th-350 to th400 in C-3

[Tom Sarno]

I removed the small block and th-350 from my '74 years ago and used the th-350 for another project. Now it is time to put the drive train back in and I have an extra th-400 laying around. It looks like it is the same length, but it has a bolt in yoke. Could I use this trans with the bolt in yoke or will I have to find a new yoke? Is the cross member the same for the 350 and 400? Also would anyone have the overall length so I can check that it is the right size

[Joe L.]

Re: th-350 to th400 in C-3

Tom-----

First of all, someone else must have installed the THM-350 that you removed from your car years ago. No 1974 Corvette was ever originally built with a THM-350----all of those with automatic transmissions were built with THM-400, regardless of whether they were small blocks or big blocks. The first use of a THM-350 in a Corvette was for the 1976 model year

I don't know exactly what you mean by a "bolt in yoke". However, I can tell you that the output yoke for a THM-350 is different than the output yoke for a THM-400.

The crossmember is the same for both THM-350 and THM-400.

The Corvette THM-350 and Corvette THM-400 are the same length. I believe that all Chevrolet THM-350 and THM-400 are the same length, but this length does vary for other GM cars.

[Mark #28455]

different length TH400's

There were two basic lengths to the TH400 - "short tail" and - you guessed it, "long tail". Don't worry, Tom, the length difference is OBVIOUS (about 6 inches or so) so if it looks the same length it will work. In addition, for one year only (I think 1965) the TH400 was available with a small output shaft (same size as the TH350) but it's unlikely you'll ever see one. The only visible difference on a Corvette vs other Chevrolet application is the riveted on tag with the 2 letter application code, so swap away! (Buick Olds Pont Caddy TH400 has a different bellhousing).

A word of warning, some newer trucks used a "bolt on" yoke - I once got stuck with one from a late 80's one ton truck - should have known when I saw a bolt in the center of the yoke DUH!, the splines on the output shaft didn't allow my slip on yoke to slide all the way in. If your slip on style yoke goes all the way in to where it nearly bottoms out against the seal, you're ok. If it stops about 1 or 2 inches short of the seal, you better check things out.

Hope this helps.

Mark