How to know when clutch's end is near

Q: Is there a way to know when your clutch is about to go out? A friend drove my car and told me he thought mine was about gone. Can you also explain what it takes to have the clutch replaced? How long are they supposed to last?

A: If your clutch is on its last legs, there may be noticeable symptoms.

Let's look at the two significant ways a clutch can fail, and see where yours might fit in. A clutch can either slip or fail to disengage.

A slipping clutch is typically caused by a worn clutch disc, the part containing friction material. As the disc wears thin, one may notice the clutch engages (begins to move the car from a stop) as the clutch pedal reaches the top of its travel, rather than about the halfway point or lower.

The clutch may also slip on a steep hill - the engine will speed up more than it should for a given vehicle speed. A failed pressure plate can also cause clutch slippage.

Clutch chatter is a less critical engagement issue. An overheated clutch, or one contaminated with fluid, may chatter during engagement.

This is annoying, but unless severe, isn't a significant problem. Being careful engaging the clutch, particularly when starting the vehicle on steep hills is the best way to avoid this fault from occurring.

The more briskly a clutch is engaged (within reason), the less wear and heat will be produced.

The other common clutch failure is improper disengagement. The noticeable symptom here is difficulty engaging gears when stopped, or gear-clashing when shifting.

This can be caused by a failed pressure plate - the part that clamps and releases the clutch disc to the engine's flywheel - or a linkage problem. Most modern clutches use a hydraulic system to transfer motion from the clutch pedal to the clutch mechanism.

A leak in a master or slave cylinder, or in a line connecting them, could result in a loss of fluid and improper release function. Older vehicles use cable or lever linkages, which can sometimes bind, wear or break.

An additional disengagement problem may be a worn or noisy throw-out (release) bearing. This part transfers the push of the clutch fork to the rapidly spinning pressure-plate fingers.

The clutch may grab and release fine, and will continue to do so until the bearing finally comes apart. In rare cases, a problem could also develop with the clutch fork and/or fork pivot. These parts transfer motion from the external linkage to the throw-out bearing.

Renewing a clutch involves removing and reinstalling the transmission and the clutch components.

A replacement clutch kit typically contains a clutch disc, pressure plate and throw-out bearing. It's a good idea also to resurface the flywheel, as its friction surface may have become distorted.

Depending on the vehicle, clutch replacement can take five hours to 15 hours, plus perhaps $200 to $800 for parts.

Clutch life really depends on driving habits and terrain. With gentle use, a clutch may last 150,000 miles, while a vehicle driven daily in San Francisco, or by a teenager, may expire at 30,000 miles.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him e-mail at under-the-hood@earthlink.net; he cannot make personal replies.