Any recomendations on heavy duty parts to replace when rebuilding a th 350?I already have the trans go shift kit and a basic overhaul kit.I want to make this thing as bullet proof as possible.
thanks in advance

 

you want durable? build the trans, and then instead of trans fluid, fill it with cement. guarantee it'll never wear out

 

you know... i never did like you!

 

Wider bushings, hardened roller clutch race or sprag type drum, machined direct piston for 5 frictions.
Keep the vacuum modulator.
increase fluid flow to the converter (drill the proper passage.
Loctite and stake the pump bushing in place.
Inspect all parts.

 

The weakest part is the intermediate sprag. It locks the drum when you shift from first to second. I blew up one last year. When it goes it'll usually take out a few other parts with it. To upgrade the sprag you need to buy an aftermarket muti-element sprag (34 element I think) plus the drum that it fits on and the sprag race. These parts aren't cheap but it costs money to try and bulletproof a TH350.

Buy the book "Turbo Hydra-matic 350 Handbook" from HPBooks. Everything you need to know is in there including all the other modifications needed.

The shift kit does nothing to beef up the tranny except that it reduces the wear on the clutches by engaging them quicker so that they don't slip as much. The basic overhaul kit won't have any performance parts either. Stock replacement clutch plates, thrust bushings etc will work but performance ones are recommended.

It's easier and cheaper to just build a TH400. Even a junk yard tranny that just has a shift kit thrown into it will take more abuse than a TH350 will.

I swapped out the 700R4 for a TH350 a couple of years ago. I only blew up the one TH350 in 2 years. This winter a built up TH400 goes into the car because I know the TH350 won't survive next years race season.

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87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block

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87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

[This message has been edited by Stephen 87 IROC (edited November 28, 2001).]

 

Replace ALL bushings and as mentioned, use the wide bushing on the direct drum. Set endplays down to .001"-.010". Use the plasitc bushing inside the output shaft. With the TransGo unless you are really making power, four direct frictions will be fine but you can go to five. There should be Five Forward and Low/Rev Frictions and three Intermediate. A hardened race is a good idea but the stock one will hold up better than you think with the TransGo kit. Make sure the pump gear top clearance is MAX .001". If you have no EGR or use low gears, use the small red stripe modulator. Otherwise get the larger black stripe one. Use all Borg Warner Frictions.

 

Don't forget to do that same modification to that 400--that is replace the whole direct drum with one that has a sprag type clutch.
A friend of mine just blew up two of the stock roller clutches (they look just like the ones in the 350) in his 400. Just as expensive if you ask me, a common misconception on the turbo 400.

 

Thanks for all the info guys!! One more question for you.a guy on ebay is selling rebuilt th 350's ( i am not buying one from him;I was just browsing) and saw this in the listing "700r4 low reverse sprag installed"
anyone know if this is a good idea or not?

 

It's easier to upgrade the 400's drum and sprag. You buy the B&M 34 element sprag and find a late 60's TH400 drum. The TH350 never came with the better sprag and drum so you need to buy all those parts new from the aftermarket.

I paid $8 for the late 60's drum from the junkyard.

 

It's fine to do but you have to change the center support to do it since the Low Roller (it doesn't have a sprag) is wider.

 

Lucky you. This friend of mine sold that 400 that broke two roller clutches, the guy who bought it paid a shop $800 to put a 4L80E 34 element sprag and drum in it.

I later took it apart after that shop went out of business, the trans had no third gear, it was just a sealing ring out of place. The new sprag looked strong, I'd trust it to take some abuse.