Auto Trans swap

My 66 GS has a 2 speed tranny, and the 401 motor, I want a 3 speed, can I bolt up the turbo 400 3 speed from a Buick, Pontiac or Olds without any mods?

Ron

 

I believe you'll need one with the Nailhead Bell Housing.

 

Would that be hard to find? Would any of the retailers have this in stock, Summit or Jegs someone like that?

 

Not a chance.....

But post in the wanted section here. You'll find one.

 

I just did this swap in October. You will need a trans from a 65-66 full size Buick 401-425 ONLY. LeSabres with the TH400 have the wrong bolt pattern.
Also make sure that you get the complete dipstick setup as it is specific to the nailhead trans/block.
It will also be necessary to fabricate brackets on the frame of your GS so that the trans crossmember can be bolted in the correct place for the TH400.
Driveshaft will need to be shortened approx. 1 inch. and you will need the yoke off the full size Buick driveshaft as well.
You can use a later TH400 yoke, but will need to replace the trans output shaft housing with the larger diameter housing if using the larger trans yoke.
I can provide you with more details if you like.
It was not a difficult swap, but you need to make the above changes.

Mark