Do I need to worry about putting a specific modulator in a th400 that is behind a boosted engine? Perhaps one from the 80 formula would work since it had a factory turbo?
or does it matter?

 

Imo you should get a manual v/b but if you want the trans to shift automaticaly get an adjustable modulator.

 

TCI sells a valve that goes in your vac line to block boost, has to be mounted a certain way to work-i had one on a man shift 4L80E where they used the mod in place of the force motor
i have run them just the reg way ok, but always felt it shifted better under power as a man v/b

 

I already have the trans put together and installed so I dont wanna pull it for a manual vb swap. this is a cruiser as much as it is a quarter mile monster.
I will probably just run it the way it is and see how it reacts. if I start spewing tranny fluid out the seals I will know why lol.
Does anyone know by chance how the modulators on a TTA from 1980 was setup from the factory? maybe they had an inline piece I could get my hands on if required. if not ill go the TCI route forcd ind mentioned.
thanks

 

There are a couple of things you need to do for the TH400 with boost.

You can run the automatic VB no problem, we've done so on TH400s in turbo applications to ~900 HP so far without issue (years on that trans).

The boost checkvalve already mentioned is a TransGo piece.

There is another important modification to do but I won't discuss it on an open forum. PM me for details.

 

Jake,
this is old ^^, but i need help with this same issue. We've already used the checkvalve, need to know the other mod to get the auto/manual th400 to shift and last.