Transmission Troubles

[mikajo39]

Okay here goes, I bought a TCI th400 streetfighter for my truck( http://www.summitracing.com/parts/TCI-211000/ ) , Originally had a Th400 in it, but rebuild prices are sky high in my neck of the woods so I bought the TCI unit new for less than the rebuild price. It works good and doesn't leak, except where the driveshaft yoke goes into the rear of the transmission. It's quite a bad leak and it's definetley not driveable like this. The yoke looks like its not engaging all the way into the back of the tranny, and it doesn't look snug. Do I need a new yoke? You can see all the spewed tranny fluid too

[Hart_Rod]

Is the rear seal messed up? Does the yoke have grooves or flat spots keeping it from sealing?

[Longhorn Man]

jack up the rear, and pull the shaft out. Look at the yoke, the part that rides on the seal. They are often times worn down a little bit, a groove almost. Also, rust in that area will cause the seal to leak too.

[mikajo39]

It looked clean when I put it in, but I didn't really take a look when i put it in. The seal shouldn't be messed up, it's new, but just because it's new doesn't mean it's perfect I guess. Going to be a few days before I can get back to work on it. You can shake it and move it around, like it's a little bit loose. It doesn't rotate though which is good but it just doesn't feel snug

[Hart_Rod]

Originally Posted by mikajo39

It looked clean when I put it in, but I didn't really take a look when i put it in. The seal shouldn't be messed up, it's new, but just because it's new doesn't mean it's perfect I guess. Going to be a few days before I can get back to work on it. You can shake it and move it around, like it's a little bit loose. It doesn't rotate though which is good but it just doesn't feel snug

I hate to ask this, but are you sure it's the right yoke?

[mikajo39]

Wellwhen I ordered the transmission I made sure it was the same stuff as the old one 4" tailshaft slip-on 30spline yoke same as the old on, still seems wrong though

[chevy_mike]

From what I can see in that picture, the lip on the seal is not even touching the yoke. What I have found is our year trucks are different then other T400, in regards to yokes.

I had barrowed a T400 yoke from a buddy, so I could use as a plug when I pulled the tranny. It was way bigger in diameter then my stock truck one. It would be the right size for the seal you have currently.

My guess is you need to swap the rear seal for the correct smaller diameter one and you'll be good to go.

As for your yoke engagement, you look fine. You don't want it to bottom out on the output shaft or you could do damage if/when the yoke slides in when the suspension cycles.

Hope that helps.

[turp mcspray]

Pull the driveshaft and count the splines on the trans shaft. I believe the 400 has 32 splines and the 350 has 27 splines. Some 400's used the 350 style with 27 spline. This is what it looks like from pics. you should be able to measure OD of yoke and find a seal to fit the 400 with inside diameter to fit your yoke. If you have a store that specializes in bearings and seals (around here it is Whisler Bearing) They will probably be more helpfull than the high school kid at Checkers. (no offense to all the high school kids on the board,It's just an experiance thing)

[kwmech]

Judging from the pic, he has a 1310 u-joint yoke and the builder installed a 1350 u-joint seal

[JP2120]

I have built many of these 400's and have seen this many times. The small seal is for the THM 375-400. This is a light duty 400 and uses the smaller seal. These are still good transmissions but are not recommeneded for drag strip use. I have used them in my drag car when I was in a pinch and it worked fine but I only ran about 6-8 passes.
Just thoght I would add my 2 cents. Good Luck.
Duke

[JimKshortstep4x4]

The TH 400 had two different extension housings. The older ones had a smaller diameter bushing and seal to fit the smaller yoke. Later ones have a larger bushing and seal to fit the larger yokes.

The larger housing has a bushing/seal hole that is approximately 2" in diameter and the smaller has a bushing/seal hole with a diameter of approximately 1 5/8".

You will either have to change your yoke to the larger yoke or change the housing to the smaller yoke that you have. Either way the yoke has to run in the right size bushing with the right size seal.

Jim

[JP2120]

Originally Posted by JimKshortstep4x4

The TH 400 had two different extension housings. The older ones had a smaller diameter bushing and seal to fit the smaller yoke. Later ones have a larger bushing and seal to fit the larger yokes.

The larger housing has a bushing/seal hole that is approximately 2" in diameter and the smaller has a bushing/seal hole with a diameter of approximately 1 5/8".

You will either have to change your yoke to the larger yoke or change the housing to the smaller yoke that you have. Either way the yoke has to run in the right size bushing with the right size seal.

Jim

I concur with Jim. The houshing will be cheaper at the Transmission parts supply house about 20 bucks. You better clean up that yoke though. I see rust where the seal is going to ride. Use a really fine emery cloth 600-1000 grit

[mikajo39]

I have my old transmission and its completley dissasembled. Could I take the old housing and bolt it onto this one?

[Richard H.]

Your answer is in post 11 , which is yes you can. You have a 1350 housing on the tci and need the 1310.

[mikajo39]

Woo thats good news glad I kept all my parts and stuff. Thanks a lot guys really appreciate it

[Richard H.]

Now might be a good time to make sure the speedo gears are the same also, if not swap it too.

[mikajo39]

Eh they've always been around 5MPH off it doesn't really bother me much.

[mikajo39]

So, I am about to head out tomorrow morning to figure out how to fix this, Is it as simple as it looks? take off the housing and replace the bushing and seal or should I just get a new yoke and not dig into the tranny? Opinions welcome

[JimKshortstep4x4]

If your yoke is worn then it should be replaced. There can be a difference in lengths on new yokes which could cause a problem so be sure to check differences.

There are only 6 bolts holding the housing onto the tranny and it can be resealed with silicone. Fluid running out is a consideration but if the rear is jacked up higher it will help.

Costwise a seal and bushing are probably a lot less then a new yoke.

Jim