blue 67 coupe

So the good news is I figured out my transmission pan was leaking because the old one was warped. So I got a new chrome one today and no more leaks from the pan. Well I was getting excited because it was holding the fluid and was about ready for a test drive but all of a sudden a huge leak but not from the pan. It was around the neutral safety swith it came from like a quarter inch hole and i'm not sure if its suppose to run to something else or is it supposed to be plugged.
I put a red box on the picture from where the leak was. There was a bunch of build up and stuff so I pulled it out and found the hole.

I tried to zoom in on the hole but my camera wasn't good so I made a white circle and its basically just a metal tube and it was just draining the fluid.


I don't really know what it is so i'm hoping someone could tell me what that is and if its suppose to be plugged or if its suppose to run to something else.
Thanks

blue66mustang

That is the vent tube on the trans. The fluid will leak out of there if the trans is overfilled or the torque converter drains back into the trans housing. There is a check valve in the pump that is supposed to stop drainback. It may be stuck.

blue 67 coupe

Does that mean I will have to take the transmission apart again? How exactly would I check to see if the valve is stuck?

blue66mustang

Unfortunately yes you will. The check ball and spring are located within the oil pump housing. At the minimum you will need to remove the transmission , torque converter and pump. You’ll then need to open the pump up to get to the check ball and spring. There may be dirt in the orifice or the ball may be worn. This will require careful disassembly and reassembly. Something I wouldn’t recommend in your garage as the pump clearances and cleanliness are critical.

Your absolutely positive that the fluid is leaking from this tube. It can also leak from the gear selector shaft. I’m not doubting you but the two repairs are night and day in complexity. Try and see if you can slip a piece of rubber tubing over the metal vent tube and let that hang down below the level of the pan by one inch. This will positively confirm leakage from the vent.

Keep us posted..

2+2GT

The selector seal is cheap and easy compared to the above description.

groho

The C4 is known for leaking out the vent tube, it's called drain-back. The converter drains back into the tranny body when the car is parked. Sometimes it happen same day, others it takes a week before you see the leak. I've got a fresh build on my tranny, and it's does it also if it's parked for a week. You can spend the time and money to correct the pump check valve, or bend a new vent tube (5/16" tubing). I made a longer tube that points up at a 45 and then down past the linkage so I can actually see if it's leaking. When it does drain back, it stays in the tranny and not out the vent tube.

blue 67 coupe

Alright well the car is fixed now and back on the road. Thanks to everyone that helped with the problems I appreciate it.

Piraya33

What ended up being the problem?

blue 67 coupe

At first the bolt in the trans was loose so i tightened that and it shifts again. Then it leaked replaced the gasket and trans pan and sealed it with copper silicone. Then we poured too much trans fluid and hadnt started it so once we started it the fluid cycled through then we added the rest.

But it got fixed just in time was even able to make it to the local Mcdonald's car show and took 2nd in its class. First place was a 65 fastback but the owner is my friend's dad and the car is restored from the ground up so it was well deserved. Some of my friends were saying I might have a chance because they saw a ton of people voting for me but if they would have gave me first I would have given it to the 65 because his was absolutely stunning.

MayorDaly

Groho, It looks like I have that drain back issue on my 66 C4, Is there any
thing to flush through and clean the valve i.e... slick shift or cleaner?
Can't afford to tear it down for a while, If I extend a 5/16 tube up enough,and maybe even an overflow canister (as some radiators have)
will it drain back into pan and then pump when car is driven?