Corvair Forum

I just replaced the bellhousing seals and mated up a different 4-speed tranny and diff with a fresh pilot bushing and throw-out bearing, refabbed clutch disk, and filled it with Redline MT-90 Gl-4 gear oil. No more leaks, but I am getting a shaking when I let off the gas from acceleration or downshift. Giving it gas is strong and responsive and smooth.

Could this be the shim alignment at the tranny mount's geometry not correct? The original Transaxle has more shims.

Or a faulty trans/diff?

I didn't have this with the prior setup and am using the same axles and u-joints. When on the lift, there is no binding.
Also I took it on the Freeway and I have the carbs dialed in really well, at least that's a positive.

A caution about your gear lube selection...

66vairguy wrote:Tue Nov 07, 2017 11:32 am

To correct an error in Bodie's post -- DO NOT USE Redline MT-90 in a Corvair transaxle. Redline's site specifically states that MT-90 is NOT approved for hypoid gears (differential). So it is NOT acceptable for use in a Corvair transaxle since protection for the ring and pinion differential gears is inadequate. Redline does make a modified GL-5 lube that is suppose to work with brass synchronizers called - 75W90 NS GL-5 and states it's approved for transaxles with brass parts. NOTE: Redline NS GL-5 is different vs. their GL-5 which is NOT approved for transaxle use.

For further discussion on this subject, click on the following link...

viewtopic.php?f=55&t=13615&p=94322&hilit=redline#p94322

It sounds like your clutch is slipping whenever engine braking is applied during deceleration or downshifting coupled with deceleration. Based on your description it sounds like the clutch is locking up properly under normal drive or acceleration conditions. I have not encountered this type of problem before, but perhaps the troubleshooting chart below may reveal some possibilities. Is it possible that an error was made during assembly of the clutch mechanism? Could the clutch disc somehow be a mismatch or installed incorrectly (with the wrong side facing the flywheel)?

Left-click the image to enlarge for better viewing...

Left-click the image to enlarge for better viewing...

Thanks Brad, the redline info is new news and I appreciate it. I was using MT-90 for the last year and hope it isn't doing damage. The flywheel side of the disk is to the flywheel. I took it for a drive last night and in a downshift, had a big boom and thought I lost the tranny out the bottom. It stayed running and I limped it home in 1st and 2nd. I guess I gotta pull them apart again. Oh well, live and learn.

Well, I'm getting good at removing the powertrain. It took a weekend, and I was able to remove the clutch and have the flywheel and pressure plate resurfaced. No more shakes or shutters, except in reverse.
I guess this tranny needs some attention. I hope to get away with just using forward gears for a bit, while I get into tranny and diff rebuilding.
Oh boy!

Thanks to Brad for digging up my old post. Yes MT-90 is NOT approved for differentials with hypoid gears (some FWD cars can use MT-90).

On EM cars a shuddering in reverse has sometimes been isolated to worn out powertrain to body rubber mounts.

If you do inspect the transaxle I bet you'll find the pinion shaft (ring and pinion) play is excessive - typical. You can adjust, but new bearings are recommended. The side bearing are very durable IF the lube was kept changed and sadly that is usually not the case. Inside the differential the spyder and sun gears usually are to the point were the hardening is worn. Once the hardening goes these parts wear out fast and can cause a catastrophic failure. Not being negative and you may get lucky and find things are not bad.

Oh - on the manual transmission cars the internal splines of the differential pinion shaft may be worn. Even in well maintained cars the pinion shaft splines are usually badly worn by about 90K miles. Fortunately the corresponding transmission output shaft splines rarely wear. Finding good used pinion shafts is getting more difficult. With a GOOD press you can move the pinion gear to the new shaft - KEEP TRACK OF ANY SPACERS!

Thanks for the info. I did find the Mobil one synthetic 75w90LS which claims to be for hypoid gears. But I do think this reverse gear is missing teeth. I have more trasmissions and need to learn more about how they work anyway. The person that sold this tranny said it looked rebuilt... yet it had a lot of metal in the last draining. I think the wrong or no fluid was used. I may try to bolt up a different tranny to this diff, as it's a 3:27 and kicks ass on the freeway.