Tranny guys, TH-400 question

I have a buddy with a TH-400 with a problem. The ****** is a manual valve body, reverse shift pattern behind a blown 454 Chevy.

The problem is the ****** won't move in reverse after it gets hot. You can drive it about 20 minutes and you lose reverse totally. When it's cold it hooks up like it's supposed to.

Any ideas?

Thanks
Root

 

I had a similar problem, I would run for just a short time and would lose all gears, forward and reverse. I figured it was getting too hot, possible turning the ****** fluid to foam because as soon as it cooled down it was fine. I added an external ****** cooler and have never had the problem again.

 

If you do not have a problem in 3rd gear when the ****** is HOT, then the problem is the low/reverse band.

A pressure loss there, bad or hard seal or the trans is too hot.

Does the car have a high stall RPM converter?

 

3000 stall , has external cooler. ****** is 4 years old. 3rd gear is ok.

 

Any chance it's as simple as low fluid?

Some automatics are supposed to have the fluid level checked while in drive from what my trans shop owning friend told me a while back.

He was speaking specifically of my 67 Barracuda trans behind a power pack 273.
Added a quart and it cured the problem of slipping in low.

 

I don't think it's that easy. It would be nice though.

He has checked all the obvious stuff I think, but I'll ask him anyway.

 

If 3rd gear is good....

then it could be a shifter out of whack( adjustment) , low/reverse band servo leak , pin too short , cracked servo piston , blown out gasket , crack in the case at the servo.

so many things

 

So the chances are that we are gonna have to pull the ******. Dang....

 

that's generally the way it is with automatics...if there's fluid it in it, and it slips, out it comes!

 

I'd pull the pan , valve body and rear servo to check for troubles first.

Sometimes the servo piston cracks in the groove area that the sealing O ring sits in.

then pull the ****** out if all is OK in the pan.

 

What would it be if he was loosing third? I have that

 

It's not slipping. It doesn't do anything.

 

"not doing anything" is slipping, real bad.

 

I'm figuring it has to be a pressure issue somewhere.

 

I scanned a pressure schematic of the th400 in reverse, so you can see where to look for problems

 

Cool man THANKS!

 

i'm having a similar problem with the 350 in my truck and it ended up being something wrong with the shifter shaft mushrooming out of place making it leak fluid. i'm not good with transmissions so i let a mechanic i know check it out and that's what he said.