Following up on this issue.  I was able to move the the transmission back far enough to see the end of the shaft.  When I unbolted the transmission from the bell housing, gear oil poured out of the cavity between them.  Obviously, this is where my leak was located.  Looking in, I saw where the shaft hole had space for a freeze plug.  This freeze plug was missing.  We made a plug and JB welded it so it wouldn't come out again.  Problem solved.

When I had the transmission out last summer for an engine rebuild, I installed new seals on the O/D solenoid and the shift arms.  My leak is coming from the front of the transmission.  I'm pretty sure the leak is coming from the shaft hole in the front of the case. As soon as I have a chance, I'm going to pull the transmission back and see if I can seal the hole.

Sent a PM


64F100 57FAIRLANE500

The T85 Overdrive tranny in my ’55 (originally out of a ’63 Galaxie) leaked gear oil from the electric solenoid area.  Wasn't a lot of oil but enough to always leave a spot on the floor.  I ended up putting a second seal on top of the first seal in the case where the solenoid installs and that fixed that particular leak.

Lorena, Texas (South of Waco)

This is a possibility.  I have always thought the leak was coming from the input shaft.  The older T86 transmissions don't use a seal, they have spiral groves to direct the oil back in.  I have determined this is not the problem as the clutch, pressure plate and inside of the bell housing are all dry.  There are only a few more possibilities.  It could be leaking from the front of the case where the shaft hole is drilled.   If that is the case, you would think you could see it?  Perhaps the gear oil is working it's way out the side or around the case?  If it continues to leak, I am going to attempt to pull the transmission back and seal the shaft hole with a gasket or sealer.  I can't check the vent unless I pull the motor and transmission.   That may be necessary. 

I now know the best way to make sure the transmission and O/D unit are totally full.  Removing both plugs and filling them from the O/D unit works best.

It sounds like your trans was running with excess oil. Adding oil to the O/D unit until it runs out the trans fill plug is correct. I have never owned or worked on a T86 trans but isn't the vent a small hole in a raised section of the tin top cover? The hole in the gasket looks like it may be off-set enough to not allow oil to get to the vent hole. Maybe excess oil could have been thrown at the cover gasket and possibly made it's way to the vent hole. I'll try to include a couple pics of the T86 from my 64 truck manual with the vent hole circled. I totally share your anguish solving this leak. Hope this helps, JEFF.............


64F100 57FAIRLANE500

I'm still chasing a leak in my 1955 TBird with a BW T86 O/D transmission with a R10 overdrive.  I thought it might be at the cluster shaft hole in the front of the transmission.  It is difficult to tell if the leak is engine oil or transmission fluid as they both look similar.  Today, I jacked up the car in the my garage.  I started the engine, warmed it up and went through the gears to get everything moving.  Everything works perfectly.

I crawled under the car and removed the bottom dust cover on the bell housing.   The clutch and pressure plate are bone dry.  The rear engine seal is not leaking.  The transmission input shaft is not leaking. My engine has a road draft tube.  I can see fumes coming out of the tube with the engine running.  No smoke.  No oil. Just fumes.

I removed the top transmission lube fill plugs on both the front of the transmission and the O/D unit.  Gear oil came out of the front hole. Nothing came out of the rear hole in the O/D.  I let the gear oil drain until it stopped.  A few ounces came out.  This lead me to believe I may be overfilling the transmission.  I tried to add gear oil to the O/D unit.  To my surprise it took some.  I was not aware that the transmission and the O/D unit are joined.  I continued to fill the O/D unit.  Gear oil started coming out of the front oil fill hole again.  I concluded the transmission is totally full.   I let both holes drain and reinstalled the plugs.

I have no idea where this gear oil is coming from.  It seems to be coming from the passenger side of the transmission.  There is nothing there that could leak except the fill plugs.   The mystery continues.  We will see what happens.

It's worth a try.  I never thought about the transmission leaking from that spot.  I always assumed it was leaking around the input shaft. I couldn't figure out why the clutch and flywheel stayed dry.  Makes sense.  Thanks!

Maybe you can slide the trans  back far enough to clean the area of the cluster gear shaft area with brake clean and dab some RTV on the area and slide the trans back in place.

John - "The Hoosier Hurricane"

Thanks for the info.  As you know, removing an O/D transmission from an early TBird is a daunting task. This requires either removing the engine or loosening the bell housing as the transmission will not move back far enough for the input shaft to clear the bell housing.  For now, I'll just have to put up with it.