I have a 65 corvette 365 hp 4 speed (M21). Tranny was rebuilt and replaced clutch and pressure plate (Centerforce dual friction) 5 months ago. Was 17 years since last rebuild of tranny and clutch and PP replacement. The problems started about 4 weeks ago (car's in the shop for 3 weeks now).

Trouble is:

Problem 1. After driving for a little while and is at temperature, at a complete stop (engine idling) when shifting from 4th back to 1st, it will not go back into 1st gear. It will NOT go back into any foward gear without a lot of difficulty. It does not grind, it just will not go into gear.

Problem 2. Also, if you try to shift into reverse, it WILL grind reverse gear every time.

Problem 3. Once in reverse, it is difficult to pull it out of reverse.

Troubleshooting done:

We looked at the clutch and pressure plate while engine was running. With clutch engaged, the disk moves very very slowly slightly counterclockwise. It is supposed to stand still.

We removed the tranny and have looked at the clutch and pressure plate. They show no apparant problems. PP fingers all the same. Clutch has no apparant warp.

We looked at the surface of the flywheel and is clean

We have checked if the crank shaft has any forward play, and that is not a problem (< 1/1000th).

We adjusted the clutch linkage out significantly more. This had no affect on the problem.

We checked the shifter linkage for proper by pass and movment and all is normal.

The transmission is now being disassembled to see if the problem lies within.

Question: If it is the transmission, what could be causing these problems? Any other ideas?

My bet would be the clutch, either it's toast, or you are not getting the required travel to fully disengage it.

Vince

Sounds like a clutch problem. Also check the shifter linkage. The old Muncie shifters in the Corvettes get pretty sloppy and easily get out of whack

Sounds like the clutch is not fully disengaging. Or maybe the disc is warped.

If you can shift the transmission easily with the engine off. The problem is not internal to the transmission. If the transmission is hard to shift while the engine is off the problem is internal to the transmission.

I noticed you said that the problems occur AFTER the engine warms up. I think that would exclude the linkage. And, I can't think of anything inside the trans that would be heat sensitive. I'd also have to vote for the clutch.

Let us know.

AMS3, check the pilot bushing to input shaft clearance. When I put the 350 in my Willys, I had the same problem. The answer was that the input shaft was "Sticking" to the inside of the pilot bushing after it warmed up.

good luck...

CJ

You might want to look at both the input shaft and the splined section on the clutch itself. Possibly the problem is a burr or just a tight fit causing the clutch to hang up on the input shaft.
I had that happen and it sounds like the symptoms are the same. An easy cure is to find a small single cut file and clean up the splines a bit until they will slide smoothly without much effort.
A light massaging with a file will not harm anything but will certainly help to free things up a bit. Also a small amount of graphite powder which you can obtain from a locksmith type shop might help.
Also be sure to take a good look at the brass pilot bushing as they are soft and really easy to mushroom.
Good luck with that and let us know what you find.

Just for info the dual friction requires .360-.400 of throwout movement for full dissingage. I think the GM check for dissengage is to put foot full on clutch with the trans in neutral and wait 9 seconds and there should be no grind.

I guess I'm a little late on this subject, but when you pull that tranny out of your vette, be sure to use a dummy spline to align the cluth and pressure plate before you put the trans back.

This thread is over two years old. Just a guess the tranny is back in.