Car is my fiance's family rustbucket (I mean heirloom) 1965 Mustang, with an unknown year 302 and C4 trans.

Short question is: What is the correct way to refill a C4 transmission with fluid? I tried the usual way of down the dipstick and the fluid immediately comes out of a hard line noted below. I've been googling all over to try and find out what that line is, and if it is missing a stop or something, but all of the exploded pics I get do not label it. Is there a different procedure to refilling the trans? Through another case opening maybe? Forgive the ignorance, I don't know a damn thing about these cars.



I noticed it was out of fluid when I tried to take it out for a quick 'round the block spin, because it was hardly ever driven before I got here. I'd like to get it refilled so I can try and figure out where the leak is coming from and how bad it is. (Seems the most likely area from some the sites I've been reading is a funky ring gasket near the gear selector)

 

Fill it through the dipstick tube idling in park. Read the dipstick. The pic is of the vent. Sounds like its overfull or not running when being checked.

 

Good to hear that's just a dump vent. The car was not running when I tried to fill the case. I stopped after less than a 1/2 quart was added when I heard it running onto the garage floor.

However, the dipstick did read super low when it was running and warm though. I noticed as I tried to move the car off of our driveway and it kept jumping in and out of gear. I'll check it again tomorrow.

 

As joe stated check with engine running, and warm. If it isnt too full the must be a pressure leak (internal) that is pushing the fluid out the vent