Here’s why that Powerglide expels fluid

April 1, 2009 | By Richard Prince

Question:

This letter is in response to your reply to Russ Alberg in the February issue concerning the Powerglide transmission in his 1956 Chevy. (After being parked for a while, the transmission expels fluid up through the filler tube.)

I am recently retired after 33 years as a transmission rebuilder. The past 16 years were spent working as a rebuilder of classic units for one of the best-known suppliers of antique automatic transmission parts in the world. The question asked by Mr. Alberg is one of the most frequently asked questions I received in my position so I would like to take this opportunity to steer him in the most likely direction to solve his problem.

First off, a cast iron Powerglide does not have a “pan.” The case is fully enclosed and as such is unique in American automotive design. Rebuilders refer to his issue as “drain-back.” The cast iron Powerglide is designed to prevent this through the use of a metal sealing ring which fits around the input shaft and seals oil from draining from the torque converter back into the main transmission case. The ring seals against the inside of the stator support which is integral with the valve body. In this unit, the valve body is affixed to the rear inner side of the bell housing and again is unique to American design.

The very common problem with this unit is that over time and use, the sealing ring wears into the inner surface of the stator support to the point that it can no longer retain the torque converter oil over an extended time, causing it to gradually leak down. When the engine is eventually started, all that excessive oil in the main case has nowhere to go so it blows out the filler pipe until a manageable level is reached.

Of course, this leaves the transmission dangerously low on oil and the missing oil must be replaced before driving to avoid further damage.

This condition will vary in intensity depending upon the actual degree of wear of the ring into the stator support.

The fix for the problem is to remove the transmission and disassemble the bell housing from the unit and replace the valve body assembly, the sealing ring and sometimes the input shaft as well if the ring groove is worn enough to cause side-to-side motion. Rebuilt valve bodies are available from sources specializing in antique transmission parts. One such source is FATSCO Transmission Parts in Pine Brook, New Jersey. Their contact number is . They can supply all the necessary parts, seals and gaskets to complete this job.

A special note to Mr. Alberg; do not attempt to do this yourself as removing the bell housing incorrectly can result in severe damage and unnecessary expense. Either have a mechanic experienced with this unit do the repair or purchase a repair manual and follow it to the letter.