OK, I have a newly rebuilt TH400 that the slip yoke will not slide on to. It appears the opening ID of the rear seal is to small for the yoke. I cannot get the shaft to slide past the seal. Is this a situation where some persuasion is necessary to get the yoke past the seal? Thanks Atomman
Should slide right in. There are a couple different sizes of yoke used on them, though, so make sure you have the correct parts....pictures and history help us help you
Have you checked back with the rebuilder? Was this transmission in the car before? It’s been a long time since I messed with a TH400 but I seem to remember that there were at least two different yokes, a small OD version for passenger cars and a thicker wall, heavy duty version with a larger OD for larger trucks and motor homes. That would mean that there is two different seals. Don’t force it, the yoke should slide in smoothly with moderate force if everything is right.
Short 4 inch tail housing? The tail housing should have a C on the casting of the housing. That is the common size tail housing. Buick used an odd size smaller ID diameter tail housing for a few yrs. Smaller ID bushing, smaller ID seal with a matching yoke..
The small diameter outside with the standard large spline, was used mostly on early Buick transmissions. But there are still some of those tail housings out there, I think I have one....if it's a transmission that was pieced together, maybe it got the small one? Or maybe the bushing was not installed correctly? or maybe the yoke is damaged? or something about a missing spline? There are lots of possibilities, and not much info to go on.
Buicks used a larger diameter slip joint. I had a driveshaft made for my Model A and had the same problem. Even though I told the guy that I had a Buick 400 and I thought they used a different slip yoke, he put the smaller diameter slip yoke on the shaft. When I went back he conveniently forgot our conversation. However, he did order and install the correct yoke at no charge.
There should be 2 different tailshaft housing diameters...3 if you count the turbo 375 which used a turbo 350 size output.
Yes, you need a later tail housing. Too new , and it will have metric threads for the mount. Hopefully not a big deal for you , but watch for it.
I have one of those goofy 400's in my 57 pickup, they call it a medium duty or some shit, 1967 definitely had that yoke. The o.d. is like a th350 but of course splined like a th400, a transmission guy said you can just change the tail housing and a regular fat th400 yoke will work.
Yoke is 32 spline 1.68" O.D. Shaft 4 1/2" long shaft U Joint: 1 1/8" cups 2 9/16" wide 3 5/8" end to end Inside clips All the standard th400 yokes are 1.88" diameter and use a 2.7" seal. Mine took a 2.5" seal. Apparently very few of these smaller housings/yokes are made
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