Think about this before you look for HP

[JB55]

I think the 3rd gear clutches cant take the revs - it shifts at 6500

Absolutlet not! A well built 400 can handle a ton of power and rpm. I shifted my old 406 at 7400 and the trans held up with no problems.

 

[pontiacgp]

I got the turbo 400 through Summit. It looked "brand new" to me even though GM hasn't made one in a decade or two.

did you check with Summit about a warranty?

 

[MightyCarlo86]

Could that be an issue with the governer or throttle valve pressure? Not familiar with those transmissions.

 

[84GP455]

The TH400 is very strong I had one in my car for the last 25 plus years and I also went through 3 rear ends with it. It was a 71' and the code said it was either out of a diesel school bus or a motor home. I just swapped it to a TH2004r last summer which seems to be holding up pretty good, it is WAY better off the line than the TH400 now with this setup converter included.

 

[GhettoRacingKid]

What kind of th400 did u get from summit? U really need to go with a well built th400. A "stock" or street strip willnt handle your power.

The 8.5 will last a while. If you really start hooking u can run the risk of bending the tube since they are thinner.

 

[ZZ4CutlaSS]

Burnouts are hard on transmissions don't Ya know! Just giving you a hard time....Sweet builds by the way! I'm on my second trans and I hope my 8.5 holds up also! Keep up the good work wish I would have went the LS route!

 

[LS1GN]

Transmissions seem to be my Achilles heel. This motor is really, really strong and the THM400 is only rated for 450 ft lbs and I think I am over that.

 

[-83MONTESS-]

Transmissions seem to be my Achilles heel. This motor is really, really strong and the THM400 is only rated for 450 ft lbs and I think I am over that.

My dad runs a stock TH400 behind his 550 lbs-ft 455 BBO. Has run it since 2003 with no issues. Only has a deep cast aluminum pan, street/strip shift kit and Hughes converter and I plan on running a very similar setup behind my 496. Sounds like someone screwed your's up when they rebuilt it to me :|

 

[84GP455]

Transmissions seem to be my Achilles heel. This motor is really, really strong and the THM400 is only rated for 450 ft lbs and I think I am over that.

If you haven't installed a transmission cooler I would recommend to. Heat kills transmissions not 450ft lbs. I have twisted drive shafts in half like a piece of licorice with my TH400

 

[LS1GN]

Thanks. I have a large cooler on there, plus the fluid runs through the radiator.