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Clutch Issues 101: Clutch Slipping

Clutch

A common clutch problem is slipping at the wrong time. A clutch is supposed to slip when being engaged and during gear changes, the former in order to make vehicle movement from a standstill smooth and the latter to prevent jerking and shock when shifting. This slippage happens during the clutch pedal's release, but should end once the pedal is completely released and the clutch is (supposed to be) fully engaged. If the clutch slips when the gears should be engaged, you have a problem.

Clutch slippage is most often noticed when the vehicle is under load, such as when towing, when the throttle is pressed to pass another vehicle, or immediately after downshifting when the engine is turning through the transmission at high RPM.

Most clutch slipping is caused by normal wear and tear as the clutch assembly and transmission age. Other causes could be:

  • low oil levels,
  • a leaking transmission input shaft,
  • or a bad seal allowing contamination of the clutch linings.

If a new (or mostly new) clutch is slipping, common causes are likely:

  • oil or grease contamination,
  • incorrect adjustment of the release system,
  • a bad cable adjuster,
  • a misaligned or improperly installed release bearing,
  • a block or mis-sized master cylinder or slave cylinder,
  • or a bad flywheel.

The easiest way to test for a slipping clutch is to "lug" the engine. Drive the vehicle at low speeds (under 25 mph) and in a high gear (a gear too high for the speed, such as 20 mph in 3rd or 4th gear). This kind of driving, when the transmission is under-powered by the engine, will make clutch slippage obvious to the driver.

Repairs will depend on the actual problem, but the above list of items that can be wrong will guide you through the diagnosis.

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