McPherson Strut Service and Diagnosis

Consumer Auto Suspension Lecture 2

How McPherson Struts Work

• Struts combine coil spring, shock, and upper control arm

• Upper bearing provides a place for the strut to swivel

• Helps keep wheel in contact with the road

• How the strut is attached to the car is critical for wheel alignment

Lower Control Arms Function

• Connect frame to steering knuckle

• Has bushings on one end, a ball joint on the other

• Uses a rubber bumper to prevent metal to metal contact

Steering Knuckle Function

• Connects lower control arm to strut

• Swivels on ball joint and upper bearing

Stabilizer Bar Function

• Connects left and right lower control arm

• Connected to vehicle body

• Reduces body roll

Strut Rod Function

• Connects lower control arm and frame

• Holds control arm in position, keeps wheels in alignment

Diagnosing Noise Problems

• Loose mountings• Loose or damaged

struts• Worn or damaged

ball joints• Worn control arm

or stabilizer bushings

Diagnosing Ride Height Problems

• Damaged or broken parts

• Broken or fatigued springs

• Misaligned body mountings

Diagnosing Body Roll Problems

• Bad struts

• Worn stabilizers

• Worn control arm bushings

• Worn ball joints

Control Arms Inspection

• Raise vehicle, inspect for signs of damage

• Pull and push wheel to check for ball joint wear

• Use pry bar to inspect for arm bushing movement

MacPherson Strut Inspection

• Check for oil leaks, bent piston rod or other parts

• Check springs for damage or breaks

• Turn wheel from stop to stop and listen for noise

• Check shock for proper operation

Steering Knuckle Inspection

• Check for damage

Stabilizer Bar and Links Inspection

• Check for damage and broken/missing bushings

• Check for bent parts

• Check for loose bolts

Strut Rod Inspection

• Check for bending

• Check frame bushings

• Check for loose bolts or nuts

Check Connections to Other Parts

• Tighten bolts and nuts

Lubrication

• Use recommended grease

• Follow lube schedule in the owners manual

Suspension Parts are Not Repairable

• Repaired suspension parts are NOT SAFE!!!

• Repaired suspension parts wear out much quicker

Front End Alignment

• Needed after the control arm, steering knuckle or strut has been changed

• Not necessary after stabilizer (sway bar) replacement

Stabilizer Bar Replacement

• Unbolt sway bar brackets

• Unbolt link assemblies and replace

Strut Rod Replacement

• Raise and support vehicle

• Unbolt from the frame

• Unbolt from the control arms

• Remove bolt from lower control arm

• Install new strut rod, bolt to frame, and control arms

• Reinstall bolt in lower control arm

• Torque to specifications

MacPherson Strut Replacement

• Raise and support vehicle

• Mark adjustment cam on lower attachment point

• Unbolt lower and upper attachment

• DO NOT remove shock nut in center

• Remove strut and replace

• Replace all one-time fasteners

Lower Control Arm Replacement

• Raise and support vehicle

• Remove wheel and support

• Disconnect strut rod and stabilizer bar

• Separate ball joint, unbolt from frame

• Replace ball joint, bushings

• Install new part

That Concludes Suspension Lecture 2