'57 Vette Automatic Transmission Leak

[Charles C.]

I have a '57 Vette with the original automatic transmission. The transmission leaks fluid - loosing at least a quart to the ground when it sits for a few days.

I have had the car into a shop that specializes in Vettes and is quite knowledgeable. The transmission was removed and all the mating surfaces were examined for alignment and all seals were replaced. Great attention was give to the problem and several months were devoted to an attempted fix. The transmission was not rebuilt as it was found not to need a full rebuild job.

The leaks persisted and the conclusion that was reported to me was the design of these transmissions is such that when the car sits for a period of time (several days without driving), fluid migrates to an area where it will leak out and that there is apparently not a fix for the leakage.

This sound a bit odd to me (I am not a transmission specialist and can't determine if this could be possible). Is there a transmission guy out there that can tell me if this is possible. Are there any '57 automatic Vettes (or other GM) out there that are allowed to sit for a period of time and not leak out a quart or more of fluid? It just does not seem possible that this would have been a design feature that would have been acceptable even in the 50's.

Thanks.
Charles

[Alexander C.]

Re: '57 Vette Automatic Transmission Leak

I've come across reading something about this before and it was said that the fluid will drain out of the torque converter and overfill the case and leak. I can't remember the source off hand and I haven't installed an original '56 PG back into my car so I don't have any experience yet either, I just came across that in my research.

[John S.]

Re: '57 Vette Automatic Transmission Leak

on the 55-57 powerglides there is no venting in the transmissions. the passenger cars put an anti burbing valve in the cooler lines to prevent leakage. since there are no cooling lines on the corvette some people have drilled a hole on top of the transmission for venting. i have a newly rebuilt transmission and occasionally transfluid will be pushed out of the top of the dipstick when the car is started after sitting for an extended time.

[Bruce B.]

Re: '57 Vette Automatic Transmission Leak

After having my 57 cast iron PG rebuilt and after filling to the proper level I had one incident where it leaked some fluid while parked for a few weeks. Since I have been driving it a lot it does not leak a drop of fluid.
The leakage is usually caused by the torque convertor draining fluid back through the pump and then leaking out through the dipstick tube.
The more you drive it the better.

[Joel A.]

Re: '57 Vette Automatic Transmission Leak

on the 55-57 powerglides there is no venting in the transmissions. the passenger cars put an anti burbing valve in the cooler lines to prevent leakage. since there are no cooling lines on the corvette some people have drilled a hole on top of the transmission for venting. i have a newly rebuilt transmission and occasionally transfluid will be pushed out of the top of the dipstick when the car is started after sitting for an extended time.

Where is it actually leaking from, tho? There are ways to seal the shift shaft, and the TV shaft, so they will not leak. Sealing the TV shaft requires using a Ford part, tho...

No vent is the #1 reason for the leaks. Also, if the trans has been built before, and the small pin that goes into a small orifice in the rear pump was left out, that will cause it to burp on start-up. The '58-up Iron Glides do not have this problem...only the earlier ones.
The front half of the trans is vented thru the dipstick itself, so if the wrong dipstick is installed, it can keep the trans from venting properly. Even with the proper dipstick, the rear(tailhousing) is not vented, so that is the place to drill a hole, and install a vent, if needed.

[Charles C.]

Re: '57 Vette Automatic Transmission Leak

This expert advice is greatly appreciated. It is great to have such experience to tap in to and I know this string is going to help others address this puzzling problem. I will check these points out.

Thanks again. Charles