1fast bird

iTrader: (22)

Is there a certain year th 400 that I should look for?I need a super strong transmission to hold the power I wanna run in my formula.I'm considering buying and rebuilding my own 400 for light street/strip duty.I know a lot of people are running 400's in there ls1 powered cars.What should I look for in a th400?Will any 400 bellhousing work (I know some bolt holes won't be used)?
Thanks,
Chad

9000th01ss

iTrader: (10)

Any year will work.
It has to be a chevy bolt pattern.
For tail shafts look for a 32 spline 4 inch housing, or a 27 spline 9 3/4 housing.
I'd get the newest one you can find and upgrade it with a 4L80E direct drum with a sprag instead of a roller clutch.
That and a standard high perf rebuild should hold 600 hp IMO.

As for what not to get, don't get one from an Buick/Olds/Pontiac/,Rolls Royce, Jeep, etc.
Don't get the cadillac one with the super long 32 spline tail.

Edit: avoid switch pitch th400's, although they are near impossible to find in junkyards these days.

forcd ind

iTrader: (7)

if you find an hd case all the better-you wont find a switch/pitch 400 in a chevy pattern, unless it was converted-i love my switch/pitch 400 in my ls chevelle, dual stall, works great, but as said, hard to find parts
i think 68 up went to a 34 element sprag, and also used a thin spacer to protect the case-there is a tag on the side, has the year, and also letters what it was behind

9000th01ss

iTrader: (10)

Actually '70 up went roller clutch. Doesn't make sense to me to buy a '70 or older just for that when that part can easily be updated.

HD on the top of the case means nothing as well. My friends dad had a 1988 GMC Sierra 2500 bought right out of the lot in '88, 13 years later I built that trans and it was no different than any other. Actually the seperator plate was the only difference, no straight cut gears or nothing.

formulajunky

good info i was looking into this the other day.

jakeshoe

iTrader: (14)

The HD or "K" case has a bolt on cast aluminum flywheel cover that adds strength to the bellhousing.
87-up has a different seperator plate.

Pre '71 units have the smooth inner race on the direct drum.

The best ones to use are the later 70's-late 80's truck units.

You have to be aware of the output shaft differences when using the truck units.

Straight cut gears were in the 475's used in RV's, etc. The helical gears are actually stronger, so straight cut gears are a waste of time in most applications.

9000th01ss

iTrader: (10)

I've seen very few with the thick aluminum flywheel cover, they're usually gone. The bigger bolt holes were there. I did not know this.

I noticed the HD units have the same sep plate as the B&M shift kit, thats why I don't use that kit.

jakeshoe

iTrader: (14)

The HD trans don't use the same seperator plate as B&M. B&M anodizes their plates gold and it has a B&M part number. No GM trans came stock with this plate.
If it has a gold seperator plate in it, someone has been into it before.
The B&M plate has some differences in the accumulator feed holes from a stock one.

I don't like the B&M kits. If installed by the instructions they cause parts breakage. Very poorly engineered.

On a TH400, there is no better bolt in kit than the TransGo Reprogramming kit. The TransGo kit dual feeds the direct clutches, which really helps them to live longer in performance applications. The TransGo kit will shift harder than the trans needs to be calibrated if set on the upper end of the TransGo instructions. No other bolt in kit makes this modification on a TH400.

However,
If you are over 500 HP on a TH400 or a 4L80E, the only real solution is to do the internal dual feed modification. The TransGo method is good but not good enough for bigger power.

9000th01ss

iTrader: (10)

Why do people take things I say so literally?
I know no GM transmissions came with B&M kits.
MY POINT you buy a B&M kit and set it up following their directions, you end up with a plate just like the one you took out. Except you have the option of drilling the feed holes WAY too big. You ALSO have the option to drill the accumulator holes to near stock sizes.

I never built an automatic th400 without a TransGo 1&2 kit. I'm a bit sensitive in the area of someone thinking I put B&M **** in anything, sorry.
Heres proof just a box full of the spare VB gaskets that come with the 1&2 kit.
In fact second pic is a box of brand new parts in the garbage out front right now.

jakeshoe

iTrader: (14)

The B&M plate is OK to use if you need a plate since GM doesn't service them anymore. I'm not sure if there is anything even available on the aftermarket.

I quit using the TransGo kits because almost every TH400 (or transmission) I build is for 500+ HP so there isn't any reason for me to use them.

The way you made it sound as if they came with the B&M plate.

Some of the factory plates have a very large 2-3 feed.