The acid test for catching a slipping clutch?

Dear Car Talk

Dear Car Talk | Mar 01, 1991

Dear Tom and Ray:

My 1982 Celica has 70,000 miles on the original clutch. It has not begun to slip yet, but it must be running on borrowed time. I was told by a friend that the acid test is to rev the engine with the parking brake on and let out the clutch in fifth gear. If the engine stops abruptly, the clutch is good. If it sputters on for a few seconds, your clutch has had it. Can this be correct?

RAY: Yup. Your friend is absolutely right, Brian. As weird as it sounds, this really is the right way to check a clutch. Of course, this is also a good way to see if your parking brake is slipping, so don't perform this test in front of anything you'd regret running over.

TOM: Here's why the clutch test works: As you know, when the engine is running and the car is in gear, the wheels have to turn. But if you prevent the wheels from turning (by having the parking brake on), then the engine has to stall, because its power has nowhere to go.

RAY: If the wheels don't turn and the engine DOESN'T stall, then the engine's power must be going somewhere other than the wheels. And the only place it can escape is through a slipping clutch.

TOM: But don't assume that just because you have 70,000 miles on the car, your clutch is on borrowed time. The life span of a clutch is directly related to the kind of use and abuse it gets. A good driver who doesn't ride the clutch and does mostly highway driving can get well over 100,000 out of a clutch.

RAY: On the other hand, a lousy driver (like my brother) who lives in the city can burn through a clutch in 20,000 miles. Even less if he performs this test too often!

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