Tech Area

Clutch Diagnosis

Question: I am having clutch problems. Please help!

Answer: There are basically two potential problems with any clutch system. 1st is "no pull" and 2nd is no disengagement. "No pull" is always mechanical, and is usually the disc worn down or the friction material missing. Requires replacement. Smart thing is to also replace the plate and the release bearing, since it is so much work to remove the transaxle. Worn disc is caused by long term use (slippage), abusive use(slippage), or a mechanical malfunction (slippage), which would be: release bearing shaft binding in its bushings, or release bearing binding on its slide collar. Both conditions result in a partially applied plate that allows slippage (wear). All clutch replacements should include inspection/correction of these conditions, or premature wear will happen. No disengagement is trickier, since this can be caused by hydraulic or mechanical malfunction. Start at the begining, the pedal. It should be an inch higher then the brake. If not, then look for the standoff bracket (the squared U riveted to the pedal) to be bent. Use will bend it toward the center and toward the rear of the car (away from the clutch master cylinder). You need this inch for a full hydraulic push of fluid. This bracket can very often be bent back into shape with a large set of channel lock pliers. Much maligned pedal is seldom bent. If there is slack at the top of the pedal, until resistance is felt, then there is also not enough push. This is usually caused by the master cylinder groument missing, or the pushrod being bent. Make sure pushrods offset hole is in the "up" position. While in this area (upside down on the drivers floor), pull the master cyl boot loose and check for any moisture. If any is found, then master cylinder rear seal is leaking. Replace it, unless you want a 50/50 chance on rebuilding it. Bench bleed before installing. If all is OK, then slowly have the clutch pedal depressed, while watching the resevoir fluid (cap off). If fluid level rises any at all, then check valve in master cylinder is allowing some pressure to bypass, and you will not have a full disengagement. This completes the mechanical and hydraulic inspection at the front.

In the rear, clear area above the slave cylinder of air intake tubes. Have the clutch slowly depressed again. Some movement of the slave cylinder is normal, but you are looking for two things. Broken mounting bracket, and length of pushrod stroke. (At this point we have removed oil pump drive shafts, drum brake adjusters, valve pushrods, various modified bolts, and a piece of broomstick, all in an attempt to get the last 1/16 of stroke.) Stroke should be at least 15/16". 7/8 will not allow full release. We measure this with the pedal depressed, tape measure against clutch lever, then read tape measure "backwards" as pedal is released. Do this several times, as it is easy for tape to slip. If measurement is good, then so are hydraulics. If not, then pull slave cylinder boot loose to check for moisture. If found, replace slave cylinder, or the 50/50 rebuild rule applies here also. If no moisture is found at the front or rear, you can reasonably expect that someone has replaced a unit, and not done a "proper" bleeding. But, wait a minute! 84-86 4 spd and 5 spd Fiero's (except 86 getrag) were delivered with a stamped steel clutch lever that has a plastic block that the slave cylinder pushrod pushes against to rotate the release bearing shaft. This lever can crack where it is clamped to the shaft, and the plastic block can "push through". Many expensive clutch jobs have been done, when only this lever was the cause of" no disengagement". Replacements, 87-88, and all getrags are cast. Further disengagement problems will be inside the bellhousing, and require removing the transaxle. On 4 spd cars, a broken/bent release bearing fork will usually make much noise and make the clutch pedal feel as though it has a brick under it. It could be on 4 spds and will be on both 5 spds, a broken disc dampner spring, that has a piece lodged in the plate release springs, that make it feel that you are pushing against a brick. This completes mechanical and hydraulic inspection in the back.

Our bleeding procedure is not found in Clymer, Chilton, Haynes, or Helms (Pontiac) service manuals. Therefore, must not be authorized, but has worked without fail for over 10 years. Jack car from front about 1 foot (until master cyl is above height of slave). Remove resevoir cap. Open (not remove) bleeder on slave cyl. Gravity feed 1/2 pint of hydraulic (brake) fluid. If gravity doesn't start fluid movement, SLOWLY depress clutch pedal until fluid starts to move. After 1/2 pint has gone through system, close bleeder. Needle nosed vise grips work best (especially 6 cyl, which may require removal of slave cyl from bracket). Clamp vise grip pliers to slave cyl pushrod. Pull pushrod into the barrel of the slave cyl, while at the same time "cracking" the bleeder. The bleeder is at the wrong end of all three different slave cylinders. Air can be trapped at the end where the pushrod is, and must be pulled to the bleed valve. Check resevoir after first "pull" (can be nearly empty). We repeat this 5 times, or until no more bubbles appear. After 6 times, if there is still a bubble, Start over at the clutch pedal. Step 1, along time ago. Caution: do not shave (cut, machine) the flywheel. Hydraulic clutch systems typically have 0 to .003 clearence between the face of the release bearing and the fingers on the clutch plate. Removing material from the flywheel will move the plate that much further away from the release bearing, perhaps causing a non-release condition. Remanufactured clutches will usually have as much as 1/16" variation in the height of the plate fingers. Also resulting in a non-release condition. If the release bearing fork is too worn, then the same applies. Hydraulic clutch systems are called self adjusting, because they can only move a predetermined amount of fluid. The spring pressure of the plate will override the hydraulic pressure, so, extending the slave cyl pushrod length will not "adjust" the system.

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