I had my th350 built with roller clutch (sprag) and hardened race. It lasted about 8k miles. Any recommendations on a sprag that wont break?

Will these specs hold up behind a 455 with 425HP 520+ torque?

TCI#890-327900
Drum & Sprag Kit
TH350
Iron Direct Drum
36-Element Sprag


5 clutch direct piston (piston machined for 1 additional clutch)

Sun gear bushings doubled up and lube holes drilled, de-burred.

NEW intermediate roller clutch (sprag) and hardened race. Race inside diameter specially prepped.

Direct clutches MUST be dual fed. This can be accomplished internally or by using a TransGo Kit. I do it both ways depending on application.

Valve body modifications to firm up shifts. Nothing fancy needed, and not too fimr on the 1-2 shift.

Heavier pressure regulator spring for increased pressure.

Governor modified for higher rpm shifting.

Pump machined for better sealing and pressure.

700-R4 low/reverse roller clutch and support.

Endplay setup on the tight end of spec,

Borg Warner or Alto Red plates.

Snap rings tach welded for high rpm applications.

 

I don't have the expertise to answer your question -- which is why if it was me I'd let the transmission shop doing the work choose the components. I don't see how anyone would be willing to warranty the finished product if you make the recipe. If you're doing the build yourself, then I'd suggest you're in over your head, otherwise you wouldn't have had to ask the question.

One thing's for sure: for a high horsepower application -- especially a TH350 behind a stout 455, I'd buy the parts from Coan long before TCI.

 

I would just go with a th400 and a 34 element. You are paying a lot for parts and a 400 will handle that power easy. JMO

 

Thanks for your opinions.

The warranty work is free. I am just providing the 36 element sprag. He said that all the other items I listed have been done already.

With the exception of
Governor modified for higher rpm shifting.
700-R4 low/reverse roller clutch and support.


That being said if I want to upgrade to a fresh built strong th400 I would need to come up with 1500. Which I don't have.

 

I can tell you from personal experiance, the cheap aftermarket sprag races are weaker than factory! For your performance level, a stock race should live fine. A quality race from Coan, TCI, or HUghes would be a nice upgrade. I have built countless TH350s with stock componants (including races) that live deep into the 11s. Make sure you keep the wave plate in the intermediate clutch, and keep the accumulator spring in the accumulator. You can eleiminate the spring in the accumulator in the valve body, thats for 3rd gear. There is no sprag to break, it can shift hard enough to knock the dash out of the car without concern.