How do I know which trans to use? I'm replacing my 350 for a 455 in my 72 cutlass and I just picked up a posi rear. I have a friend who has a TH400 out of an olds but it's been sitting and should be freshened up. My question is, how do I know if I need a short tail or long tail on that trans and can I use the same driveshaft?
I'm assuming the same driveshaft as long as the trans measures the same length as the current one. Is it easy like that or am I missing something? I planned on using the TH400 since that usually came paired with the 455 although others have suggested a 700R4. Some have told me that won't hold up but regardless I feel more comfortable with that TH400 since that's what the factory used.

 

"A" bodies with 400TH were all short tail shaft as far as I have seen.
More than likely, your driveshaft length will need to be changed
depending on what transmission was originally in the car.
With a 350 engine, it is probably a 350TH.
Pretty sure length of the 400TH driveshaft will be different.
You'll definitely need to change the yoke on the driveshaft to the larger 400TH yoke.
Also, the cross member will need to move.
Usually, the frame will already be drilled for the 400TH cross member location.
The 400TH transmission is amazingly durable.
I've tortured several in years past and never "tore one out".
If the fluid in the transmission now looks good, odds are all that transmission
needs is new front and rear seals, maybe a front pump "O" ring
and a fluid and filter change.
I've taken 400's with some pretty "ugly" fluid, changed fluid and filter and it worked fine.
PM sent.