Transmission Clutch Diagnosis
Diagnosing clutch noise and slippage is pretty straight forward. Once a technician understands the different parts and theory it’s easy to locate the culprit. Typical symptoms include clutch slipping, chatter, and dragging. Here are a few symptoms, tests, and the relevant parts to look out for:
Slippage: This is by far the most common problem. To diagnose this problem set the emergency brake. Now start the engine and depress the clutch pedal. Place the transmission in high gear, rev the engine to 2500 RPM and slowly release the pedal. If the engine does not stall the clutch is slipping. Always check the cables, hydraulics, and motor mounts first as an over adjusted cable, blocked master cylinder compensation port, or a broken motor mount can cause slippage. As mileage increases the clutch disc will wear and this will cause slippage. An oil soaked clutch disc will slip as well as a weak or warped pressure plate.
Chatter: Clutch chatter is an excessive vibration felt just as the pedal is being released and the clutch is beginning to engage. To test for this condition set the emergency brake, depress the clutch pedal and rev the engine to about 2000 RPM. Slowly release the pedal so you can feel when the clutch starts to engage. This is the point a clutch will begin to shudder. Clutch chatter is typically caused by glazed or oil contaminated clutch facings. The engine and transmission mounts and alignment dowels should be checked as misalignment will cause major clutch chatter as well as damaging parts.
Bearing Noises: Bearing noises in a clutch system are easily distinguished by running a few simple tests. Start the engine and leave the transmission in neutral. If a transmission makes noise when it is in neutral it is often a worn input shaft bearing. Now depress the pedal until the clutch just engages. This is the point where the release bearing is just contacting the pressure plate fingers. If you begin to hear a squealing sound this is likely a worn release bearing. If a whirling noise is present when the clutch pedal is fully depressed it is probably the pilot bearing.
Clutch dragging is when the clutch is not releasing completely. This is typically caused by a misadjusted brake pedal, warped disc / pressure plate, or misadjusted linkage. Note that a warped disc, pressure plate, or flywheel will also cause pedal pulsation. If you feel the pedal moving up and down while depressing the pedal there may be a warped or misaligned part.