and equipmentused to keep vehicles operational. In certain in-stances, it may be necessary to combine two ormore of the principles given to accomplish aspecific recovery. The material presented is appli-cable, without modification, to both nuclear andnonnuclear warfare.

b. Users of this manual are encouraged to sub-mit recommended changes or comments to im-AGO 6473C 3


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prove the manual. Comments should be keyed tothe specific page, paragraph, and line of the textin which the change is recommended. Reasonsshould be provided for each comment to insureunderstanding and complete evaluation. Com-ments should be forwarded direct to U.S. ArmyArmor School.3. Definitions

In recovery, certain terms are common to allbranches. These terms are defined below as theywill be used throughout this text. When a terminvolves equipment, the equipment will be de-scribed and, if necessary, illustrated as it is intro-duced in the text.

a. Effort-an active force as distinguished frompassive resistance. Effort usually expresses asingle action rather than a continuous activity.Effort is required to start movement, but effortmay be made with no movement resulting if theobject to be moved is too heavy.

b. Force-theactive energy or physical strengththat is used to produce or modify motion. There-fore, after effort is exerted to start movement,some force is required to continue the action.Force includes the accomplishment of movement.

Note. There is only a fine line of distinction betweenforce and effort, and in some instances they may be usedinterchangeably. Force produces a result; effort may not.

c. Power-therate of transfer to energy. Poweris the product of force and distance divided bytime. Power would be used to move a weight4 AGO 6473C


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time (f below).d. Resistance-any opposing action that tendsto prevent motion. Resistance is usually con-

sidered constant in nature but can easily beaffected by its surroundings. Terrain providesresistance to movement of a vehicle, the degree ofresistance depending on the type of terrain andits condition. On a level surface, the resistancewill change materially as a vehicle moves fromhard surface to sand and to mud. On a grade,movement downhill is opposed by less resistancethan in movement uphill.

e. Strength-ability to resist force, or thecapability of a body to endure the application offorce without breaking or yielding. A rope hasstrength, according to its size and material, toendure the application of a certain amount of forcewithout breaking.

f. Work-the product of force and the distancethrough which the force acts. If a resistance isovercome and an object is moved from one placeto another, work has been performed.

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CHAPTER 2FUNDAMENTALS OF RECOVERY

Section I. BASIC PRINCIPLES4. Effort and Resistance

The application of effort to overcome a resist-ance has been a challenge to man since the begin-ning of civilization. Great strides have been madein overcoming resistances encountered in everydaylife. Today's routine acts in overcoming resistancewere yesterday's feats, and not too many yearsago, these feats were considered impossible. Theenergy released by the burning of a small amountof gasoline in an engine to provide the effort re-quired to move at high speed an automobile weigh-ing more than a ton is considered commonplace.Without the engine to drive it, the automobile,when on level surface, resists movement to thepoint where one man has difficulty pushing it,except for a short distance. If it becomes necessaryto push the car up even a short incline, the resist-ance is too great for one man to overcome. Theman would exert effort but would not overcomethe resistance to movement. The resistance wouldbe overcome if the man could increase his effort orif he could get additional men to help push. Hecan easily move the car, of course, if he starts the6 AGO 6473C


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engine and makes use of the mechanical devicesavailable within the automobile.5. Mechanical Advantage

The devices built into an automobile providemechanical advantage. Mechanical advantage isthe ability to use a small force, moved through along distance, to move a large resistance (object)a short distance. In an automobile, many applica-tions are made of mechanical advantage betweenthe piston in the engine and the wheels on theroad. But there are more common applicationsduring which everyday work is performed that arebeyond our strength unless some device is used togive assistance. A can opener is used to open cans;by moving the handle through a large arc, a rela-tively small cut is made in the can lid. We wouldnot be able to open a can without this assistance.A wrench is used to tighten a nut; by moving thewrench through a large arc, the resistance of thethreads is overcome. During World War II, theMissouri, a 34,000-ton battleship, was uprighted atPearl Harbor by use of twenty-six 5-horsepowerelectric motors working through a series of ropesand pulleys. All of these examples prove the worthof mechanical advantage.6. Lever

Mechanical advantage may be gained throughthe use of the principle of the lever. In each in-stance cited in paragraph 5, the principle of thelever was used. Probably the simplest form oflever is a rigid bar, free to turn on a fixed pivotAGO 6473C 7


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called a fulcrum. When an effort is exerted on oneend of the bar, the bar has a tendency to rotatearound the fulcrum. When a resistance is appliedto the other end of the bar, the resistance opposesthe effort and tends to cause the bar to operate inthe opposite direction. That part of the bar be-tween the point of application of effort and thefulcrum is called the effort arm or E; that part ofthe bar from the fulcrum to the center of resist-ance is called the resistance arm or R. A simplelever is illustrated in figure 1.

E t R

Figure 1. A simple Iever.There are several ways the mechanical advan-tage of the lever may be determined. From figure2, it will be noted that the work performed is thesame on both sides of the fulcrum. Five poundsof effort applied through a 4-foot arm equals 20pounds-feet; 10 pounds of resistance times 2 feetof arm equals 20 pounds-feet. It is equally truethat the distance B times 5 (pounds) would equaldistance A times 10 (pounds). Arm E (effort) istwice as long as arm R (resistance); the distanceB is twice as great as distance A. Although thework performed is the same, the result is just the8 AGO 6473C


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reverse; a small effort (5 pounds) moved an objectof resistance twice its weight (10 pounds). Thismakes the advantage gained 2 to 1. Mechanicaladvantage is always expressed as a ratio or thevalue of one item as related to another like item.So, the mechanical advantage can be figured as therelative lengths of the arms of the lever, or theamount of resistance moved in relation to the forceapplied. This remains true as long as friction doesnot cause a loss in the efficiency of the mechanism.Friction will be discussed separately in paragraph15.

a. Levers are divided into classes. The class ofa lever is determined by the location of thefulcrum.

EFFORT ARM (E) 4 FEET }

EFFORT BRESISTANCE ARM (R) = 2 FEET

f~ ? ~ FULCRUM

RESISTANCE

Figre 2. First-class lever.

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(1) A first-class lever has the fulcrum be-tween the effort and the resistance asillustrated in figure 1. Examples of first-class levers are scissors and pliers.(2) A second-class lever has the point of re-sistance between the fulcrum and theeffort. A second-class lever is illustratedin figure 3. A wheelbarrow is a goodexample of a second-class lever.

b. The principle of the lever is used in manyways that we are familiar with but may havenever recognized as such. Some of these ways areused in gears, in most machinery, in the elevator,in the winch, and in many other pieces of equip-ment.7. Tackle

Tackle is a combination of ropes and blocks usedto gain mechanical advantage. Tackle uses the

E=5 LB.4 FT. loF

2 FT.

10 LB.Figure 3. Second-class lever.

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principle of the lever in such a manner that anyeffort exerted will move a greater resistance.a. A block consists of a shell or frame in which

is mounted one or more grooved pulleys calledsheaves. The sheaves are mounted on a pin that issupported by the shell. The shell also has a meansof fastening the block in the tackle. The mostfrequently used fastening is a hook; however, theblock may be equipped with a becket (a metalloop) in addition to the hook, especially if it is de-signed to be used with fiber rope. Types of blocksmost commonly used in the military service areillustrated in figure 4.

A-Conventional blockFigure 4. Types of blocks.

A block is described by its type, the kind of ropewith which it is intended to be used, the numberof sheaves, the length of the shell in inches, thediameter of the groove, and its capacity. Blockswith 1, 2, or 3 sheaves are called single, double, orAGO 6473C 11


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HOOK

"t LOCKA,CABLE

' - SHEAVE

B-Snatch lockFigure4-Continued.

triple. They are also identified by features of theirconstruction and by the manner in which they areused in rigging. A conventional block, (A, fig. 4)is used mostly with fiber rope that must be reevedor threaded to be used. The block illustrated at Bis a snatch-type block. The snatch block, some-times called a gate block, is constructed so theshell opens at the base to admit a cable withoutreeving. The snatch block can be identified by the12 AGO 6473C


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hinge and lock on its side. It is generally usedwith wire rope or cable with fittings on the endthat will not permit them to be threaded, as a fiberrope. The complete name of a block might be listedas "block, snatch, wire rope, single, 12-inch sheave,11/ 4-inch diameter rope, 90-ton." From the namewe know that it is a snatch block with one 12-inchsheave grooved to fit a ll/,-inch rope, and witha capacity to support a 90-ton load. Only the sizerope for which the sheave was grooved should beused with a block. If a smaller rope is used, it hasa tendency to flatten out in the groove. If a largerrope is used, it will not go down into the groovecompletely and the edge of the groove may cut thestrands of the rope. In either case, the rope willbe damaged.

b. Blocks are classified as to their use in therigging.(1) When a block is fastened to a stationary

object, it is called a fixed block or leadingblock. A fixed block permits a change indirection of the rope but does not affectmechanical advantage (fig. 5).

(2) A running block or traveling block isfastened to the object to be moved andmoves with the object. The runningblock will produce a mechanical advan-tage (fig. 6).(3) An exception is made to the general rulesstated in (1) and (2) above when thesource of power is a part of the objectto be moved. For example, when the cable

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R F E EFFORT100 LB. 100 LB. 100 LB 100 LB.

Figure 5. The sheave as a first-class lever.

from a truck winch is passed through ablock and the end of the cable is returnedand fastened to the truck, the block willoffer mechanical advantage.

c. Any block, in effect, is a lever. A block per-forms the function of the lever more efficiently insome ways than the bar illustrated in figure 1, be-cause instead of the necessity of positioning thebar each time it moves through its arc, the sheaveoffers a continuous lever action. A block, in effect,becomes a spinning lever (fig. 7). One disadvan-tage of the block, however, is that the sheave rollson an axle (the pin) and friction is created be-tween the sheave and its axle (par. 15).14 AGO 6473C


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(1) A fixed block is generally a first-classlever (fig. 8). This is so because thecable enters one side of the block from asource of power that creates the effort,passes around the block, and returns tothe resistance. The pin on which thesheave revolves becomes the fulcrum.From paragraph 6, it was learned thatthe mechanical advantage could be deter-mined by the relative lengths of the Eand R arms. Since the radius is the sameon one side as on the other, the ratio is1 to 1 and no advantage is gained.

(2) With a running block, the action is some-what different. The sheave is still reevedin the same manner; however, the ful-crum moves from the center to the edgeof the sheave. The point of resistance isnow the pin in the center of the sheaveand the effort is placed on the other edgeof the sheave. The sheave becomes asecond-class lever as illustrated in figure9.

d. The other item used in the tackle is rope or,in some instances, chain. Rope may be made offiber or steel wire. Rope has strength throughoutits length; it resists being pulled apart. It hasvery little resistance to bending however, and isconsidered flexible. Rope is used for manypurposes and is, by far, the most important singleitem used in recovery. When wire rope is usedon a winch, the rope is generally called a cable.16 AGO 6473C


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LOAD

LOAD

Figure 8. Mechanical advantage: 1 to 1.

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i ii LOAD

Figure 9. Mechanical advantage: 2 to 1.

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Rope is discussed in detail in TM 5-725. Rope, asit is used in recovery, is discussed in chapter 3,this manual.

e. Whenever the resistance to be moved isgreater than the effort available, mechanical ad-vantage must be used to perform the work. Inrecovery, this means we must resort to the use oftackle. Tackle is classified as simple or compound.Simple tackle is one rope reeved on one or moreblocks to attain a mechanical advantage (fig. 10).Compound tackle uses more than 1 rope; it is acombination of 2 or more simple tackles, the out-put of 1 being used as the source of power for thenext (fig. 11). Since the equipment with whichrecovery is performed generally has only one line

2 TO I

3 TO I

Figure 10. Simple tackle.AGO 6473C 19


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from the source of power, simple tackle willnearly always be used. Compound tackle is de-scribed in TM 5-725; only simple tackle will bediscussed in this manual.

Section II. SOURCES OF POWER8. Winches

In recovery, because the force applied to move adisabled vehicle sometimes must be very great toovercome the resistance, mechanical means mustbe used. For this purpose, the most frequentlyused source of power is the winch. A mechanicalwinch is usually operated by a shaft driven fromthe power train of the vehicle on which it ismounted. The shaft operates through a worm geardrive to turn a shaft on which the winch drum ismounted. The principle of the inclined plane isused in the worm gear, and a mechanical advan-tage of from 20 to 1 to 50 to 1 may be gained inthe winch, depending on the type, make, model,etc. The drum is usually mounted on its shaft insuch a manner that it can be engaged when workis to be performed, or disengaged so the cable canbe paid out by manpower. A dog clutch of somesort is usually used to lock the drum to the shaft.A friction device is usually used against the endof the drum to prevent the drum from rolling toofreely and allowing the cable to overrun the drumwhen the rate of payout slows down. Winches usedin military vehicles have some means of brakingthemselves automatically when the power failsunder load.AGO 6473C 21


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a. A winch is most effective when the pull isexerted on the bare drum of the winch. As shownin figure 12, the leverage changes as each succes-sive layer of cable is wound onto the drum. Whena winch is rated at a capacity, that rating appliesonly as the first layer of cable is being wound ontothe drum. The winch capacity is reduced as eachlayer of cable is wound onto the drum due to theincreased diameter of the drum; the capacity ofthe winch may be reduced by as much as 50 per-cent when the last layer is being wound onto thedrum. (See table I for examples.) For thisreason, it is desirable to unreel all or most of thecable from the winch when it is used on heavyloads. Another advantage is gained by using thefull length of cable, because its natural elasticityor stretch prevents it from breaking so readily ininstances where sudden loads are applied.

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b. Ideally, the winch cable should be used insuch a manner that a line drawn through thelength of the cable will continue through thecenterline of the vehicle. If the cable is very faroff this line, it will lead to one side or the otherof the winch drum, pile up, and become damaged.The cable should not be used with more than 2deflection from straightaway. This deflection iscalled fleet angle (fig. 13) and becomes a very im-portant consideration in recovery when the winchis not equipped with a level winding device. Tomaintain the angle within the allowable limits, itsometimes becomes necessary to use an additionalblock, secured to a tree or other stationary objectand alined with the axis of the winching vehicle,and make the pull through an angle. This is illus-trated in figure 14. Some winches are equippedwith a device that travels back and forth acrossthe drum and guides the cable as it is reeled in .When a winch is equipped with such a device, fleetangle can be disregarded as long as the angle is nottoo sharp to permit the level wind unit to operate.9. Windlass

Where the resistance is not too great and awinch is not readily available, it is sometimes pos-sible to construct a windlass. A windlass consistsof a cylindrical device (like the log in fig. 15), onwhich a rope is wound, and which is turned by ahandle fastened at or near the end of the cylinder.The mechanical advantage gained by use of thewindlass can be determined by the radius of the24 AGO 6473C


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DRUMCENTERLINE

FLEETANGLE

, 2Figure 13. Fleet angle.

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Figure 14. Pull through an angle.

arc described by the handle in relation to theradius of the cylinder receiving the rope. Addi-tional advantage may be gained if the windlassis used in connection with tackle. When such acombination is used, the mechanical advantagegained by the tackle is multiplied by the mechani-cal advantage of the windlass to determine thetotal mechanical advantage. For example, in figure15, which illustrates such a combination, the me-chanical advantage gained by the tackle is 3 to 1;the handle of the windlass is 7 times as long as theradius of the log used as the cylinder, giving a26 AGO 6473C


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mechanical advantage of 7 to 1. By multiplying3 to 1 by 7 to 1, the total mechanical advantageis then 21 to 1. In the illustration, a tree has beencut into a log and one of the branches used as thehandle. The log is held in place by lashing it totwo trees. Other forms of this source of powercan be applied depending on the ingenuity of thepersonnel performing the job.10. Other Sources of Power

Power may be obtained, in many cases, by usingany available vehicle. A vehicle on sound, levelhardstand can usually move an object equal to itsown weight. If available, manpower may be usedto perform the work. One man can usually liftabout 100 pounds on a vertical pull, and pull about60 pounds on a horizontal pull. Sometimes, whena load must be lifted vertically, it is best to use ablock to change the direction of the rope so thepull can be made horizontally. Although one manpulls less, more men can be placed along a ropein the horizontal plane than a rope in a verticalplane (fig. 16).

Section III. RESISTANCE11. Forms of Resistance

Up to this point most of the discussion has beenon the effort, force, or power used to move anobject or overcome a resistance. Resistance hasnot been discussed to any extent except to indicatethat it was something that took force or power toovercome. In recovery, we are concerned withAGO 6473C 29


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several forms of resistance. The vehicle weight,combined with other factors, is used to determinethe resistance to be overcome in any recoveryproblem. There are means of making fast esti-mates that will be accurate enough for most cases.Resistance is created by the contact among me-chanical parts of the vehicle when effort is madeto move it. The type of terrain on which the vehi-cle is situated, whether it be mud, sand, or asmooth-surface road, will affect the resistancecreated. The grade or slope over which the vehiclemust be moved must also be considered. Some re-sistance is created by the tackle and must be addedto that created by the vehicle to determine thetotal resistance. When a vehicle is overturned aresistance must be overcome to bring it upright.These forms of resistance are explained in para-graphs 12 through 17 and the method of comput-ing them is given.12. Rolling ResistanceThe opposition to movement created by frictionwhen a vehicle is rolled over level ground is calledrolling resistance. Rolling resistance is affectedby the type of terrain. Exact figures are availablefor specific conditions of roadway but there are toomany variables to be of practical value; quickestimates are all that is necessary in recovery. Forexample, a vehicle on a smooth hard-surface roadwill create a resistance equal to about one twenty-fifth of the weight of the vehicle. The same vehiclein mud will create a resistance equal to or greaterthan its own weight. Table II gives the factorsthat may be used to estimate rolling resistance.30 AGO 6473C


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For mud, it will be noted that there is no factorgiven other than the minimum. Resistance willincrease with the increase in consistency anddepth of the mud. The rate of increase is given inparagraph 17.

Table 11. Terrain FactorsType of terrain Load on drawbarSmooth road _______________Vehicle weight

25Grass _____________________ Vehicle weight7Gravel ____________________-Vehicle weight

5Soft sand _____________-_____ Vehicle weight

4Mud ______________________- Minimum is vehicle weight.

Maximum pull dependsupon its depth and con-sistency.

13. Grade ResistanceGrade resistance is caused by gravity when a

vehicle is being moved up a slope, and it is deter-mined by that part of the vehicle weight which,because of gravity, is acting downhill. Table IIIgives the factor to be used to determine theamount of resistance. The angle of the slope maybe measured in either mils or degrees. Mil read-ings may be taken from the gunner's quadrant orthe degree of slope may be estimated. To use thetable, determine the amount of slop in degrees.(If the angle is measured in mils, divide thenumber of mils by 17.8 to obtain degrees.) Multi-AGO 6473C 31


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Table III. Factors Used to Determine Grade Resistance

s0 0S S 0

o N

1 .02 23 .39 45 .71 68 .932 .03 24 .41 46 .72 69 .933 .05 25 .42 47 .73 70 .944 .07 26 .44 48 .74 71 .955 .09 27 .45 49 .75 72 .956 .10 28 .47 50 .77 73 .967 .12 29 .49 51 .78 74 .968 .14 30 .50 52 .79 75 .979 .16 31 .52 53 .80 76 .9710 .17 32 .53 54 .81 77 .9711 .19 33 .54 55 .82 78 .98

12 .21 34 .56 56 .83 79 .9813 .23 35 .57 57 .84 80 .9814 .24 36 .59 58 .85 81 .9915 .26 37 .60 59 .86 82 .9916 .28 38 .62 60 .87 83 .9917 .29 39 .63 61 .87 84 .9918 .31 40 .64 62 .88 85 1.0019 .33 41 .66 63 .89 86 1.0020 .34 42 .67 64 .90 87 1.0021 .36 43 .68 65 .91 88 1.0022 .37 44 .70 66 .91 89 1.0067 .92 90 1.00

*If the angle has been measured in mils., divide the number ofmils by 17.8 to get degrees.

ply the weight of the vehicle by the factor oppositethe degree of slope to obtain the resistance createdby the grade. Add the results of this calculation to32 AGO 6478C


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the rolling resistance. Without use of the table, aquick estimate can be made of the grade resistanceby taking one-sixtieth of the weight of the vehicleand multiplying by the number of degrees of slope.14. Overturning Resistance

Overturning resistance is that part of theweight of the vehicle that acts against the forceexerted to bring it back on its wheels or tracks.Since half the weight of the vehicle is the maxi-mum weight that will ever be beyond the centerof gravity from the point of recovery, only half theweight of the vehicle will be resisting recovery.So at any time an overturned vehicle is to be up-righted, the resistance should be figured as halfthe weight of the vehicle.15. Tackle Resistance

The resistance of the tackle must be figuredwhenever tackle is used. The resistance from allother sources created by the vehicle becomes afactor in determining how much resistance iscreated by tackle. Due to the friction created bythe sheave rolling on the pin, the flexing on thecable, the cable scuffing in the groove of the sheave,and other factors, there is a loss in energy as thecable passes around each sheave. This loss isconsidered as resistance because it must be over-come before the load will be moved by the effortexerted. This resistance varies slightly amongdifferent size cables, but the variable is so smallthat for purposes of recovery it need not be con-sidered. Each sheave in the tackle can be expectedAGO 6473C 33


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to create a resistance equal to approximately 10percent of all resistances created by the vehicle andterrain. For example, if a vehicle to be recoveredcreates a resistance of 40,000 pounds, and 3sheaves are used in the tackle, a resistance of 30percent of 40,000 pounds would be created by thetackle, or 12,000 pounds.16. Total Resistance

When all the resistances created are added to-gether we have the total resistance to be overcome.The resistance will vary, of course, as conditionsvary. If recovery includes towing the vehicle, thesteepest grade will have to be considered. The typeof terrain over which the vehicle must be towed isalso important. As an example, if a 20,000-poundvehicle were to be towed up a 6 slope on pavedroad the total resistance would be 10 percent(from table III) of 20,000 pounds plus 1/2th of20,000 pounds or a total of 2,800 pounds of resist-ance. The same vehicle moved over a level sandroad would create nearly twice as much resist-ance: 1/4 th (table II) of 20,000 pounds or 5,000pounds. If the same vehicle became mired to thepoint where it could no longer proceed under itsown power, the resistance would increase to atleast the weight of the vehicle. Tackle resistancewould be considered if tackle were used.17. Field Method of Determining Resistance

It is seldom necessary to arrive at a preciseweight in recovery; a close estimate will generallysuffice. It is also difficult to use a mathematical34 AGO 6473C


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formula to determine the resistance of a vehicle inmud. A practical estimate may be made in thefollowing manner: when a vehicle becomes miredto the extent that it can no longer propel itself,the resistance to be overcome is at least equal tothe weight of the vehicle. (The weight of the vehi-cle can be obtained from the data plate in thevehicle or from the vehicle technical manual.)Vehicle weight can be used as an estimate until themud comes up to the top of the wheels. If thevehicle is mired to the fenders, the weight of thevehicle should be multiplied by two to estimate itsresistance. If the vehicle is mired to the turret orcab, the weight should be multiplied by three. Thetotal resistance of the object to be moved then,becomes the resistance created by the vehicle plusthe resistance created by the sheaves in the rig-ging. The method for determining tackle resist-ance remains the same as explained in paragraph15.

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CHAPTER 3RIGGING FOR RECOVERY

Section I. DISTRIBUTION OF EFFORT AND RESISTANCE18. Rigging

Rigging is the application of fiber rope, wirerope, or chain in various tackle and lever com-binations to raise or move a load. Rigging includesthe installation of all items necessary to employthe effort available and may or may not result in again in mechanical advantage. Rigging can beused to change the direction of pull and take ad-vantage of terrain features. Rigging may alsoinclude the assembly of tackle that creates me-chanical advantage. To be able to employ rigging,it is necessary to know its various parts and howeffort and resistance will be distributed amongthem. A law of physics (for each action there isan equal and opposite reaction) is applied fre-quently. When an effort is exerted on one end of arope there is an equal resistance applied at theother end. There is an equal amount of resistanceor effort, depending on how you look at it, appliedthrough the length of the rope even though therope may change direction as it passes throughblocks. A typical outlay used in rigging, and namesof its various parts, are illustrated in figure 17.36 AGO 6473C


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19. Fall LineThe line from the source of power to the firstblock is called the fall line. In recovery, the effort

available at the fall line is a factor that must beconsidered in every problem. Tackle must be usedwhenever the resistance to be moved exceeds theeffort available. If recovery is to be accomplished,mechanical advantage must be increased until thetotal resistance divided by the mechanical advan-tage results in a figure less than the effort avail-able at the fall line.20. Return Lines

The lines between the blocks, and the line fromthe last block in the rigging to the point where theend of the line is fastened, are return lines. Dueto the equal and opposite reaction referred to inparagraph 18, each return line will exert a forcein each direction equal to the effort placed on thefall line. Since this is true, each line going to oraway from the load to be moved will exert a forceon the load equal to that on the fall line. Sinceeach line going to or away from the load exerts anequal force, the mechanical advantage derivedfrom the tackle is equal to the number of linessupporting the load. In figure 17 the fall line and2 return lines support the load to provide a me-chanical advantage of 3 to 1.21. Dead Lines

The equipment that is used to fasten items inthe rigging but that does not become active during38 AGO 6473C


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the performance of work makes up the dead line.Dead lines are used to fasten blocks to the load, tofasten blocks to an anchor of some sort, or tofasten the end of the line from the source of powerto the load or anchor. In most instances, the deadline must withstand more than any other line inthe rigging because when it is used to fasten ablock, it must withstand the force coming to andgoing away from the block. The strength' f thedead line should be checked very closely beforerecovery is attempted.

Section II. ROPE AND CHAIN22. Fiber Rope

There are several kinds of fiber rope availableand each has a different strength. The strength ofrope of the same type will vary after it has beenused, after it has been wet, or after it has collecteddirt between the strands. Fiber rope has verylittle use in recovery except for relatively lightloads. The strength of new rope can be estimatedby using the formula T=4D2. The T equals thecapacity in tons; D equals the diameter of therope. Therefore, with a 1/2-inch rope, T=4 X (1/2 X1/2)=4X1/4=1 ton. If the rope is to be used tohandle expensive loads or if personnel would beendangered if the rope broke, the results should bedivided by 4 to provide safe working strength.Fiber rope should be inspected closely, before it isused, for any indication of weakness that mightcause it to break easily. Rope should not be pulledover sharp edges or abrasive material.AGO 6473C 39


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23. Wire RopeConstruction of wire rope is explained in TM 5-725. Wire rope is used on winches and for tow

cables. The strength of wire rope that the Armyuses can be estimated by application of the for-mula T-40D2 . As in fiber rope, T equals thestrength in tons; D equals the diameter of therope. In most instances, where the size of the ropeis stated in fractions of an inch, it is easiest toconvert the fraction to a decimal before makingthe computations. As an example, the strength ofa 3 /4 -inch wire rope would be 3/ X 3/4 or .75X.75=.5625 X 40=22.5. The strength of the rope is221/, tons. Safety precautions to be observed whenwire rope is used are outlined in paragraphs 38through 40. The breaking strength of certain sizesof wire rope as computed by the formula is shownin table IV. The strength will be slightly less thanthat shown for a new wire rope.

Table IV. Breaking Strength of Fiber andWire Rope in TonsRope capacities in tons

Diam ininches Fiber (sisal) Wire (IPS)% 1 10%/8 1.56 15.622.25 22.57/8 3.06 30.621 4 401% 5.06 50.62

11/4 6.25 62.5Note. For safe working strength, divide the breaking strength of

fiber rope by 4: of wire rope by 5.

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24. ChainThe strength of chain is calculated by the same

formula as for wire rope. To determine the diam-eter of chain, one side of the link is measured.Chain should be inspected frequently for cracksin the links, especially at the weld if welded linksare used. Chain should not be painted because acrack may not be detected through the paint andresult in a hazard to personnel and equipment.

Section III. ANCHORS25. General

a. Frequently, it is necessary to have somemeans of anchoring when heavy loads are handledby means of tackle.b. Natural and temporary or permanent man-made anchors may be used for rigging. Whereverpossible, for speed and economy, natural anchorsshould be used. Temporary anchors includepickets, holdfasts, and deadmen. Permanentanchors may be made up of steel anchors set inconcrete or fastened to permanent structures.Lines should always be fastened to anchors at apoint as close to the ground as possible. The linefrom the anchor should be as nearly parallel to theground as possible to avoid pulling the anchor outof the ground. It is better to link two or moreanchors together than to use a single anchor, be-cause multiple anchors spread the load over agreater area of the ground. Greater strength toocan be attained by linking anchors together, secur-AGO 6473C 41


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ing a point high on one anchor to a point near theground on the anchor behind it.26. Natural Anchors

a. Trees, stumps, or rocks can be made to serveas natural anchors for rapid recovery in the field.Always attach lines near the ground on trees orstumps. Avoid dead or rotten trees or stumpsbecause as anchors they are likely to snap when astrain is placed on the line. It is always advisableto lash the first tree or stump to a second one, toprovide added support for the line.

b. When using rocks as natural anchors, ex-amine the rocks carefully to be sure that they arelarge and embedded firmly in the ground. An out-cropping of rock or a heavy boulder buried par-tially in the ground will serve as a satisfactoryanchor.27. Constructed Anchors

There are several ways of constructing anchorswhen natural anchors are not available.a. A picket holdfast may be constructed by driv-ing a single steel or wooden picket into the groundas a stake. You may make a stronger holdfast oftwo or more sound pickets at least 3 inches indiameter and 5 feet long (fig. 18). Drive thepickets 3 feet into the ground, 3 to 6 feet apart,and in line with the dead line. If fiber rope is used,tie it to the front picket with a clove hitch andmake from 4 to 6 turns around both pickets, fromthe bottom of the rear to the top of the front42 AGO 6473C


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picket. Then, fasten the rope to the rear picketwith a clove hitch just above the turns, pass astake between the rope turns, and tighten the ropeby twisting it and driving the stake into theground. Repeat this operation for each successivepair of pickets. The strength of the holdfast de-pends mainly upon the strength of the first orfront picket. To reinforce the front picket, drivetwo or more pickets into the ground close together,and lash them before lashing the front and rearpickets (fig. 19). In wet earth, the holding powerof holdfasts is greatly reduced. The approximatestrengths of picket holdfasts are shown in table V.Table V. Holding Power of Picket Holdfast in Loamy Soil

Holdfast Pounds

Single picket --_______________________________ 7001-1 picket holdfast combination ________________- 1,4001-1-1 picket holdfast combination - -______________,8002-1 picket holdfast combination -________________ 2,0003-2-1 picket holdfast combination ______________- 4,000

Note. Wet earth factors:Clay and gravel mixtures ................ 0.9River clay and sand...................... 0.5

b. For heavier loads in soft or wet earth, youmay use the combination log-picket holdfast. Withthis holdfast you must fasten the anchor or deadline to a timber supported against several (4-6)picket holdfasts (fig. 20). The strength of thistype of holdfast depends upon the strength of thetimber as well as of the pickets. You must, there-AGO 6473C 43


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Figure 18. 1-1-1 combination picket holdfast.

Figure 19. 3-2-1 combination picket holdfast.

fore, select a timber big and strong enough tostand the maximum pull on the dead line withoutbending appreciably.

c. A deadman is one of the best types of anchor.It is used for heavy loads or more permanent in-stallations. The deadman consists of a log, timber,steel beam, or similar object buried in the groundwith the dead line connected to it at the center.44 AGO 6473C


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Figure 20. Combination log-picket holdfast.

When constructing a deadman, place it where thedirection of pull is as nearly horizontal as possible.Take advantage of sharp banks or crests to de-crease the inclination of dead lines and to increasethe holding power with less digging. Dig the holelarge enough for the deadman and as deep as nec-essary for good bearing. You should also slant thebank in the direction of the pull at an angle ofabout 15 from the vertical and undercut towardthe load. To strengthen the anchor, drive stakes infront of the deadman at each end. Dig a narrowtrench on an incline for the dead line, bearing tothe center of the deadman. Tie the dead line to thecenter of the deadman so the main or standing partof the line leads from the bottom of the deadman.This helps to prevent the deadman from rotatingout of the hole. If the dead line has a tendency tocut into the ground, place a log or small boardunder the line at the outlet to the inclined trench.AGO 6473C 45


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Figure 21. Log deadman.

A log deadman is illustrated in figure 21. Thestrength of the deadman depends partly on thestrength of the log or object buried, but mainlyon the holding power of the earth.

d. In sandy areas with no trees, a sand para-chute may be used as an anchor. A sand parachuteis constructed by digging a large, deep hole, andlining it with a tarpaulin. The tarpaulin is thenfilled with the sand removed from the hole, thefour corners are lashed together, and the riggingis attached. The sand parachute is illustrated infigure 22.

e. A variation of the sand parachute, the sandparachute deadman, may be constructed in asimilar manner as the sand parachute. After thehole is dug, the spare tire and wheel assembly isplaced in the hole. The dead line is secured to thewheel, the tarpaulin emplaced, and the hole re-filled. Unlike the sand parachute, the corners of46 AGO 6473C


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Figure 22. Sand parachute.

the tarpaulin are not drawn together. Figure 23illustrates a sand parachute deadman.

f. Each wrecker truck is equipped with twoground anchor sets as items of issue. One set con-sists of 3 anchors, 10 stakes, and one 10-poundsledge hammer. The anchor is installed as illus-

Figure 23. Sand parachute deadman.AGO 6473C 47


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000

0

wmIC u -i 0o z~~~~~~~~~~~~~~~~~~~w9U 0~~~~~~~~~~~~~4 z 4 U~~~~~~0 F

o 0t0tx

48O AG 43

th

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trated in figure 24. The stakes are driven into theground until only 6 to 8 inches remain above theanchor. If more than one anchor is used, they maybe set in series, as illustrated. In clay soil, eachstake is capable of holding slightly more than 1ton. One anchor with 5 stakes will hold approxi-mately 6 tons; 2 anchors with 10 stakes, about 12tons. To remove the stakes after the anchor hasbeen used, the stakes should be struck a solid blowat the base; this will usually loosen them enoughto remove them. If the ground is too hard, thewrecker boom can be used to pull up the stakes.No more than 2 sets of these anchors should beplaced in series (10 stakes) without reinforcingthe stake to which the dead line is attached. Aforce greater than 12 tons will cause the stake tobend.

g. Another vehicle can be used as an anchor ifit is available. The resistance offered by the vehi-cle, with its brakes set, very often is adequate toresist the pull of another vehicle during recovery.The vehicle can be used in conjunction with otheranchors, to give it additional resistance, by using achain or rope between it and the other anchor.

Section IV. RECOVERY PROCEDURES28. Reconnoitering the AreaCheck the terrain for an approach to the load,method of rigging, and natural anchors. As witha tactical mission, a recovery crew must know theproblem before decisions are made. A completeAGO 6473C 49


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reconnaissance should be made of the area if thetactical situation permits. The reconnaissanceshould include selection of the best route of ap-proach, which is usually the reverse of the routetaken when the vehicle became disabled. Whenpositioning a recovery vehicle, the crew shouldalways take care to prevent its becoming disabledand to insure proper fleet angle of the winch cable.The recovery vehicle should be positioned so thefall line will remain at or near a right angle to thewinch drum. If this is impossible or difficult toachieve, an anchor should be used to fasten ablock in such a manner that the cable will pullthrough an angle. The method of erecting riggingshould be determined according to the distancebetween the disabled vehicle and recovery vehicle,as explained in paragraph 36. Considerationshould be given to the location and use of availablenatural anchors to support part of the rigging orto anchor the recovery vehicle.29. Estimating the Situation

Determine the resistance of the load and thecapacity of the effort available. An estimate of theminimum resistance to movement of the disabledvehicle will be the weight of the vehicle plus itscargo. The resistance will vary, depending uponthe type of disablement, as explained in para-graphs 14 and 17. The amount of effort availableshould also be determined. For a recovery vehicle,this would be the capacity of the winch. The winchcapacity is usually stated on the winch data plate,50 AGO 64.7:.C


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and is always stated in the vehicle technicalmanual.

30. Calculating the RatioThe need for a mechanical advantage becomesnecessary whenever the resistance of the load ex-ceeds the capacity of the effort available. Theamount of mechanical advantage for the riggingmay be estimated by dividing the resistance of theload by the effort available. The reason the me-chanical advantage is estimated at this stage isbecause the tackle resistance is unknown. It ispossible that because of limited equipment duringsome recovery operations, sufficient mechanicaladvantage cannot be rigged. In this case, anotherrecovery vehicle should be brought in to providethe additional effort required.31. Obtaining Total Resistance

Before the load can be moved, the amount ofresistance to movement created by both the tackleand the load must be overcome. Total resistanceis determined as explained in paragraphs 16 and17. Tackle resistance can develop into a majorfactor of the total resistance.32. Verifying th e Solution

Compute line forces and compare them with thewinch and dead line capacities. This step is thekey to quick, safe, and successful vehicle recovery.The mechanical advantage estimated in paragraph30 is checked for accuracy by computing the effortrequired on the fall line and then comparing it toAGO 6473C 51


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the capacity of the winch. The effort needed isdetermined by dividing the total resistance by themechanical advantage. To move the load, the effortrequired on the fall line must be less than thecapacity of the winch. If the effort required, isgreater than the capacity of the winch, the me-chanical advantage of the rigging must be in-creased. The force imposed on all dead lines is alsocomputed and compared to their capacity to insurethat they are not overloaded. Dead line force isdetermined by multiplying the amount of fall lineforce by the number of lines the dead line sup-ports. The capacity of wire rope and chain thatmay be used as dead lines is explained in para-graphs 23 and 24. Verifying the solution will notonly save time by preventing rerigging, but willalso contribute to safety by reducing the elementof chance to a minimum.33. Erecting the Rigging

Orient the crew and instruct them to assemblethe rigging and then move to a safe location. Therecovery chief should advise other crewmembersof the plan and assign them duties to erect therigging. To save time, work should be distributedso each individual has a task that will be finishedin approximately the same time as the next man's.Crews should be instructed that those who finishfirst should assist those who have difficulty. Aftererecting the rigging, the crew will be moved to asafe location (par. 39).52 AGO 6473C


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34. Rechecking the RiggingInsure that the rigging is erected for proper and

safe operation. The recovery chief will direct theoperator to remove most of the slack from therigging; he then will inspect the rigging to insurethat all fastenings are installed properly andsafety keyed, that the cable has no loops, and thatthe hook points are facing upward. Make anycorrections necessary in the rigging at this time.The recovery chief then moves to a safe locationwhere he can observe the entire recovery opera-tion. He directs the operator to close his hatch andobserve through the periscope for signals.35. You Are Ready for Recovery

Signal the operator to apply power to the winchand recover the load. Power should be appliedslowly to prevent an impact (par. 40c). The re-covery chief must be alert during the recoveryoperation, insuring that nothing obstructs therigging, and that no one is endangered. After thevehicle is free, he signals the operator to placeslack in the rigging, and instructs the crew to dis-assemble the rigging and stow the equipment.

Note. To accomplish vehicle recovery successfully, allpersonnel concerned must follow some workable plan. Ahaphazard approach to a recovery problem usually resultsin unsafe practices and, more often than not, in failure.Paragraphs 28 through 35 outline an eight-step procedure,in the proper sequence, that should be followed during allrecovery operations requiring winching. To assist inmemorizing these steps and their sequence, they are soarranged that when placed in the proper sequence, the firstletter of each step will spell out the word recovery (fig.AGO 6473C 53


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RECOVERY PROCEDURE

RECONNOITER AREA

ESTIMATE SITUATIONCALCULATE RATIO

OBTAIN RESISTANCE

VERIFY SOLUTIONERECT RIGGING

RECHECK RIGGING

YOU ARE READYFigure 25. Recovery procedure.

25). This plan is not restricted to recovery crews forapplication and supervision, but is also of value to com-manders for determining the efficiency of their recoverycrews and the need for training.

Section V. RECOVERY TECHNIQUES36. Assembling the Rigging

a. The backup method is used when the re-covery problem is such that the recovery vehicle54 AGO 6473C


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can approach very close to the vehicle to be re-covered, thus requiring little effort on the part ofthe crew to erect the rigging. The winch rope canbe handled by crewmen, reeved through thesheaves, and anchored as necessary because onlya small amount of the rope must be removed fromthe winch and handled. The dotted outline infigure 26 shows the vehicles in position to hook up.However, the hookup is only the first step whenrecovery is being made because, as explained inparagraph 8a, to be most effective, the pull fromthe winch must be made as the first layer of rope isbeing wound onto the drum. After the hookup iscomplete, the winch must be in neutral, the brakereleased, and the recovery vehicle backed up untilmost of the rope is off the winch drum. The solidoutline in figure 26 shows the vehicles in positionto start recovery. The capability of the winch willbe increased as each layer of rope leaves the drum.It may also be said that as each layer of rope iswound onto the drum, the capacity decreases.Sometimes, when a pull is being made and therecovered vehicle must be pulled a relatively longdistance through mire, it may be necessary to usethe backup method to regain winch capacity andcomplete the job.

b. The lead method is used when the miredvehicle has gone so far into the mire before be-coming immobilized that it would not be advisableto get close enough with the recovery vehicle to usethe backup method (a above). The lead methodconsists of using the auxiliary winch to haul theAGO 6473C 55


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t 11w

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main winch cable to the mired vehicle. The auxil-iary winch cable weighs less and can be handledby crewmembers, while they would probably beunable to carry the main one. To rig for the leadmethod, the auxiliary winch cable should be payedout to give a two-part line from the recovery vehi-cle to the mired vehicle. The main winch cable canthen be payed out far enough to reeve the snatchblock into a loop; the end of the cable should beanchored at the recovery vehicle. It is now possibleto attach the auxiliary winch cable to the block onthe main winch cable and, with the winch in neu-tral and the brakes released on the main winch,to use the auxiliary winch to pull the larger cableout to the disabled vehicle. This will provide a 2 to1 advantage from the main winch cable when it islead to the disabled vehicle (fig. 27). Figure 28shows the relative positions of the vehicles and therigging necessary to lead a 3 to 1 mechanical ad-vantage to a disabled vehicle.

c. No problem exists in handling cables for thewheeled wrecker. The cable is lighter and may becarried by crewmembers to where it is needed.37. Attachments to Vehicle To Be Recovered

In recovery operations, it is important that rig-ging be attached to the vehicle in such a manner asto avoid damage. For example, in recovery of adisabled wheeled vehicle, the winch cable shouldnot be attached to the bumper because the bumpermight be damaged. The frame could be pulled outof alinement if the cable were attached where theeffort was applied to a single frame member.AGO 6473C 57


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a. On wheeled vehicles, whether the pull ismade from the front or rear, the effort should beapplied to the lifting shackles (fig. 29). To applythe effort equally to both shackles, a sling shouldbe used between the tw o shackles and the effortapplied to the sling. A chain is the best item to useas a sling. If mechanical advantage is used, theblock will be attached to the sling and the winchcable reeved through the block (fig. 30). When asling is used in this manner the effort exerted oneach side of the sling will be slightly greater thanhalf the effort exerted by the winch. As the angleof the sling increases (the sling becomes shorter)the load on the sling becomes greater. To keep theload within safe limits, the angle of the slingshould be kept at less than 30; the apex of the

Figutre 29. Wheeled vehicle rigged for a direct pull.AGO 6473C 59


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angle formed by the sling should be at least 6 feetfrom the vehicle (fig. 31). The formula for meas-uring the load on a sling can be found in TM5-725.

b. When attaching the rigging to a trackedvehicle, always use the towing hooks or towingeyes. The lifting eyes and towing pintle of atracked vehicle are not designed to withstand theload necessary for recovery. To prevent pullingthe vehicle sideways and increasing the load, it isbest to use a hookup that will distribute the effortequally to each side of the vehicle. To save time,consideration should also be given to whether thevehicle will be able to proceed under its own poweror will have to be towed after it is recovered. Time

Figure 30. Wheeled vehicle rigged for a 2 to 1mechanical advantage.

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6 FT.

SLINGFigure 81. Sling arrangement.

and effort will be saved if the one hookup can beused for both winching and towing.(1) If the disabled vehicle will not requiretowing and the mechanical advantage

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does not exceed 2 to 1, the best methodfor recovery is by use of the floatingblock (fig. 32). This hookup is easy toinstall and will give an equal distributionof the effort to both towing hooks. Torig a floating block, hook the ends of thetow cable to the two tow hooks; place asnatch block in the sling formed by thetow cable, and use heavy-duty shackles toattach the winch rigging to the block.

(2) If the disabled vehicle will have to betowed over extremely rough terrain afterrecovery, it is best to use two tow cables(fig. 33). Attach a tow cable to each towhook. Form a sling by fastening the twofree ends to the block with shackles. At-

62 Figure 32. Floating block. AGO 6473C


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Figure 33. Tow cables.

tach the winch cable to the shackles.After the recovery, disconnect the winchcable, cross the two tow cables, and at-tach them to the tow hooks on the re-covery vehicle.

(3) If the vehicle is to be recovered and towedover relatively level terrain or on a high-way, the best hookup can be made with atow bar (fig. 34). The tow bar can beattached to the towing eyes of the dis-abled vehicle; the block on the winchcable can be fastened to the tow bar byshackles. After the recovery operation iscomplete, the tow bar can be attached tothe towing pintle of the recovery vehicleand the disabled vehicle towed to itsdestination.

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Figure 34. Tow bar.

Figure 35. Tracked vehicle rigged for a 3 to 1mechanical advantage.

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(4) If a 3 to 1 mechanical advantage is to beused, the end of the winch cable can befastened to one of the tow hooks on thedisabled vehicle. The snatch blockthrough which the winch cable is passedcan be fastened to the towing eye on theother side of the vehicle by using a heavyduty shackle (fig. 35).

Section VI. SAFETY38. Handling Cables

When cables must be handled by hand, heavy,leather-palmed gloves should be used to protect thehands from being cut by any broken wires in therope. A broken wire will cause a severe cut, whichis generally slow to heal. Care should be used toprevent the wires from breaking during use.Cables or ropes should not be drawn over sharprocks, around sharp corners, or through sheavesthat are designed for larger or smaller cables orropes, and they should not be struck with an objectthat would cause a nick or burr to form andweaken the strand.39. Observing

To avoid accidents from taut cables or ropes,the following precautions should be observed:

a. Stand clear of any cable under tension. Whena cable is drawn taut and then suddenly releasedby a break, its recoil or backlash can cut a man inhalf. A winch line under tension stretches like aAGO 6473C 65


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rubber band and stores up a lot of energy. If sucha line should break, its snapping back could becompared to a rifle bullet except that when thebullet strikes, it makes a fairly clean hole; thewinch cable makes a messy wound. The idea is totreat a cable under stress with the same respectyou would a loaded gun.

b. Before a pull is begun, all persons must beevacuated from within the angle formed by thecable. A winch line is similar to a slingshot in thatif a deadline to a snatch block breaks, a 200-poundblock can be thrown as far as 300 yards. Allpersons observing the operation should stand out-side the angle formed by a cable under load andat a distance equal to at least the distance betweenthe two most distant points in the rigging. Unsafeareas are illustrated in figure 36.40. Miscellaneous Safety Precautions

There are several other areas where the safetyof personnel and equipment must be observed.

a. Operators and other persons in either the re-covery or disabled vehicles should keep the hatchesclosed during a recovery operation if the amountof rope (cable) between the two vehicles is equalto or greater than the distance between thepersons and the closest point of the rope. If a 10-foot tow rope is being used between two vehicles,all hatches within a 10-foot radius of the rope(from both ends of the rope) should be closed ifthe compartment is occupied.66 AGO 6473C


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- UNSAFE AREA

Figure 36. Unsafe areas.

b. All loops in cables should be straightenedwhile the rope is slack and before the load is ap-plied. When a load is applied to a looped wirerope, a kink will result; the strands separate orAGO 6473C 67


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break, and the rope is damaged and weakened.To remove a loop, the rope should be bent backopposite from the direction in which the loop wasformed. The loop cannot be straightened by pull-ing the rope taut; this merely separates or breaksthe wire in the strands of the rope (fig. 37).

c. Loads should not be applied suddenly. Suddenloads are caused by operators who permit an ob-ject to drop or roll until the slack is taken up inthe rigging, causing the load to stop suddenly, orwho accelerate the recovery vehicle and take upthe slack in the rigging suddenly. In either casethe same effect occurs-an excessive strain is

Fiygire 37. Kink in wire rope pulled taut showsseparated wires in the strand.

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placed on the rope. This sudden force, like theblow of a hammer, is hard to compute accurately,but it is very great.

d. Except for certain cases such as towing,cables and ropes should be rigged so that no lineswill cross and rub one another. Two cables underload will cause a great pressure to be exerted, aswell as the loss of power by friction. The wire orfiber in the strands may be broken where theycross and rub. Such a condition can usually beavoided by proper placement of the ropes in theblock. If such a condition occurs, ropes should bererigged and the rubbing eliminated before effortis applied.

e. Blocks or chains in the rigging should beplaced so that when strain is placed on the rigging,the point of the hook will be pointing upward.The hook will probably be one of the most vul-nerable points in the rigging; it will have a tend-ency to straighten out under load. By placing thepoint of the hook upward, the tendency will be forthe rigging to travel downward when or if thehook straightens. Therefore, less damage is likelyto result than if the rigging traveled upwardunrestrained.

f. To prevent damage to equipment, it is betterto employ a greater mechanical advantage thanrequired than to use a hookup that loads the equip-ment to capacity. Equipment will last longer,cables that have been weakened will not break asreadily, and operations will be more successful,generally. Recovery crews will take more pride inAGO 6473C 69


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their work if their operations are consistentlysuccessful. Less work will be necessary if the timerequired for rerigging is held to a minimum.

g. When rigging is being connected or discon-nected during a recovery operation, the engine inboth vehicles should be shut off. The possibility ofa vehicle being placed in gear accidentally and in-juring somebody is eliminated if the engine is notrunning. It is also necessary to insure that park-ing brakes are in good condition, and applied.h. Safety keys should be in place on all towhooks and shackles.

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CHAPTER 4FIELD EXPEDIENTS

41. GeneralAny vehicle may become disabled from time totime. Because tactical vehicles do not always oper-

ate on or near roads where help would be easy tofind, at times you and your disabled vehicle may bealone. If so, it may be your job to get the vehicleto operate again without the aid of recovery vehi-cles. You may have only the equipment on thevehicle, the natural surroundings, and your owncommonsense and good judgment. If you are inthis predicament, a little thought before you startanything may save several hours of unnecessarylabor or keep you from having to wait until a re-covery crew can find you. You should consider useof the methods below to return a vehicle to opera-tion under these conditions. These methods arecalled field expedients. You should be familiarwith field expedients and be prepared to use them.Always remember to observe the safety precau-tions outlined in paragraphs 38 through 40.42. Steering Action

A number of field expedients for tracked vehi-cles are based on the way the steering controlsAGO 6473C 71


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work. If your vehicle has thrown or broken atrack, you can move the vehicle by applying steer-ing action in a forward or reverse range. Thistransmits power to the side with the good track,and moves your vehicle either forward or back-ward. However, if you do not apply steering ac-tion, the vehicle will not move, because the poweris transmitted only to the sprocket without thetrack, which will be free to turn.43. One Track Spinning

To move a tracked vehicle that has one track onsolid ground and the other spinning in the mud,apply steering action to the spinning track. Thiswill stop the differential action and cause powerto be transmitted to both tracks. If one track is onsolid ground, it will move the vehicle. As soon asthe effect of steering is felt and the vehicle beginsto turn, return the steering to straight ahead.44. Slippery Hill

To move a tracked vehicle up a slippery hill orincline, attach one end of a cable to a track, andthe other end to an anchor (fig. 38). If the othertrack slips, apply steering action and move thevehicle until the end of the cable passes the endroadwheel. Stop the vehicle, disconnect the cableand, if the vehicle still cannot gain traction, repeatthe procedure.45. Bellied Tracked Vehicle

Very often vehicles become bellied (highcentered) on stumps, rocks, dry ridges, or mire.72 AGO 6473C


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Figure 38. Anchoring one track with cable.

In this position, tracked vehicles are helpless be-cause both tracks are held clear of the ground andcannot get enough traction to move the vehicle(fig. 39). To recover a vehicle bellied on anobstacle, attach a log to both tracks at one end ofthe vehicle. If there is no log available, connectthe two tow cables of the tank together and, usingthe towing hooks from the vehicle, attach to bothtracks. Then apply power gradually to the tracks;the log or tow cables will strike the obstacle andmove the vehicle. Care must be taken to stop thevehicle when the log or cable reaches the rear orfront of the tracks, or it will damage the fendersand tow cable. A log is preferable for use in mud.AGO 6473C 73


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CABLE SECUREDAROUNDLOG AND TRACK

Figure39. Log used to anchor tracks.

Figwre 40. Cable used to anchor tracks.74 AGO 6473C


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46. Broken or Damaged Suspension SystemTo operate a vehicle with a damaged roadwheel,

spindle, or roadwheel arm, the arm should be tiedup out of the way (fig. 41). To tie the roadwheelup, the torsion bar should be removed. This can bedone by placing the tank across a ditch narrowenough to permit the front and rear roadwheels tobe supporting most of the weight of the vehicle,and deep enough to permit the track to sag awayfrom the affected roadwheel. If a ditch is not avail-able, a trench can be dug. With the tank in thisposition, the tension on the torsion bar has beenreleased and the bar can be removed. The road-wheel can be tied up and out of the way. Thisexpedient cannot be used on the front or rearroadwheels.47. Thrown Tracks

To move a tracked vehicle when both trackshave been thrown, use one sprocket as a winch. Todo this attach a cable to the sprocket so it willwind up when the sprocket turns. Attach theother end of the cable to an anchor, then applysteering action to move the vehicle (fig. 42).48. Breaking a Thrown Track

To break a thrown track under emergency orcombat conditions, or when time is a major factor,it has been found practical to remove the centerguide and, using the oxyacetylene welding equip-ment found on wreckers or recovery vehicles, cutthe track connector on each side of the track.AGO 6473C 75


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A. THIRD AND FOURTH ROADWHEELARMS TIED UP.

B. INGLE ROADWHEEL ARM TIED

B. SINGLE ROADWHEEL ARM TIEDUP TO CROWBAR.

Figure 41. Damaged roadwheels tied up away fromtrack (roadwheels removed).

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CDC

fr< I

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49. Remounting a TrackTo remount a track, lay the track out in front

or rear of the vehicle in line with the roadwheels.Then shift into forward or reverse range (which-ever is desired) and apply steering action; thevehicle will then pull onto the broken track. Toremount both tracks, lay them out in front or rearof the vehicle in line with the roadwheels. Attachone end of a cable to one of the sprockets so thatit will wind around the sprocket hub, and attachthe other end to a suitable anchor. Place the shiftlever in gear, and apply steering action. The powertransmitted to the sprockets will cause the cableto wind around the sprocket hub and pull the road-wheels up onto the broken tracks.50. Linking a Broken Track

Very often a track must be linked together with-out the aid of a track jack. To do this, link adouble-pin-type track together by winding a lightcable around the track pins as shown in figure 43,attaching the cable ends to another vehicle, andpulling the two track ends together. When thepins become close enough to each other, install thetrack connectors part way, remove the cable, ham-mer the connectors into position, and install thewedges and center guide.51. Slave Cable Starting

Slave cables are available in both second-echelonspecial toolsets and the equipment of wreckertrucks and recovery vehicles. Slave cable starting78 AGO 6473C


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LIGHT CALECLE

Figure 43. Linking a broken track.is intended for engines on vehicles that have dis-charged or partially discharged batteries. It isdone by using another vehicle with fully chargedbatteries as the source of power. The startingprocedure is outlined in TB ORD 537 and in yourvehicle technical manual. Become familiar withthe procedure. Much damage can be done by usingincorrect slaving procedures.52. Use of an A-Frame (Shears)

Frequently a truck will become nosed in a shell-hole or narrow ditch. When a truck becomes dis-abled in this manner, both lifting and pullingforces are required to make the recovery. The lift-ing force can be obtained from an A-frame when


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a wrecker truck is not available. To construct anA-frame, 2 poles approximately 8 feet long andlarge enough in diameter to support the front endof the truck will be needed. The poles should belashed together at the top by a figure-8 or girthhitch. The lower ends should be placed in theground 10 to 12 inches deep to prevent them fromsliding when power is applied. The upper end ofthe A-frame should be laid across the hood of thevehicle and the attachment made as in figure 44.If the nosed truck is equipped with a winch, thewinch cable should be rigged for a 2 to 1 mechani-cal advantage, with the end of the cable secured tothe apex of the A-frame. If a separate truck isneeded because the nosed truck is not equippedwith a winch, a block should be attached to theapex of the A-frame and a 2 to 1 mechanical ad-vantage rigged from the truck emplaced in frontof and alined with the nosed vehicle.53. Use of Logs to Cross DitchesIn field operations, ditches will often be en-countered that are too deep to drive through. Aconvoy of mixed wheeled vehicles may cross sucha ditch by using five logs. The logs should beapproximately 10 inches in diameter, from 3 to 4feet longer than the span, and positioned as illus-trated in figure 45. This arrangement will passa wheeled vehicle convoy without rearrangementof the logs. To prevent the logs from spreadingapart, stakes should be driven into the ground onboth sides of the logs and the logs should belashed together at the center with a chain, wire,80 AGO 6473C


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Vi :?

:9

Figure 44. Recovering a nosed truck with an A-frame.

AGO 6473C 81


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GIRTH HITCHON

A-FRAME

FIRST STEP

SECOND STEP THIRD STEP

LOOPUSTTOW HOOK TO

SLFOURTHTEPIFTH STEPFOURTH STEP FIFTH STEP

Figure 44-Continued.

or rope. Only two logs would be required to passa dual-wheeled vehicle across the ditch. The frontwheels can be converted to duals by using thespare wheels or by removing the outer wheels ofone of the sets of rear duals, and allowing thedual wheels to straddle the logs as the vehiclecrosses. Four logs would be necessary to pass avehicle equipped with single wheels. By lashingthe logs together in pairs, the wheels would ride be-tween the logs. To permit a narrow-tread vehicleto cross, the logs may be moved closer together or


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a fifth log may be added. Vehicles must be drivenslowly, in low gear, and a guide must be providedto insure that the vehicle and the logs are alinedproperly.54. Use of Wheels for a Winch

When a wheeled vehicle is not equipped with awinch, the rear wheels may be used to assist inrecovering the vehicle. On a dual-wheeled truck,a rope with one end fastened to the wheel huband the other end anchored can be wound up onthe wheel or hub to give the same results as awinch. The end of the rope that is fastened tothe wheels should be run between the duals andthrough one of the holes in the wheel disk. Abowline knot can then be tied in the end of therope and slipped over the end of the hub (fig.46). By placing the vehicle in reverse gear, therope will wind between the two duals and thevehicle will move to the rear (fig. 47). Careshould be taken to place the rope through a holein the wheel where the valve stem will not bedamaged. If the truck has single wheels, thesame system can be used by placing a bar throughthe hole in the end of the axle flange. The ropecan be started by fastening it to the bar with afigure-8 hitch, and the rope will wind in behindthe bar, as illustrated in figure 48.55. Recovery Vehicle Used as a Tramway

Wheeled vehicles may be transported across ariver or ravine by a tramway erected by using arecovery vehicle and its winches. The recovery84 AGO 6473C


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Figutre 46. Attachment of rope to dual wheelsto be used as a winch.

vehicle should be on solid footing, as close to theedge of the bank as possible, and with workingspace in front of the vehicle. One crewmemberwill be required to reach the opposite bank witheither a light rope or, if available, a length oftelephone field wire long enough to span the riveror ravine to be crossed. In the case of a river,it is probable that the crewman will have to swimto the opposite shore with the rope. The rope orAGO 6473C 85


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Figure 47. Using wheels as a winch.

field wire, now stretched across the ravine orriver, can be used to pull a snatch block, ananchor chain, and the auxiliary winch cable fromthe recovery vehicle to the opposite side. On theopposite side the block should be anchored to atree or other suitable anchor, and the winch cablereeved through the sheave and passed back acrossthe river. (It is sometimes possible to do this byattaching a weight to one end of the rope or tele-phone wire, swinging it around to create momen-tum, and throwing it across the river.) Whenthe crewmember at the vehicle receives the rope,86 AGO 6473C


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S *... : .

Figure 48. Attachment of rope to single wheelto be used as a winch.

he can pull the end of the auxiliary winch cableback to the recovery vehicle. The main winchcable and the boom winch cable can now be at-tached to the auxiliary cable and drawn acrossthe ravine or river by reeling in the auxiliarywinch cable. The main winch cable must be anch-ored so it will withstand the load to be placedupon it. By reeling in the boom winch cable, theend of the auxiliary winch cable will be drawnback across the ravine or river to the recoveryvehicle. The main winch cable is now in a posi-AGO 6473C 87


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tion to act as a trolley line. The vehicle to betransported should be placed under the mainwinch cable (track cable). The two large snatchblocks, part of the equipment of the recovery ve-hicle, should be placed on the track cable (fig.49). A chain may be used as a sling from eachof the two snatch blocks and secured to the lift-ing shackles at the front and rear of the vehicleto be transported. The auxiliary winch cable, at-tached at the front of the vehicle, will be used topropel the vehicle across the ravine, and the boomwinch cable, attached at the rear of the vehicle,may be used to control the forward movement(fig. 50). When the vehicle reaches the oppositebank it may be lowered by slacking off on themain winch cable. The boom winch cable and theauxiliary winch cable can now be fastened to-gether and the blocks and cables returned totransport the next vehicle. On later model re-covery vehicles, which do not have an auxiliarywinch, the boom winch would be used instead, anda heavy rope, pulled by crewmen, would be sub-stituted for the boom winch to retard the vehicle'sforward progress and to return the equipment totransport the second vehicle.Caution: Extreme caution must be exercisednot to overload the track cable. The approximate

safe load that the track cable will support at thecenter of a 200-foot span, with 5 feet of deflectionin the cable, can be determined by dividing thecapacity of the cable by 10. With the same lengthspan and 10-feet deflection, the capacity shouldbe divided by 5.88 AGO 6473C


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Figure 49. Vehicle rigged to track cable.

56. Use of a PryIn most places where a vehicle may become dis-

abled by terrain, the ground is good enough togrow timber. When pioneer tools are available,they can be used to make many wooden tools toaid in recovery. Figure 51 illustrates the use of apole to pry a vehicle out of a ditch.57. Anchoring a Wheel

When one of the driving wheels of a vehicle ismired in a deep hole, and towing equipment or awinch is not available, the vehicle may be recov-ered by tying a log to the wheel (fig. 52). CautionAGO 6473C 89


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44-

Figure 51. Pole used as a pry.

will have to exercised to apply power graduallyto prevent the wheel from spinning. If the wheelspins, the log will damage the fender and otherparts of the vehicle. After the wheel is liftedclear of the hole, log should be forced under thewheel to prevent it from falling back into thehole.58. Substitutes for a Jack

a. If an outside dual tire becomes flat, and ajack is not available, the inside dual may be runup on a small log or rock as a substitute for ajack. This takes the weight from the outsideAGO 6473C 91


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Figure 53. Substitute for a jack to removeoutside dual wheel.

wheel clears the ground (fig. 55). Set the brakeand block the vehicle securely.59. The Skid

When the driver finds himself in an isolatedarea with a flat tire or bad wheel and does nothave the equipment to repair it, a skid may beAGO 6473C 93


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FRONT OFVEHICLE

J_ 3 IN 42Figure 54. Substitute for a jack to remove tandem wheels.

GIRTH HITCH16-FT. TOW CHAIN

',.

Figure 55. Substitute for a jack to remove front wheels.94 AGO 6473C


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used if the vehicle is of the 4-wheel-drive type.The skid should be used on the rear wheel (fig.56). (Wheels can be changed from one hub toanother to accomplish this.) A pole approxi-mately 4 inches in diameter and 6 to 8 feet longshould be used. One end of the pole should beplaced above the frame crossmember near thetransmission and the other end on the ground.The pole should pass under the spring U-bolts,aline with the spring, and be lashed securely tothe spring. The pole will then support the weightof the vehicle on the side with the defective wheel.By engaging the front wheel drive, the vehiclewill move under its own power. Starting may bedifficult, but once the vehicle is moving, it willride and handle surprisingly well.60. Disabled Tandem Wheel or Axle

When a tandem wheel has a burned-out bear-ing or damaged wheel that would disable the ve-hicle or cause further damage if continued in op-eration, the axle may be tied up and made inop-erative. The disabled wheel should be movedonto a rock, log, or similar object to raise thewheel as high as possible (fig. 57). While thewheel is raised, the axle should be tied as tightlyas possible to the frame by using heavy wire ora town.hain (fig., 58). Caution should be exer-cised to prevent the chain or wire from causingdamage to the brakelines. If the bearing isburned out, or for some similar reason the wheelshould not turn, the axle shaft should be removedfrom the axle housing and the hole in the hub


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i-: i~~~i!~' ~

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stuffed with rags to keep out foreign matter. Thisexpedient will allow the other wheels to drivewhile the damaged wheel is held off the ground.This same expedient may be applied to both endsof the axle if both wheels are defective (fig. 59).When both wheels are tied up, the truck shouldnot be loaded too heavily or should be offloaded.61. Defective Differential or Final Drive

If the defect is in the differential of a 4 x 4 or6 x 6 vehicle, the propeller shaft and drive axlesmay be removed from the defective assembly and

Figure57. Raising tandem axle.AGO 6473C 97


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BRAKE HOSE ANDBRAKE HOSE SUPPORT'/=__SPRING

PROPELLER SHAFT,J'"-~---~...,~ , TO REAR AXLEFRAME SHORT CHAIN

PROPELLER SHAFTTO FRONT REAR AXLE

Figure 58. Attaching tandem axle to frame.

16-FT.TOW_CHAIN FRAME

BRAKE HOSE AND \ PROPELLER SHAFTBRAKE HOSE SUPPORT TO FRONT REAR AXLESPRING PROPELLER SHAFTTO REAR REAR AXLE

Figure 59. Disabled tandem axle.

the vehicle operated on power supplied by theother axles. When the axle shafts are removed,the openings in the ends must be covered securelyto keep out dirt and foreign matter (fig. 60).98


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62. Defective Center BearingIf the propeller shaft center bearing is defec-

tive and it is evident that operation will cause fur-ther damage, both propeller shafts to the rearaxle should be removed (fig. 61). This will pre-vent the center bearing from operating, and thevehicle may still be driven.63. Broken Tandem Spring

Occasionally, it may be necessary in the fieldto remove a broken tandem spring when specialequipment is not available to jack up the vehicle.The rear wheel of the vehicle should be drivenonto a log, rock, or

Army Vietnam Vehicle Recovery Operations

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