C2 66 L72 Leaky M21 Transmission

[joe gushen]

I recently rebuilt my 66 427 roadster and had my M21 rebuilt before I installed it. Unfortunately, the guy that rebuilt it has passed away.

My problem is that I'm getting a leak from the front of the transmission at the input shaft. I do have the car slightly modified in that the car does have a rake. The back of the car is higher than stock and the front of the car is slightly lower than stock.

I'm not a transmission guy buy from what I understand, there is no seal in the front of the transmission and the housing has no cracks. I had one old Hot Rod guy tell me I should epoxy that front bearing in! Sounds like a little extreme to me.

Any help would be appreciated. Thanks to everyones help in the past. The car is done and I was able to put 400 test miles on it. What a blast!!!!

Thanks

Joe Gushen

[Joe L.]

Re: C2 66 L72 Leaky M21 Transmission

Joe-----

I don't think that the rake is the cause of the problem.

You have been told correctly that there is no front seal on a Muncie transmission. However, there are 3 VERY common leak sources on the front of a Muncie. These are as follows:

1) The bearing retainer bolt holes become worn and fluid leaks past the threads. If you're sure that the oil is coming from the retainer area, this is most likely the cause of the leak. The fix is installing Heli-coils in the holes (with Lock-Tite GREEN to seal and lock the inserts) and then using a non hardening sealer such as silicone RTV on the bolts. Sometimes, you may be able to get by with just the RTV on the existing threads;

2) The hole in the main case for the countershaft becomes distorted due to long use and/or repeated removal of the shaft for rebuilds. The best way to repair this problem is to have the case professionally bushed. However, you can often get by with the application of silicone RTV, applied to the external interface between the shaft and the case. However, you ABSOLUTELY MUST have the area 100% oil and grease free prior to doing this or you won't get a seal.

3) The oil return hole in the front of the case (under the retainer) is plugged. This often occurs because someone uses too much silicone sealer on the gasket and it "oozes over" and plugs the hole.

By the way, I don't see how applying epoxy to the front bearing would do anything. Under any circumstances, the bearing is going to pass transmission fluid. The fluid is designed to be returned to the case via the oil return hole in the front of the case and the corresponding pathway machined into the inner side of the bearing retainer. Epoxying the bearing would create problems but not solve any.

[Keith G.]

Re: C2 66 L72 Leaky M21 Transmission

I have the same problem on my 67, we replaced the motor and seen it was leaking next to the input shaft, there is a rod that runs though the trans, and is exposed at the front, we siliconed around it but have not put the motor back in yet, talked to an old muscle car mechanic who said the aluminum case likes to twist, unlike the cast ones.