Trans Leak after replacing coolant lines @ flanged head into housing?

Question

I replaced the coolant lines on a th400 trans. First I used pipe thread tape on end that go into trans housing. No leaks. Great! But when I start engine the trans fluid leaks out from the pipe that goes thru the connectors that screw into trans housing.

What did I forget to do?

Answer 1

Loosen up the retaining nut a couple turns then fiddle around with the line to get the flared end to feel seated and tighten the nut slowly while wiggling the line slightly making sure it's mated to the seat.You don't need teflon tape,the seal is made at the flare and it's seat.

Answer 2

Been there done that on a 1976 Suburban with a 454CID/TH400. The brass "plumbing" pieces that screw into the tranny and then you screw the lines into will strip very easily when you cross thread the lines in. You will not even notice until it's too late. You can replace the brass piece, it will unscrew from the tranny, and try again but don't assume that your eye is correct in telling you that it is "straight" on lined up perfectly when you start to turn the line connectors.

You can use a pair of pliers or an open end wrench to slightly bend the lines just before the end where the connectors are so that the lines will "fall in" to the brass couplings perfectly and there is little chance you will be twisting your way toward another cross threading. If it is lined up perfectly, you will be able to twist the connectors into the brass fittings with your fingers. Just put a drop of tranny fluid on the threads and twist with your fingers and finish with the wrench. This is a low pressure connection so you don't have to be torqued too tight.

I picked up the brass piece from a local tranny shop but you can find them at the dealerships or auto parts stores or if that doesn't work, LMC Truck. (LMCtruck.com)

The onlyother thing to check is that the new line connections are "deep enough" to bottom out the lines against the brass plumbing connections. There is a certain depth to the threaded coonection on the steel lines. You'll have to compare this with the old lines. For example, you can't use a brake line for a tranny line as the actual connection isn't deep enough or long enough to seal the flared end to the brass fitting or bottom.


Good Luck!

Answer 3

Depends on the fittings on the transmission-is it the same that came out, or is it a rebuilt? They sometimes had to have adapters for the variuos cooler line styles used.

Answer 4

cracked flare on the line