trans leaking

[tynall44]

took my fmx that was in a 73 now in my 69 they say its building up pressure and leaking out of the vent ,,, what causes this and how do i fix it

[fordman]

to much fuild is one reason. but i would say its due to high pressure somewhere. bu ti have no idea where or how. maybe a fluid and filter change. and see whats in the pan when you take it off. that may tell you something.

[Jake11]

Look and make sure where its leaking. It could be something else.
Two reasons it can come out the vent. It's overfilled, or it's overheating.

[flyboy2610]

It's possible you have a restriction in the tranny lines, causing a backup of fluid and increased pressure. I would pull the tranny lines off and make sure they are not plugged, and also make sure that the cooler in the radiator isn't plugged. If it all checks out, install an aftermarket cooler and make sure the tranny isn't overfilled. If it still does it, and it smells like it's overheating, you may have a pump going bad and it isn't circulating the fluid fast enough to cool it. Time to pull it and rebuild it.
Tranny fluid expands when it heats up, and I have a hunch that's why you're getting it out the vent.