reading through performance catalogs i noticed some heavy-duty parts for th-400 transmissions such as heavy duty sprags(or sprag bearings)and some other things i can't remember.the manufacturers and/or sales catalogs say these are weak points in the th-400.is this an exaggerated sales gimmick,or should i consider buying? at what power levels does this become necessary? my project is seeking 575 horsepower and over 500 lbs.torque.from a 385 stroker street/strip car.can someone tell me what internal tranny parts need to be beefed up? thanks.

There are some things to look at. First make sure your trans has an early drum in it so you can use a 34-element sprag for 2nd gear, which is a must. The only other things I like to do in a 400 are to carefully inspect the hardparts and replace what is bad, and also I replace the rear thrust washer setup with a Torrington bearing and set the endplay using shims at that bearing. I also prefer to use a Spiroloc instead of a snapring for retaining the sprag plate, so it will not pop off like sometimes occurs. The two things to look very closely at for wear are the front pump, and the reaction carrier/rear band. The rear band applies for reverse and often the surface of the reaction carrier gets worn pretty badly, so they need to be replaced possibly. And, use a decent overhaul kit along with whatever choice you make for a shift kit or complete valve body. That is about it! If you need any parts shoot me an email, it will be worth your time and $$$!

I have been using a TH400 on a street/ strip car for more than three years. I have lots of 1/4 mile passes on it. I removed it and had it inspected last Spring when I changed converters. There was no sign of any wear and it has worked flawlessly. I push about 530 hp through it. When on nitrous (100hp hit). The only downside is that they eat more horsepower than the TH350. It should not be a problem with your 500+ ft lbs. of torque. graemlins/thumbsup.gif

Steve won't steer yoo wrong Bowtie.

Inspect the areas he mentioned.
The direct drum is what the intermediate sprag is attached to and brings to a stop for 2nd gear...

It is a heavy element in the trans and bringing from 80% engine speed to an immediate stop on the 1st to 2nd shift is harsh, particularly if the trans is setup to shift VERY hard.

I would say your borderline on the necessity of the 34 element sprag.
I usually recommend about the 450 lb ft level moving up, but I have TH350's out there living under more with an equally weak stock intermediate sprag.

The sprag is pretty inexpensive about $50, but the drums are hard to find.
Your core MAY have one, if it is an early unit or ever been changed.
A direct drum from a 4L80-E is interchangeable and will use the 34 element sprag.

Key here is to use a shif tkit that doesn't breka parts.
Steve can hook you up with a TCI or you could use a TransGo that is my preferred kit.
They are both similar but the TransGo dual feeds the directs.
You could also dual feed the directs internally if you use the TCI and rebuild it yourself.

Good luck

thanks for all the fantastic input guys!several years ago i had a trans rebuild from MR. TRANSMISSION in hoover,alabama.i requested that my sprag be replaced with a heavy duty unit and if anything even looked dull i wanted it replaced.i also had them to set it up for ultra-hard shifts.boy, did they ever!everytime it shifted 1-2 it tried to throw me in the trunk!when i asked what they did,they said they drilled a coupla holes in the valve body.do you guys know anything about that trick? anyhow,after i blew a head gasket 7 years ago,i removed the motor and have had the chevelle in storage since then.now i'm working on getting her back in action.is there a code number somewhere on the trans that will tell me what year it was made? by the way,steve,i'm sure i'll be doing business with you in the future. graemlins/thumbsup.gif its obvious you are a hardcore gearhead!i saw your website.. :eek: