The Stovebolt Site Forums The Shop Area Engine Shop Powerglide transmission leak

From:Trucktinker
Replaced rear seal. Filled to proper level. No leaks for several days, then about two quarts on floor. Someone told me that if driven once a week, this won't happen. Why won't it leak if driven once a week? So I have experimented for a few weeks and found, bringing the level up to one quart low and running a few minutes (back and forth from "L" to "R" a few times) and let set with pans under rear and shift linkage, only a few drops in each pan after about three or four days. The dipstick will show just a tad at the end with the engine off and will build just a bit each day. More drops seem to start where the shifter rod goes in than anywhere else? Could this happen because it takes several days for the torque converter to leak down into the sump in the transmission and build-up to the shifter rod, hence the only leak is comming from that seal? The only reason I have'nt put in the last quart is so it won't leak back out and have to be strained to be put back in. I could be way off base on this, but it is the only thing that seem to make sense. The plug is out of the bell housing and no leak there? Anyone else have any ideas?
Truck Tinker

Sometimes seals need to swell a little bit to seal properly.
This happens from use. Also after driving for a while it's a good idea to retorque any bolts that were removed when replacing the seal.

It sounds like you have a 1955 or later transmission, correct? It doesn't matter, really; the torque converter should drain pretty quickly after shutting off the engine, which means the fluid level should rise above the normal full mark (running, hot level). I don't remember specifically, but I'm sure there is a seal on the shifter shaft, although I think it is only accessible from inside the case. There is another shaft for the throttle valve, which has the throttle rod that attaches to the carburetor. That shaft also has a seal, I'm sure, but again I don't remember specifically. The throttle valve is inside a squarish cover at the base of the torque converter housing. There should be a shaft extending from the cover; the shaft should have a lever attached, which in turn holds the throttle rod that attaches to the carburetor. That whole mechanism gives the kick-down (passing gear) when you go to wide-open throttle.

Another possibility for the rear seal leakage is a groove on the seal surface of the U-joint yoke. Did you check that?

Don't know if this answers your question, but maybe it will help.

Harvester

It may even be the o-ring on the filler tube.

This is a common powerglide problem. It's true that if it is driven often it is less likely to occur. Some guys jack up the rear when it is parked for a while. The cast iron PG's have what is called the "burp" which is caused by a failure in the one-way valve in the pump assy. Danchuk and Classic Chevy Int sell a one-way valve that is installed in one of the trans cooler lines which can help.
Fred