TH400 slip

[Smaart Aas Saabr]

Had a couple of "huh?" slipping issues with a TH400 yesterday... first slowed down hard to turn onto another street and then vrooom rpm flare / major slipping. stopped and checked oil level seemed marginally low, I put some ATF-oil inside and the vehicle moved fine.

Then a few miles later, just after a stop sign, maybe 10 feet of acceleration then slipping. Of course this puts me right in the middle of the intersection, the worst possible place

Eventually it gets going again and then it worked fine for the next 1/2 mile until I parked.

Now a couple of years ago using the same vehicle on cold winter days (around say 10 to 40 *F) I had no drive whatsoever especially in reverse. The engine would need to idle for 3-4 minutes and then the truck ran fine for hundreds of miles. I attributed this to cold worn seals that got hard and wouldn't hold line pressure? I think Reverse requires an even higher pressure so that held my theory.

Friggin automatic transmissions

Anyway so what is going on, likely tranny rebuild necessary or is this something I might be able to change fluid and be running again? I don't want to change the fluid in a "stick fingers in some dyke and pray" manner like some would because that would likely put me in a VERY expensive situation with a loaded trailer on the side of a highway 500 miles from home...

[Johnny P]

Sounds like a overhaul is likely needed. But first I'd drop the pan and check to make sure the filter isn't loose. You might also be sure that the modulator isn't full of oil.

If you overhaul it pay special attention to the pump clearances and regulator valve.