Use caution when installing this kit
This letter is in response to your February reply to Russ Alberg concerning the tendency of his 1956 Powerglide transmission to leak oil after the car sat for a while. There is a check valve in the front pump of the Powerglide transmission and this valve is supposed to keep fluid returning from the torque converter from reaching the main case. This prevents the case from overfilling and leaking. The failure of this check valve is one cause of fluid leaking when the car sits. You will have to pull the transmission in order to change this check valve, or you can repair the valve using a special kit.
The kit that Mr. Harris is referring to is sold by Classic Chevy International (classicchevy.com) under part #19-28 and retails for $19.95.
The kit consists of a check valve and two compression fitting assemblies. By installing the check valve in the line that carries transmission fluid back from the radiator to the transmission you do the same thing that the check valve in the pump is supposed to do, namely prevent the fluid in the torque converter from flowing back into the transmission’s main case.
If you choose to install this kit, make absolutely sure that the arrow on the check valve is pointing toward the transmission and away from the radiator
when you install it. If you install the valve incorrectly it will prevent fluid from getting back to the transmission, causing quite a bit of damage.