Clutch Fork Bushings

Solving The Fiero Clutch Problems

Fieros with standard transmissions, particularly early models, have clutch problems because: the clutch cross-shaft (fork) bushings are too tight!

You know something is wrong with your clutch when you experience one or more of the following symptoms:

  1. clutch pedal gets hard to push
  2. transmission begins to grind going into reverse
  3. odd clutch release points (point where the car begins to move varies, sometimes at the top of the pedal travel, sometimes at the bottom, other times in the middle)
  4. clutch fails to engage when cold (you push in the clutch, select a gear, let out the clutch and nothing happens. Several seconds or even minutes later, it engages and you drive off)
  5. transmission will not go into gear while engine running. (If you turn off the engine, engage 1st gear, you can then drive off. Gear changes are made on the synchros of the transmission, not the clutch release.)
  6. clutch slips (Doesn't drive at all! Even a new clutch may not last 60 seconds while slipping!)
  7. release bearing rattles. (Release bearing may normally make a slight noise when pedal depressed but stop when pedal released)
  8. sometimes the release bearing presses against the pressure plate at all times. (The bearing is not designed to run constantly. When it fails, it will burn a hole clear thru the pressure plate spring fingers. You will not be able to disengage the clutch if that happens.)

When GM engineers specified the clutch cross-shaft bushing clearances, they evidently were not cognizant of some or all of the following points:

  1. GM engineers assume that both bushing holes in the bellhousing are drilled in a perfectly straight line. In practice, perfection is seldom possible. If one or both holes, are off even a few millionths of an inch, the shaft may bind and the clutch slips.
  2. Temperature distortion. Metal expands and contracts with temperature changes. The bellhousing distorts slightly when subjected to temperature extremes. When the shaft binds, the clutch slips.
  3. Bolting the bellhousing to the engine can cause distortion. Binding=Slipping.
  4. The bellhousing is a hostile environment, internal parts are not bathed in oil, as inside a transmission. Dirt, from a normal wearing clutch disc, gets in the bushings. You guessed it--the shaft binds and the clutch slips.
  5. There are no dust seals inside the bellhousing. The designers appeared unaware of clutch dust. There is however, an external dust seal on the outer bushing. This is to prevent dust, engine compartment dust, from entering. In reality, it just makes it harder to grease the outer bushing.
  6. The bushings must be pressed in. This causes a slight compression of the bushing, causing the shaft to bind and the clutch to slip.
  7. Production tolerances. When GM orders a part, they specify its design limits. They do not ask the supplier of what tolerances he is capable. GM demands a perfect part and that is impossible. Normal production variances cause, on occasion, a tight fit and a slipping clutch. This could easily be avoided if GM were to specify tolerances based on the real world.
  8. If you have a tight fit and clutch dust, you must have a grease fitting for each bushing. There are none.

The entire clutch system appears to be a one-off show car design, never intended for production, because:

  1. there is no adjustment anywhere for pedal free play
  2. $200 worth of hydraulic parts are used when a $25 clutch cable would have been much more sensible.

Remember that the Fiero project was a design "exercise," viewed as an interesting project or "busy work" by the designers. When the project WAS scheduled for production, it was canceled 3 times. When the 4th go-ahead was given, the designers weren't about to risk embarrassment and another termination of the project by pointing out "glossed-over" designs. These people are all gone now, so their strategy worked for the short run...but may the "Ghost of Fieros Past" haunt them!

Back to tight bushings: When the clutch release cross-shaft binds because of tight bushings, heat, mis-alignment, clutch dust, etc., the clutch lever and the clutch pedal are both overloaded. The lever flexes and cracks, the pedal bends--and eventually, the clutch slips!

It should be obvious by now that just REPLACING THE CLUTCH doesn't solve the problem. You must ALSO add clearance to both bushings on the clutch release cross-shaft and, possibly, to the clutch-release bearing shaft (the input shaft retainer.)

The Temporary Fix!

Early clutch failure can sometimes be postponed. This is how to get by without replacing the clutch, if you're lucky!

You must lubricate the outer bushing (now and often). You should squirt oil between the clutch lever and the bushing dust seal. The oil should work its way in. If it doesn't, remove the lever, pry out the seal and squirt in the oil. Skip this step and you can go right to the $800 clutch job.

Why is this a temporary cure? Because you can't lube the inner bushing without removing the transaxle!

The Ultimate Fix!

When your luck runs out, you will need a new clutch--and you must add clearance in the proper places or the same problem will occur again.

The process of adding more clearance will extend a normal clutch job about a half hour. A mechanic familiar with the procedure will be able to do it much more quickly, probably about 10 minutes extra time.

You should talk directly with the mechanic, not just to the service writer, and explain what is needed. Since the procedure is a little out of the ordinary, a $10 tip before he starts and another when the job is done (and he can prove there is sufficient clearance) may be in order. Insist on seeing the final clearance check (while everything is still apart).

Fix It Right The First Time - Add Clearance For The Permanent Cure

  1. Remove the release bearing
  2. Rotate the clutch lever (outside the transaxle) back and forth while you slide the clutch-release cross-shaft out.
  3. Polish the clutch-release cross-shaft with a 1" by 12" strip of emery cloth at the points where it fits into the bushings. Wrap a piece of stationary around the shaft (Cut out the guide on the back of this page) and try to slide the shaft back into the bushings. If it won't fit, continue polishing until it does! Be sure it slides into both bushings with the paper before final assembly. That will give about .006" clearance at both bushings!
  4. Clean the bellhousing to remove all clutch dust. Grease both bushings with the best grease available.
  5. Check clearance on the input shaft retainer (the clutch release bearing slides back and forth on this part.) This should also be about .006" clearance (use the same "paper" trick to determine it.) If it needs more clearance, either hone out the clutch release bearing (with a brake cylinder hone) or use emery cloth on the input shaft retainer. When you install the release bearing, be sure to pack the release bearing groove (where it slides on the shaft) with high-temp grease, prior to assembly.)

Remember to remove the paper before assembly!

You should still squirt oil on the outer bushing every 3-6 months. With the larger clearances and lubrication it will take a lot longer for the same clutch problem to occur again, if ever.

From: Fiero Secrets, the newsletter of Matt Gruber's Worldwide Fiero Club (now defunct)

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