M-21 Stange Problem

**ANDY M** · #1 07-25-2004, 09:32 PM

My car has an M-21 that came out of a '67 Vette. This problem just started after having the motor rebuilt. If I'm driving at city speeds it's quiet and shifts normally. If I hit the gas and open the secondaries, it locks up in that gear (ie it won't shift from first to second, or second to third). I have to come to a stop, bang it into neutral or third, then muscle it out of gear before it will work again.
Any ideas?
Thanks,
Andy

Pantera · #2 07-25-2004, 09:41 PM

First check to see if the tranny mount is good. It may be colapsing and coming in contact with the cross member.

If you have a stock shifter that hooks to the steering colum to provide a steering colunm lock then take the rod to it off at the shifter and see if that is the cause.

check the obvious and be sure the shifter is bolted tight to the tranny. If it is on a plate but not actually bolted to the rear of the tranny then that could be your problem.

Tell us more about what car you are having the problem in?

The problem may not be inside the tranny. For your sake I sure hope it isn't.

Pantera

Seattle Sam · #3 07-25-2004, 09:49 PM

Your shifter may be binding due to twisting or rotation of the trans. I would first check for a broken motor mount or trans mount. While you're there check all your bolts holding the mounts on and together. Finally make sure your bell housing is bolted tight to both the engine block and the trans.

Maybe the problem is in the clutch not releasing properly after you hit it with a dose of torque - check the throw-out bearing, fork, etc.
-Sam

**ANDY M** · #4 07-26-2004, 04:02 AM

This is the tranny on my COPO. The engine is a CE stamped 512, everything is stock, except the block is now bored .0100 over. The motor was totaly rebuilt. Everthing but the crank and 5 of the piston rods is fresh, including a new flywheel, clutch, and the rest of the clutch assembly.
I will have the mounts checked, since I don't recall paying for new ones, but I have been trying to keep it under 4500 rpm while breaking it in. Only about 300 miles since the rebuild.
Andy

**firstgenaddict** · #5 07-26-2004, 05:10 PM

Did you check to see if the bellhousing flanges are still "Square" on the block and trans? If not the trans will not line up correctly. Also there have been cases of dowel pins not being in the correct position.

NCGuy68 · #6 07-27-2004, 05:05 AM

[ QUOTE ]
My car has an M-21 that came out of a '67 Vette. This problem just started after having the motor rebuilt.

[/ QUOTE ]

Simply rebuilding the motor didn't cause the tranny to go bad. You have other issues.

Follow the advice mentioned above on this thread.

**ANDY M** · #7 07-27-2004, 06:26 AM

Thanks for the advice, guys. I beleive now that the problem is with the mounts at the back of the trans.
The bellhousing was squared up with the trans, but the torq issue is one I had not considered. Hopefully I can get it up on a hoist to have it checked out.
Andy

SMGCO · #8 07-28-2004, 07:58 PM

Andy check to see that your shifter is properly adjusted. There is an alignment/sight hole at the base of the shifter that needs to be able to pass a 1/4" drill bit ( or similar size object ) through. You can go to the Hurst ( Mr. Gasket ) web site, or call them, for more details.
Also, check that your bellhouse is properly aligned to the block.

Dedicated to the Promotion and Preservation of American Muscle Cars, Dealer built Supercars and COPO cars.