leaking tranny fluid in reverse

[Jester1]

79 3/4 ton 2 wheel drive 454 th400 14 bolt rear.

Wife said she noticted some fluid loss only when she backs up. She is very astute about checking fluids and topping off. She has noticed a fluid loss in checking and always topped off the tranny but she noticed a trail the other day and it was only after reverse.

Has watched a few days and same thing only in reverse. Tranny seams fine operationally, no noises or clunks and shifts the same as ever. I finally have some down time to look it over, but I tend to come up short after the bellhousing.

Hoping it's just a seal or something is loose. It is due for fluid and filter change and may do that this weekend. If you can give me an idea of time for repair on your thoughts that would be awsome also as I need to budget my time on a few things to complete this weekend and her rig can't be down next week.

Jake

 

[Fordum]

I'm sure folks with more experience will chime in, but other than increased pressures and redirect of fluids, there is not a lot of difference between forward and reverse.
I don't know of an internal reason for one to only leak in reverse.

Outside seals do not normally see internal pressures. My best guess, is that its a physical problem. I would check the driveshaft and all engine and transmission mounts.
Odds are something is moving when the torque is applied in the opposite direction and putting physical stress on a shaft seal.
Pop the hood and watch the engine when its shifted from forward to reverse for excessive movement, and carefully get to where you can see the transmission while its shifted.
Hopefully you will see it move a lot causing the output seal to be stressed.

 

[Jester1]

Thanks Fordum. I see a tranny as just being an elaborate pump, so make sense that torque can affect a seal like that. Will have a look at potential movement.

 

[diesel4me]

Dipstick tube might leak worse when backing up,the fluid in the pan will slosh forward as you back up--its not easy to tell where the leak started once it comes out there and oozes all over the tranny case..if it leaks when parked facing downhill its probably the dipstick tube seal leaking..

If its a leak that seem under pressure in reverse,that could be bad news,may be a crack or a porous tranny case where one of the high pressure passages for reverse are casted into the case...there may be a test port thats plugged off on the case too,along with one or two others for forward gears where a gauge can be hooked up to check internal pressures,maybe its leaking there??...

 

[Greg Ducato]

Check the vent tube as the possible leak source, fluid pressure in reverse is almost three times higher than forward. A cross leak at the pump gasket can push fluid out the vent in reverse.

 

[Jester1]

Thanks for the input guys. Wouldn't you know I have time to get stuff done and the weather goes bad. I will check those locations as soon as the driveway dries out.