TH400 to 4-speed Driveshaft

I am working on a conversion from TH400 to Muncie 4-speed. Will I have to change the length of the drive shaft?

 

yes, the th400 has a longer tailshaft the the 4 speeds,if you had a th350 it would be a direct match-up, so easiest thing would be to find a th350 car and get the driveshaft out of that.

 

Didn't anticipate that. Amazing how the budget just grows and grows. Can the shaft be cut down?

 

Don't quote me on this but I would hold off on modifying the driveshaft until you have your 4 speed tranny in place. The reason I'm saying this is because I recently did a conversion on my '70 cutlass. Car originally had a 350 engine and 350 tranny. I dropped in a 455 engine and super t10 transmission which looked to be the same dimension as the muncie m21 that I was originally going to use (I did not do actually measure them with a ruler). I figured that my original driveshaft would fit and it turned out to be too long. I measured how much I needed to cut off and had it shortened. When all was done my driveshaft ended up being the same length as the one in my '70 skylark with a 455 engine and 400 tranny. I know when I bought the 4 speed setup the guy gave me the driveshaft (350 motor m21 tranny) that supposedly was in the car and that also was too long.

Allen

 

The front yokes are also different diameters for TH 400 vs TH 350/4-speeds.
Duane

 

Thanks for the info. I guess the rule applies, measure twice, cut once. Makes sense to wait and measure.

As for the yoke, I figured that to be different. Aside from the diameter, I think it has a different spline count.

 

I have a brand new driveshaft for a TH350 car WITH a yolk and ujoints (I believe it a 28 spline)...

Dimensions as follows:



This was ordered thru YearOne for my 66 Special, which is now long gone. Make me an offer if interested. I can get you pictures, and I'm pretty sure those measurements are correct (they were from a few months ago).

I paid over $300 for it new ou:

PM me with an offer if interested (or trade for 455 parts)

 

Factory driveshaft will have to be longer if installing '63-70 Muncie (small output) 4spd in place of Turbo 400.

Using a large output Muncie used in select '70 Chevy products & in all '71-74 GM A-bodys & F-bodys, you should be able to get away with same length driveshaft.
:3gears:
Roger

 

So who's right? Some here are saying it needs to be shorter, others longer!