DIAGNOSING CLUTCH PROBLEM

A motor vehicle clutch normally provides depend- able service for thousands of kilometers. However, one vehicle’s clutch might last 100,000 kilometers, while another’s could fail in only 50,000 kilometers.

Stop and go, city traffic will wear out a clutch quicker than highway driving. Every time a clutch is engaged, the clutch disc and other components are subjected to considerable friction, heat, and wear.

Driver abuse commonly causes premature clutch troubles. For instance, “riding the clutch” (over- slipping clutch upon acceleration), resting your foot on the clutch pedal while driving, and other driving errors can cause early clutch failure.

Verify clutch problem

After talking to the service writer or customer about the problem, verify the complaint. Test drives the car and makes your own decisions about the clutch troubles.

Check the action of the clutch pedal. Listen for unusual noises. Feel for clutch pedal vibrations. Gather as much information as you can on the operation of the clutch.

Use this information, your knowledge of clutch principles, and a service manual troubleshooting chart (if needed) to decide which components are at fault. You must determine whether the clutch failure was due to normal wear, improper driving techniques, incorrect clutch adjustment, or other problems.

There are several types of clutch problems: slipping, grabbing, dragging, abnormal noises, and vibration. It is important to know the symptoms produced by these problems and the parts that might be the cause. Then, you will have a good idea of the repairs needed to permanently correct the clutch problem, Fig. 17-14.

Clutch slips under load

Typically, clutch slippage is noticed when the engine races (engine rpm increases quickly) without an equal increase in the car’s road speed. This is caused by the clutch friction disc sliding between the flywheel and pressure plate. Clutch slippage usually occurs as the car is accelerated from a standstill, when shifting, or when under a heavy load (climbing a hill, or pulling a trailer for example).

To test the clutch for slippage, set the emergency brake and start the engine. Place the transmission or transaxle in high gear. Then, try to drive the car forward by slowly releasing the clutch pedal.

A clutch in good condition should lock up and stall (stop) the engine immediately. A badly slipping clutch may allow the engine to run, even with the clutch pedal fully released. Partial clutch slippage could allow the engine to run momentarily before stalling.

Fig. 17-14. Study types of problems that can develop in a clutch. Keep these problems in mind during clutch diagnosis and repair.

 

Never allow a clutch to slip for more than a second or two. The extreme heat generated by slippage could damage the flywheel or pressure plate faces.

Figure 17 Fig. 17-15. Without free play in clutch release mechanism, fork could push throw-out bearing into pressure plate, even with clutch pedal fully released. Clutch slippage could result. (Volvo)

 

Some common causes of clutch slippage include: a maladjusted clutch, binding clutch linkage or cable, clutch disc wear, broken engine mount, oil or grease on clutch disc (leaking oil seal).

Improper clutch adjustment can cause slippage by keeping the throw-out bearing in contact with the pressure plate in the released position. Even with your foot off the pedal, the release mechanism will act on the clutch fork and throw-out bearing. This can make the clutch slip under load.

Free travel is the distance the clutch pedal or clutch fork moves before the throw-out bearing acts on the pressure plate. Free travel is needed to ensure complete clutch engagement. Some vehicle makers recommend checking clutch free play at the clutch fork, Fig. 17-15. Others recommend checking pedal free play, Fig. 17-16.

A binding clutch release mechanism can also cause clutch slippage. Inspect release mechanism parts. Check for rusted, bent, misaligned, sticking, or damaged components. Wiggle the throw-out lever (fork) to check for free play. See Fig. 17-17.

A broken engine mount can cause clutch slippage by allowing engine movement to bind the clutch linkage. Under load, the engine can lift up in the engine compartment. This can shift the clutch linkage and push on the clutch fork.

If clutch slippage is NOT caused by a problem with the clutch release mechanism, then the trouble is normally inside the clutch housing. You would need to remove the transmission and clutch components for further inspection.

Figure 18 Fig. 17-16. Clutch pedal free play is distance pedal moves until throw-out bearing touches pressure plate.

 

Grabbing (chattering) clutch

A grabbing or chattering clutch will produce a very severe vibration or jerking motion when the car is accelerated from a standstill. Even though the driver is slowly releasing the clutch pedal, it will feel as if the clutch pedal is being rapidly pumped up and’ down. A loud banging or chattering sound may be heard as the car body vibrates. Normally, clutch grabbing or chatter is caused by problems with components inside the clutch housing (friction disc, flywheel, or pressure plate). The clutch will usually require disassembly.

Note, however, a broken engine mount, as discussed earlier, can also cause erratic clutch linkage operation. Check the engine mounts before removing the clutch.

Dragging clutch

A dragging clutch will normally make the trans- mission or transaxle grind when trying to engage or shift gears. Something is causing the friction disc to stay engaged to the flywheel. This keeps the transmission input shaft spinning, even when the clutch is disengaged. Severe clutch drag will make the car move forward whenever the engine is running and the transmission is in gear.

One of the most common causes of a dragging clutch is too much pedal free travel. With excessive free travel, the pressure plate will not be fully released when the pedal is pushed to the floor Fig. 17-16. Always check clutch adjustment when symptoms point to a dragging clutch.

A dragging clutch can also be caused by a warped or bent friction disc, oil or grease on the friction surfaces, rusted or damaged transmission input shaft spines, or other problems inside the clutch housing.

Abnormal clutch noises

Various noises can be made by faulty clutch parts. To diagnose noises, note when the clutch noise is produced. Does the sound occur when the pedal is moved, when in neutral, when in gear, when the pedal is held to the floor? This will help determine which parts are producing the abnormal noises.

A worn or unlubricated clutch release mechanism will produce odd sounds (squeaks, clunks, scrapes) whenever the clutch pedal is moved up or down. With the engine shut off, pump the clutch pedal while listening for the sound.

If needed, have a helper work the pedal while you locate the sources of the noise. Use a stethoscope or section of vacuum hose as a listening device. Clean, lubricate, or replace parts as required.

Sounds from the clutch, when the clutch is initially ENGAGED, are normally due to friction disc problems. The lining could be worn, causing an abrasive, metal-on-metal grinding sound. If the friction disc damper springs are weak or broken, a knocking or rattling sound may be produced.

Abnormal sounds from the clutch only when the clutch is DISENGAGED, may be from a faulty throw-out bearing. It may be dry and badly worn.

A worn pilot bearing (or bush) in the crankshaft may also produce noises during clutch disengagement. The worn pilot bearing can allow the transmission input shaft and clutch disc to vibrate up and down. Abnormal sounds, only heard in NEUTRAL, that disappear when the clutch pedal is pressed, are usually caused by problems inside the transmission. The manual transmission input shaft is still spinning whenever the clutch is engaged. However, the input shaft stops turning when the clutch is disengaged. The front input shaft bearing could be worn, for example.

Pulsating clutch pedal

A pulsating clutch pedal is normally caused by the run out (wobble or vibration) of one of the rotating components of the clutch assembly. Slight up and down movements of the clutch pedal can be felt with light foot pressure. The flywheel may be warped. The clutch housing might not be properly aligned with the engine. The pressure plate release levers could be ber1t or maladjusted.

Normally, to correct a pedal pulsation problem, the clutch must be removed and inspected. Then, the faulty or misaligned parts can be replaced or repaired.

Clutch pedal hard to depress

A stiff clutch pedal results from a problem with one of the parts relating to the clutch release mechanism: linkage, cable, hydraulic components, over-centre spring, clutch fork, throw-out bearing, or pressure plate. One of these parts is resisting normal movement and is increasing the amount of pedal pressure needed to release the clutch.

Check the action of the clutch release mechanism. Look for binding parts or parts needing lubrication, Fig. 17-17. Check the over-centre spring. If it is broken or stretched, increased pedal effort will be required.

Also, inspect the clutch fork. If it has fallen off its pivot ball or bracket, the clutch pedal can be very hard to push down. Normally, bell-housing removal would be needed to reinstall the clutch fork or repair the pivot.

 

KNOW THESE TERMS

Asbestos, Clutch adjustment, Bleeding, Trans- mission jack, Clutch pilot shaft, Clutch slippage, Clutch pedal free travel, Clutch chatter, Dragging clutch, Stiff clutch pedal.

Figure 19 Fig. 18-5. If gear wear is irregular, check shafts for run out. Lathe type support or V-blocks will hold shaft. Use dial indicator to measure run out. Reading indicates a worn or bent shaft. (Honda)

 

Fig. 17-11 Always check clutch linkage when clutch pedal action is faulty; Look for bent rods, worn bushings, missing springs, unlubricated bearings, damaged bell crank and other trouble. (Typical)

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