Transmission Cooling Line Question
 

On my TH 400 Tranny there 2 lines coming out and were connected originally to the radiator. On the radiator are 2 ports for the tranny line. One is the upper and the other the lower. Which one is the incoming and which one is the return?

Second question is a transmission cooling routing question. Does the tranny fluid travel to the tranny cooler mounted up front first, then through the radiator tranny cooler and back to the tranny or to the radiator tranny cooler through the tranny cooler mounted up front and then returned to the tranny?

Mitch,
I can't help on which line goes where on the TH400, but my opinion would be that it should flow from the trans to the radiator and then into the tranny cooler and then back to the tranny.

Doing it this way, it allows the fluid coming out of a radiator which has coolant that normally runs at 180-210 degrees to further cool the fluid as it passes through the tranny cooler before returning to the tranny.

the lower one:D is out

Thanks George, looks like the guy who had the truck before me had it the same way, going to the radiator cooler, then to the aux. cooler, and back to the tranny.

Thanks Mark for the location of the radiator output.

On the trans, the upper fitting is return, lower fitting is out to cooler. On the radiator, the lower fitting is in from tranny, upper is out to tranny.

From all my research, it seems it's best to route this way for best cooling.

Come from tranny to aftermarket cooler, out to lower fitting on radiator, out of top fitting on radiator back to tranny.

Reason is if you go to radiator first and then to cooler, back to tranny, it will cool the fluid too much. If you go to the cooler before the radiator, it lets it warm up just a tad first.

This is the way I have mine routed and believe me, it works very well. I have a trans temp gauge so I know for sure it does and not just hearsay.

Thanks for the input Mike! Where is your temp gauge located for tranny temperature?

You have to braze a brass fitting in the pan for the temp sender.

Now I remember...You even had to have reworked it because of a leak, right?