Allison LCT 1000 Updates for 2003 and 2004 Model … LCT 1000 Updates for 2003 and 2004 Model ......

54 GEARS October/November 2008

Allison LCT 1000 Updates for 2003 and 2004 Model Years

Virtually all transmissions receive updates over their lifespan, and the Allison LCT

1000 is no exception. This unit experi-enced a number of updates for both the 2003 and 2004 model years.

Here are the areas that experienced major changes for the 2003 model year:• Internal wiring harness• P-3 ring gear• C-1 drum and piston assembly• C-2 piston• C-2 clutch shaft sealing rings• Valve body with new solenoids• Separator plate• Neutral safety backup switch

(NSBU)• T-6 bearing, P-3 gear and P-3 car-

rier assembly

The harness was lengthened 15mm for trim solenoid B (figure 1). In addi-tion, the trim solenoid connectors were redesigned to make sure they held together more securely. You can identify the updated harness by the red connectors for the trim solenoids (figure 2). The updated harness will fit previous models and years, and is avail-able under GM and Allison part number 29541371.

The P-3 ring gears had problems because of a chamfer in the snap ring retaining groove area. Under load, the snap ring can break or wear (figure 3). If you run into this condition, update the ring gear and snap ring with Allison part number 29537311.

A new C-1 piston has been released to improve fill times. You can identify the updated piston by the dam and the part number stamped into the casting (figure 4). The updated GM/Allison part number is 29537993. The updated piston will fit previous applications.

by Lance Wiggins


Figure 1

Figure 2

SPEAKER

54wigginsLCT.indd 5454wigginsLCT.indd 54 10/3/08 10:56:40 AM10/3/08 10:56:40 AM



This update took effect with build date S/N 6310089106 (Indianapolis) S/N 6320006057 (Baltimore).

The C-2 piston is available and is sold under Allison and GM part number 29539653. The updated piston design doesn’t have a bleed hole in it, which was eliminated to improve clutch fill times (figure 5).

The C-2 clutch shaft sealing rings have been changed from a butt cut design to a lip seal design to improve shift quality, especially in cold tem-peratures (figure 6). This change cor-responds with the C-2 piston change. The lip seals are sold under Allison part number 29538940. A basic seal-and-gasket kit with the lip seals included is available from Allison and GM under part number 29541532.

The 2004 updates were implement-ed to improve fuel economy by reduc-ing pump load, reduce pump noise at idle, and to improve cooler flow.

An updated valve body was intro-duced in 2004 that includes a line pressure solenoid (solenoid G; figure 7). The complete valve body assembly, including the auxiliary valve body and line pressure solenoid G, is available under Allison and GM part number 29541572. The auxiliary valve body alone is available under Allison part number 29539797. Solenoid G is avail-able separately under GM and Allison part number 29536833.

The updated valve body (com-plete assembly) will fit earlier units as

an assembly, although the line pres-sure solenoid (G) won’t function on 2001-03 applications. Never attempt to mix valve body and spacer plate parts between early and late applica-tions. The old valve body part number has been superseded by the updated design.

The updated valve body contains a new control main valve and springs, which are sold under Allison part num-ber 29541152 and 29541153. The valve land configuration was updated to help stabilize the valve position. The largest land is now 4.5mm long rather than the earlier 3.5mm. The updated valve and its springs will fit previous applica-tions. Never cross early and late spring and valve combinations.

Figure 5

Figure 3 Figure 4

Figure 6


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The main regulator valve will also interchange with previous applica-tions. The updated pressure regulator valve is sold under Allison part number 29542361 for all but truck applica-tions.

GMT 800 (C/K) pickups use a different pressure regulator valve; GM and Allison part number 29531323 (refer to figures 1 and 7 for identifica-tion). You can identify the valve for pickups (P/N 29531323) by the single groove machined into the valve at the end with the large land. A third pressure regulator valve was designed to update other commercial applications; you can identify this valve by the 3 grooves machined around the valve on the large land end.

The internal wiring harness was modified again in 2004 to accommo-date solenoid G; GM and Allison part number 2953972. You can identify this wiring harness by the lengthy wire to the auxiliary valve body (figure 8).

This later valve body also requires new separator plates, designed to be used on valve bodies sporting sole-noid G; Allison part number 29539793. Use figures 9 and 10 to identify the 2001-2003 and 2004-and-up separator plates.

An updated neutral safety backup (NSBU) switch has been released for all LCT 1000 applications (figure 11a and 11b). The updated switch uses only one, 12-pin connector and will be com-mon on many GM rear drive applica-tions. The new switch eliminates the metal alignment strap, and won’t fit earlier applications. The updated switch is available under Allison part num-ber 29541852 and GM part number 24221125.

The T6 bearing, P3 sun and P3 carrier were updated as a late-2003, early-2004 running product change. The load-carrying capacity of the bearing was increased in an effort to improve durability. When the bear-ing was updated, the location of the pilot groove for the bearing in the P3 sun gear also changed. In addi-tion, the machining for the undercut on the P3 carrier changed. The update was included in units built after build dates 6310220802 (Indianapolis) and 6320127996 (Baltimore).

The P3 carrier, P3 sun gear, and

Figure 7

Figure 8


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the T-6 bearing will work in earlier units if they are installed as a pack-age. The former T-6 bearing will still be available under the old part number 29531089. If the sun or carrier requires replacement on an older model unit, all the updated parts must be installed as a package. The updated Allison parts numbers are:

• P3 sun gear 29540499• P3 carrier assembly 29540500• T-6 bearing 29539501

Always double-check the part numbers before ordering. Numerous updates have occurred with many of the part numbers. GM is adding Allison part numbers as a common practice, so check the Allison part number with your local GM suppliers; you may find the part now available from your local GM source.

Transmissions are constantly in a state of change… being updated and improved over their lifetimes. Many of these changes are valuable upgrades that you should include in your regu-lar rebuilds, to take full advantage of their improved durability. Always keep an eye on your bulletins and GEARS Magazine for information about these updates; they provide you with one of the true benefits that you can offer your customers: better quality rebuilds.

Figure 11A

Figure 9: 2001-2003 Figure 10: 2004 and Later

Figure 11B


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Allison LCT 1000 Updates for 2003 and 2004 Model … LCT 1000 Updates for 2003 and 2004 Model ......

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