Thread: Need info on a TH400 to TH350 tranny swap

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I'm running a 327 Chevy with a TH400 Tranny. I noticed that the TH400 has a 4.9" output shaft, and the u-joint bolts directly to the shaft. Since I am going to use a straight driveshaft (no center carrier), it looks as though I'm not going to have enough u-joint coupling shaft length for it to slide in/out when the rear end moves up/down. I know that when you measure for a driveshaft length, you have to pull the u-joint out 1"-1 1/2" for play.

Is this a safe thing to do on this tranny?

Should I change to a TH350 with a longer output shaft, from a car?

If I do, will the torque converter from the TH400 fit the TH350?

Sounds to me (and I may well be mistaken) that you just need to make sure you have the correct driveshaft length. Rather than to do a tranny swap.

I'm not too concerned with driveshaft length right now. That can be taken care of easily when I have one cut to size. This Chevy eng and tranny are in a 52 Ford pick-up, so there's going to be some fabrications.

Again, my concern is with the tranny output shaft length. There will be no carrier in the middle. The slider will be at the end of the tranny.

Is 4" enough for a slider?

Should I bolt the u-joint to the output shaft and make the springs do all the work?

Should I swap it for a shorter TH350 with a longer output shaft?
(The tranny support bracket location is not problem)

I'll try to help you out here, but I seem to be very confused by what you've typed...

You're getting rid of the carrier bearing one the driveshaft... got that.

What are you talking about with a "u-joint coupling shaft"?

It sounds like you say your TH400 has a bolt on yoke. If that is the case, you need your driveshaft to have a slip joint built into it.

its got to have a slip joint in the shaft some where. far as i know it dont make no dif where its at, but its got to able to slip back and fourth.

SLIP JOINT...That's the part name I was looking for.

In a full size pick-up the u-joint at the transmission is bolted to the output shaft. The slip joint is at the center carrier. the u-joint at the differential is bolted in.

Since it's about 52" from trans u-joint to diff u-joint, why bother with a center carrier. I'd like to use a slip joint at the trans, and a one piece driveshaft, like in a car.

Can I use a slip joint on an output shaft that is only 4" long?

Since I can't find a TH400 with a 9" or 12" output shaft, should I opt for a TH350 with a longer shaft?

If I understand what your situation is correctly you have a PU tranny with a bolt on U Joint and no slip joint. This setup requires a 2 piece drive shaft with a slip joint where the the 2 drive shafts join.

As you have to have a slip joint somewhere (no you can't let the springs do the work something will break in a very ugly manner)and you want to run a 1 piece drive shaft so you need a slip joint on the tranny.

Unless you want to disasemble the tranny you have and change the output shaft to 1 that is designed for a slip joint (yolk), you need another tranny that is desinged for the slip joint.

The TH 350/400 came with different legnth tailhousings for different applications. I believe at least part of the reason for this was to help keep the drive shafts short in an effort to reduce vibration. Any of these set up for a slip joint will work. The amount of in and out movement of the yolk is really very short (usually well under an inch).

The main reason you need to pull the yolk out 1-1 1/2" is so you can push it in that amount for the rear U Joint to clear the rear end yolk to remove the drive shaft. Of course pulled out much more than that runs the risk of not full engaging the output splines and tail shaft bushing.

Basically find a tranny set up for a slip yolk and the yolk that goes with it and build your drive shaft.

Thanks Mike, that's the info I was looking for.

I got this TH400 for free. I guess a freebee is no real bargain if you can't use it... Tomorrow I'll look around for a TH350 with a slip joint for a one piece driveshaft.

Can I still use the same flywheel and torque converter?

Thanks Mike, that's the info I was looking for.

I got this TH400 for free. I guess a freebee is no real bargain if you can't use it... Tomorrow I'll look around for a TH350 with a slip joint for a one piece driveshaft.

Can I still use the same flywheel and torque converter?

you should be fine with your present flywheel and TC... TH400's are overkill in most applications anyway, the TH350 is much lighter and a bit smaller, making it easier to work with as well.

and for the record, YOKES are on driveshafts, YOLKS are good with pancakes.

Thanks Wrench, that'll save me some cash.

Went to the junk yard this morning, all I could find was a dozen or so 'RAPED' TH350s. You know, the pan removed and the innards all over the place.

I believe you're right Wrench. The TH400 is overkill for a small block daily driver. It's mostly used on pick-ups for heavy hauling like large boats and travel trailers. I read a thread on a different forum that the TH400 can rob you of horsepower.

The guy I got the tranny from went with me to help me pick out a good TH350. He kept harping about how I was making a big mistake by not using the TH400, that the TH350 couldn't handle the 327 Chevy engine. The clincher was when he announced that he was getting poor performance from his DIESEL engine, and he was going to upgrade his carb to a Holly 600, and a HEI distibutor.

I pulled over at a Convienence store, gave him a dollar, and told him to go buy me a newspaper. As soon as the car door closed, I took off like a 'bat out of hell', leaving him and the dollar on the curb.

Lesson learned!

nice.... I've seen TH350 trannies behind 700 honest horsepower... they never blinked an eye...

Hi,

It's a little late for this reply, but watta hell.


You can get a drive shaft that has the slip-yoke part in itself.

both ends hook up to a u-joint.
would have cost you about $200 and th400 is still a better choice!

i think all you have to do is get a 400 pass slip yoke and take the center bolt out of your 400 take you old yoke out and you are set the 400 takes power but is a very tuff trans

A little late guys, but still good info. I opted to change out the frame and use a Chevy S-10 frame. The 327 engine with a TH350 9" output shaft fits like a glove. Plus I got IFS, power steering, power disc brakes and lowering all in one shot. Right now the whole project is under a tarp...Handicapped In-Laws moved in. The only things I'm building now are wheelchair ramps and aides to help them move about the house. Don't worry, I'll get back to it around the first of the year.