Author: corvair

Webmaster note: this paper was created by Mike Dawson of the Heart of American Corvair Owners Association and reprinted here with his permission.  Other HACOA technical documents are found at http://hacoa.org/index.php/technical.

Diagnosis

Any time a clutch job is undertaken to correct a problem, the cause of the problem must be identified once the transaxle is removed and the parts are available for inspection.  You may only need one part or you may need them all.  The following may be used as a guide to assist in this operation.

Chatter

1. Grease on the clutch disc is the most common culprit; however, a severe leak will make the clutch slip.  A leaking clutch shaft seal (or badly cracked release bearing shaft) will allow differential grease to be thrown from the clutch disc hub outward.  Keep in mind that a crankshaft seal will leak downward behind the flywheel and out the bottom without getting on the clutch.  The 60-63 clutch shaft seals are a smaller size than 64-69, check for the correct size; the seal must match the transmission, not the engine or differential.
2. Clutch Chatter can be caused or aggravated by a bad pilot bushing, so be sure to change this inexpensive item any time the transaxle is removed, as they take a set while in service.  Be sure and pressure oil the bushing with two fingers until the oil sweats out through the sides if you use a reproduction.
3. Rusted or damaged splines on the clutch shaft or the clutch disc can cause chatter.  These splines have to be lightly lubed in order for the disc to move away from the flywheel smoothly when released.
4. A very tall first gear ratio such as a three speed combined with a 3.27 differential and taller than stock tires will almost guarantee chatter.
5. A very stiff FC clutch cable can also make a minor chatter problem much worse.
6. Although sometimes blamed for chatter, pressure plates are seldom the culprit.  Re-using a pressure plate with an extremely rough surface could cause chatter.  Another possibility is a bent “drive strap”, which would also move the plate off center and out of balance.
7. Original clutch discs contained asbestos, which has since been banned.  The replacement material may not work as well and it is not uncommon to have minor chatter in reverse.  This chatter can usually be avoided by different pedal application or adjustment.
8. Corvair clutch discs do not have anti-chatter springs because the long shaft is flexible torsionally.  A spring loaded Vega disc can have the hub machined down and could offer a softer application.  Be sure the hub would clear the flywheel bolts and reinforcement ring, including an allowance for wear during service.  Vega discs may also be hard to find.
9. Loose bolts in the cross mount to transmission (mainly on 60-65 models), or loose or broken front motor mounts will let the transaxle jerk with clutch application.

Failure to Release Completely and Slipping

1. First, of course, is proper adjustment.  I have seen cables adjusted so badly that they were hitting the transmission mount, causing all of the free play to be in the cable and not at the release bearing.  The clutch has to release completely and you must have free place at the top of the pedal to prevent release bearing failure.  Early cables will begin to stretch just before they break, causing a failure to release situation.  Loose, worn, or broken pulleys will affect adjustment.
2. The correct parts must have been in stalled, since mismatching early and late clutch parts will cause a no release or no engagement.  A disc installed backwards will not release.  Some aftermarket discs with riveted hubs will rub on the crankshaft after they wear down, causing a no release.  That would include a spring loaded disc with a hub that was too long.
3. A bent clutch shaft can cause a no release situation.  A good pre-installation check is to install the shaft in the transaxle, then put the disc on the shaft, and turn the differential side gears while watching the disc and the end of the shaft rotate.
4. Rusted splines on a clutch/shaft disc hub can keep the disc from moving away from the flywheel when released.  An excess gear lube leak can cause a disc to “suction suck” to the flywheel briefly, and a disc can rust to the flywheel in our humidity when stored a long time.  Try to pop it loose by putting the transmission in high gear, engine off, push in the clutch and rock the car hard.
5. A disc will generally not slip until the material is worn down to the rivets with a normal pressure plate.  When installing new parts, it would be wise to bolt u p the flywheel, disc, and pressure plate, then put the assembly in a press and watch t he spring operation, since pressure plate clearance and spring pressure will vary with the rebuilder.
6. ALL original flywheels need to be reconditioned and balanced.  If you have a late flywheel surfaced, all of the area on the flywheel face must be surfaced equally or you will have no engagement, slipping or no release.  If you have a pressure plate surfaced, it may need to be shimmed to compensate or the clutch will slip prematurely.  You could surface only the mounting area on a late model flywheel to compensate for a machined pressure plate.
7. A broken pressure plate spring can cause a no release.  You can usually see that the tips of the spring fingers are at an unequal height.  Mark the parts for balance and remove the three (3) bolts and face plate to inspect the spring.  Breaks are usually at the rivet hole area.
8. Also watch for cracked release bearing shafts which expand and cause the release bearing to drag.  Check for badly worn clutch adjusting swivels. clutch cables that are stretched or repaired with the incorrect length, broken welds on the early pedal cross shaft, and numerous other weird things you have inherited from those before you!

Noises

1. A rattling or knocking noise that diminishes or goes away when you push in the clutch is a loose flywheel.
2. A quick screech that is only heard when the clutch is going in or coming out is a pilot bushing.
3. A rattling, rumbling, or knocking noise heard anytime the pedal is pushed down is probably the release bearing.
4. A clicking or light knocking coming from the clutch  housing all the time may be loose bolts in the clutch housing backing out into the flywheel or lower bolts with washers installed under them which are contacting the flywheel.

Clutch inspection and Maintenance

1. Flywheel: the three piece flywheels used in all years will loosen up and rattle, finally breaking the starter nose as well as ring gear welds when they are out of round.  They need to be reconditioned no matter how good they look.  They also need to be balanced; GM had a very large tolerance on the face and edge run out and the balance of new flywheels (face 0.020 and edge 0.010)  Check the center where it mates against the crankshaft hub; if they have been out of balance they will fret and the mating area may be damaged.  The flywheel, pressure plate, release bearing, and clutch fork pivot are a matched set for 60-63 and 64-69.  You can change the complete sets between early and late but not parts between the sets.
2. Pressure Plate: Check the ring gear for true and the condition of the teeth, check the three drive straps for any damage, check the main center spring for breaks at the stud holes, and the tips for damage from a bad release bearing.  Check for clutch material lodged under the spring.  Measure the clearance (crush) between the plate and the six (6) mounting areas with a straightedge.  Early should be .210 maximum and late should be .110 maximum.  That applies if you’re using a disc with a thickness of 0.325 (5/16″), anything thinner would require less clearance.  Balance the pressure plate with the flywheel if there is any question about its history.  When you bolt the pressure plate to the flywheel, install every other special bolt and alternately tighten in 1/4 turn increments while watching the spring fingers contract.  If the fingers show little retraction then the disc is too thin of the plate has had too much material removed during surfacing.  When the three bolts are tight, install the other three and torque to 22 ft/lbs.
3. Clutch Disc: The squeezed thickness can range from .280 to .325 (5/16″), depending on the rebuilder.  If you have an original disc, it was 0.135 for each face; a total of approximately .330 including the wave spring.  All rebuilds have to be the original 9 1/8″ Borg & Beck welded center design.  The riveted center design will hit the flywheel bolts or crankshaft hub when it wears down on late models and possibly some early models.  Make sure the splines on the disc are free of dings and check its slide on the clutch shaft.  On a used disc check the wave springs (looking at the edge) to make sure they are not collapsed or sunk into the disc material.  As noted above, check the disc for run out by putting the clutch shaft in the transaxle and turning the side gears with the disc installed on the splines.  This checks the disc and the shaft.
4. Clutch Shaft: Early shafts are smaller in diameter than late shafts from the clutch disc splines through the transmission splines.  Check the splines at both ends, check the shaft for run out as noted in #3 above, and polish the areas where the seal and the pilot bushings will work.  There are different clutch shaft lengths for different applications – if you are “making one from many”, be sure you have the correct shaft.  They can be mismatched for a disaster.
5. Release Bearing: Check it for smooth running and the face for wear.  If it appears good, it can be packed by hand with a little patience or a new one is always available.  The bearing used used with the flat finger pressure plate and flat flywheel is slightly longer with a rounded contact face.  The late style bearing is shorter and has a flat face.
6. Clutch Fork: Check for broken fingers, springs, and the fit of the pin.  The stud that it pivots on is different between the 61-63 and 64-69 flywheel/pressure plate combinations.
7. Pilot Bushing: It must be replaced when doing a clutch job; they take a set in service and lose their lubricant over time.  For removal, pack the cavity with heavy grease and use the clutch shaft or similar sized shaft to jack it our hydraulically.  Pre-oil a reproduced bushing by putting it on your finger, filling it with light oil and squeezing until the oil sweats out the sides.  Install with the chamfer side out.
8. Clutch Shaft Seal: Change this seal in the release bearing shaft and be sure the split ring that is installed in the front of the seal is sprung enough to fit snug.  Be careful removing the seal – the shaft is cast iron and will break easily.  There is a pre-64 seal and a 64-69 seal.  The determining factor is the transmission, which has to match the clutch shaft, so be sure you select the proper seal.  You could easily have a 63 transmission installed on a 64 or 65, or a 64-65 transmission on a 61-63.  If there is a drain plug on the transmission you need the small seal, as the plug indicates an early transmission.  Always test the seal fit on the clutch shaft before installing it.  Make sure there are no cracks in the release bearing shaft and dress up the are the bearing rides on, as well as greasing it lightly.  Vendors sell a steel shaft cut for two (2) seals (requires differential disassembly for the change).
9. Crankshaft Main Seal: Use only a CCP reproduction, the late replacement GM seals leaked and there were some aftermarket seals with a metal press area (they fell out when the engine was hot).  The crankshaft hub must be inspected carefully and polished where the seal mates.  If there is a groove worn in the hub, you can change housings (late/early), or use a spacer to locate the seal lips in a new area.  Press the new seal in completely and carefully making sure the spring stays in place.  Place some light grease between the seal lips, especially if you use a Viton seal as the outer lip can weld itself to the hub and then shred.  Do not use washers on the bottom two bolts and do not use replacement bolts with thick heads – the flywheel comes very close to them.  The original bolt lengths were 7 at 1-3/8 shank, 2 at 1-5/8 shank.  Torque to 30 ft/lbs.  Once the housing is back on the engine, inspect the seal lip-to-crankshaft area for any lip distortion.
10. Lubrication: The clutch disc has to slide on the splines, so lightly lube this area.  DO not grease the pilot bushing; oil as noted above.  Lightly lube the crankshaft hub seal area and fill the seal lip cavity, clutch shaft seal area, release bearing shaft, fingers on the fork, face of the release bearing, pivot, and the pin where the pull rod attaches to the fork.
11. Flywheel and Clutch Installation: Use thread sealer on the flywheel bolts.  Clean and add sealer to the crankshaft keyway and around the hub to crankshaft line, install the reinforcement ring and the correct bolts, and toque to 40 ft/lbs.  Install a welded hub clutch disc with the “flywheel side” installed towards the flywheel.  As a double-check use your fingers to twist the disc on the flywheel to confirm the hub does not rub on the crankshaft.  Use the special shouldered bolts with lock washers on the pressure plate.  The fingers of the fork go inside the bearing sleeve and be sure the small fork is fitted on the pivot.
12. Differential: As long as you are this close, make a couple of checks.  Separate the transmission and check the internal splines in the differential pinion shaft by using a flashlight.  This is a common wear are and if they are more than 50% missing you should consider replacement.  Pull the top cover and check the fit of the pinion gear on the shaft – look for a loose gear and play in the shaft at the bearings and consider how much wear shows on the pinion gear; different rations have different thicknesses.  Check for the proper pre-load adjustment on the pinion bearings.  You may want to change the gear oil with the 64-69 units are out of the car, since they do not have drain plugs like 60-63 models did.  If you drive your care in cold weather you may want to consider synthetic lubricant to aid in shifting.

Installation Tips

1. Double check before attaching transaxle to engine.  Think back, did you torque all bolts, check the slide of the disc on the clutch shaft splines, look for clutch shaft and disc run-out, change the  clutch shaft seal and pilot bushing (chamfer out), install the disc with the words “flywheel side” towards the flywheel, check the clutch fork installation and release bearing movement on the shaft.
2. Cut two pieces of 3/8-16 threaded road about 5 inches long and saw screwdriver slots in one end.  Use these as guide pins  and once the transaxle is mated to the engine you can remove them with a screwdriver and install bolts.  Cut screwdriver slots in the ends of the mounting bolts to aid in installation (this can be done prior to removal if there is enough of the bolt end sticking out).  Do not pull the transaxle onto the engine by tightening the mounting bolts – the transaxle must slide onto the engine completely.  The reason for difficulty in attaching the transaxle is almost always because the angle is wrong.  Inspect the lineup carefully and even measure to see if the assembly is square.
3. Once the transaxle is bolted up, check the movement of the clutch fork to make sure it was not displaced during installation.  It is easier to add any lost gear lube to the transmission or differential at this point before installation.  With an early model, plug the side seals with round turn signal flashes, gas tank floats, etc, until the unit is ready for axles.
4. Before the installation of the transaxle, this is the time to address the “as long as it’s out” itmem such as heater hoses, rubber fuel line connector, blower motor, motor mounts, U-joints, rear wheel bearings, heater box and cables, harmonic balancer, positive battery cable brake lines, engine seal, etc.

Clutch Job Tools

If you plan on doing more than one clutch job, you consider acquiring or making a few special tools. If one job is your limit, you may be able to borrow a couple of items to help the job go smoother.  The following are my favorites:

• You need a quality floor jack and a cradle to lower the drive train and move it around as necessary.  Making a cradle out of wood is cheap and easily modified as you see fit.  Keep safety in mind with good jack stands, wheel chocks, etc.  Removing the enging and transaxle as a unit eliminates telescoping the clutch shaft and possibly bending it or breaking the the release bearing shaft if you leave either the engine or transaxle in the car.
• If you can acquire or borrow a cut off Corvair clutch shaft you can use it to remove the pilot bushing and for alignment of the new clutch disc.  Any donor shaft will do as the clutch disc end is the same for all.
• Two guide pins as mentioned above for alignment of the transaxle to the engine.
• Purchase PVC fittings from the plumbing department that can serve as press devices for both removal and installation of crankshaft seals.
• Make a balance tool out of a spare early model engine top cover with a used fan bearing.  Take a flywheel to a machine shop and have them slightly turn down the bearing to where the flywheel just fits up against the flange.  Weld two 3/8″ nuts on the bottom of the fan bearing flange under two  opposite holes.  Remove both seals and clean out the bearing in order to use very light oil of WD40 during balancing.  Install the bearing back in the cover and mount the cover perfectly vertical in a vice or on the wall.  Bolt the flywheel to the bearing and you can now check centering, run out and balance.  I like using an early model since they take less machining and because late models are best used as fan bearings!