Clutch Diagnostics

Technical Answers to your Questions

Question the customer. When did they first notice the problem? When does it occur? When is it most noticeable? What is the service history? Do they tow anything with the vehicle? Take a test drive with the owner and observe driving habits. Do they ride the clutch? Down shift at high speeds? (What problems might this cause?) Do they coast downhill? (What might this cause?)

During a test drive: Where does the clutch release and engage? Is it a simple free play adjustment? How would you know?

Listen for unusual noises while driving. What is indicated by gear clash in all gears?

What is indicated by gear clash in only some gears? What is indicated by a growling noise when you begin to disengage the clutch? Is the clutch disengaged with the pedal up or down?

Shop test for slipping clutch: engage park brake and depress service brake. Shift the car into high gear and slowly release the clutch. If the engine rpm decreases, but does not stall, the clutch is slipping. Stop the test immediately.

Clutch Chatter (shaking or shuddering when clutch is engaged): Caused by broken engine or transmission mounts, glazed disk. (What causes disk glazing?) Other causes of chatter are: uneven engagement caused by worn front bearing retainer, bent clutch disk, loose trans or bell housing mounting bolts, worn pilot bearing (misalignment of transmission input shaft)

What does a growling noise indicate when the vehicle is in neutral, clutch engaged, with engine running? Transmission input shaft bearing, pocket bearing, or countershaft bearings.

What are the three possible sources for contamination for a clutch disk? Trans input seal, engine rear main seal, slave cylinder. Locktite flywheel bolts, check for missing dowels.

Dragging clutch (not disengaging, or slow to disengage) caused by improper free play adjustment, warped disk or pressure plate, loose disk facing, defective release lever.

To test: put the vehicle in neutral with engine running, disengage clutch and attempt to shift into gear. If gear clash occurs, then clutch is dragging.

Pedal pulsation: slight pulsations are normal. Pulsation can be felt when the pedal is depressed. Can be caused by: broken, bent or warped release levers, misaligned bell housing, warped pressure plate, flywheel, or disk.

Binding clutch: linkage problems, worn transmission front bearing retainer, bad pilot bearing, damper spring fell out, clutch facing loose, damaged splines on input shaft.

Free play adjustment: Check linkage for wear whenever free travel is adjusted. If linkage is worn, free travel adjustment will be incorrect. Some of the pedal travel will be used to compensate for wear, giving a false adjustment. On vehicles with linkage type clutch controls, adjust free travel if it falls below 1/2 inch.

Free play adjustment is made at release lever to obtain about 3/16 in. clearance between the TO bearing and the clutch fingers. This should provide you with greater than 1/2 in,

but not more than specification. If travel is greater than spec, suspect worn linkage. Linkage should be lubricated regularly with chassis grease.
Cable type clutch controls may or may not require adjustment. Some are self adjusting.

Hydraulic clutch controls: Use only recommended fluid. Usually brake fluid. Fill only to level line. Overfilling can prevent the clutch from engaging completely and cause slippage. Fluid level will rise as disk wears, and also as fluid hears up.

What can cause incomplete disengagement in a hydraulic clutch? Failed seals in master cylinder or slave cylinder, air in system. Follow procedures and specifications. Some hydraulic clutch systems require an adjustment of slave cylinder push rod length, and all will require a pedal stop adjustment.

Bleeding the system can be very difficult. Never open the system if it is not necessary during a clutch repair.

Sometimes the manufacturer will give a pushrod travel specification that can be measured with a tape measure. If it is less than spec, suspect faulty master cylinder.

Clutch dust: may contain asbestos. Never blow with compressed air. Vacuum out or clean housing with solvent. Asbestos is only dangerous in its suspended state.

Pressure plates. Use only special pressure plate to flywheel attaching bolts. Tighten evenly in a star pattern to avoid distorting the pressure plate cover. Remove a pressure plate in the same manner. Always mark pressure plate to flywheel orientation to maintain balance.

Flywheel: Always mark flywheel to crankshaft orientation to maintain balance. Check flywheel run out. Inspect for how spots and scoring. Resurface if necessary.

Pilot bearings: Remove with puller or slide hammer, or by filling the cavity behind the bearing with grease, and driving in a shaft through the center of the pilot bearing.

Pilot bushings: Usually more difficult to remove. May be removed with a puller, may require some chisel work, or use of a deburring tool (carbide bit) to remove some material from the I.D. of the bushing. Be careful not to go too far, and remove material from the bushing bore.