I am rebuilding a 79 Camaro currently and I have a question.

I replaced the turbo 350 it came with with a turbo 400 and was wondering how long my driveshaft would have to be now. If you don't know of the top of your dome where should I measure from.

 

When installin the TH400 with a 8.2" rear, the driveshaft dimension from center of u-joint cap to center of u-joint cap is 55". If you are going to upgrade to an 8.5" rear, reduce driveshaft length to 53.5"

 

Um my 79 came stock with an 8.5" rear end.

 

You're going to have to move your transmission crossmember back also. The TH400 is a little bit longer. Bolt it up to the motor, bolt your motor to the motormounts, and then move the unbolted transmission crossmember back. Install it onto the transmission and then you'll have your guide holes for your drill.

 

http://www.bowtieoverdrives.com/cata...AT&CATID=YA1A1
That is a direct bolt in crossmember!

 

you still have the TH350 if so just measure the length of if from the bellhousing where it bolts to the block to the end of the output shaft, then measure the TH400 the difference is the amout you need to shorten your drive shaft. A good driveshaft person will do that and have them rebalance it.
you will also need to change the output yoke as its bigger, there are two different outside dia. of the yokes also, the one you need dependes on the rear seal, unless the trans came with the yoke, also the front u-joint will be different

 

a turbo 400 and a a 700r4 r the same thing but with a overdrive right? cause i might get that crossmember! i dont wanna go through all the bull**** of drilling my frame and breaking bits!

 

i put transmission in place and made a few measurements ,put the crossmember in place made a few more adjustments.got everything out of the way so i could have room to work.scribed some lines and punched a few holes.then i drilled the holes and i drilled the 1 1/4 hole on the bottom of the frame, so you can get a socket on the nut.it all went together perfect.you have to move it back approx.4 inches.i had to bent and drill the shifting cable bracket to make it work on the 400 turbo.with everything in place,pull the yoke out of the back of the transmission about 2fingers width.then measure from center of yoke at the back of the tranny to the yoke on the rearend,this should get you close enough on driveshaft length.summitt sales a driveshaft loop,i reconmend getting one.its all over if the shaft comes out and you dont have aloop.you have to buy a new dipstick and tube for the 400,the 350 is not the same.i think i payed 12.00 dollars for mine

 

I'm past all that with the install except the shift cable bracket. If the cable isn't adjusted right I've read that the gears won't be fully engaged and in a fewmiles irrepairable damage will be done. Also I might add that no one has mentioned the detente switch that goes on the accelerator pedal. The 350 has a cable where as the 400 is electric. The tranny will work Without it but you lose your top end and the whole reason for converting in the first place.
This is my 2nd conversion. My first was a 77. Everything bolted right up which leads me to believe that what I actually installed back then(20 years ago )must have been a th375 which is a th400 with a smaller output shaft. My question is after you drilled and bent the shift bracket, how did it b perform? My cable seems like it's too long now.

 

Welcome Topglass
Please keep an eye on the dates of posts you reply to. This site has been here a long time and the original post is from 16 years ago. Man there is a lot of bad info in this thread that was never corrected 16 years ago.

TH400 and 700R4 are the same thing?? LOL

FYI the wiring you are talking about is for the kick down of the transmission. This combined with governor pressure cause the rapid down shift and holds the shifting to higher RPMs under heavy throttle. It should have no effect on top end of the car or life of the transmission. You would also eliminate that when going to a manual shift valve body. Back in the day I use to rebuild transmissions but I have only done conversions to Th400 in street/track car when people wanted big blocks or wanted more the 450 ft-lbs of torque. Sorry to say I can not remember doing one of these upgrade in a car with a stock shifter. I also do not remember doing anything but hooking up the shift. A quick search shows after market shifter fit both 350's and 400's.

If you need the strength of the TH400 I strongly suggest a manual valve body. You can take a used TH400 in decent condition install a manual valve body, change out the pressure regulator spring and the accumulator springs and now you have a trans that will likely last a long time.

IMO the TH375's are not worth messing with unless you are looking for a core to start with. Even then to buy a replacment output shaft and the fact the output shaft is the last part to come out of the transmission its just not worth it. If I remember right they came mostly in station wagons and the output shaft is a built in weak spot for racing application. There is also a TH375B which is a heavy duty TH350 used in trucks. We used to use those parts to build the TH350 but aftermaket is so much better now they are not worth messing with.