Cutting a Driveshaft question

[Lee]

Hi

I am starting the install of an Advanced Adapter overdrive unit into my 1970 Highboy with a NP435 and divorced Dana 24.

I will have to relocate the tranny back 7 1/2 inches. This means I will also have the short drive shaft that goes between the tranny and transfer case shortned 7 1/2 inch.

This will make this short shaft even shorter.

Since the angle of this shaft is pretty straight anyway, do you see any problem shortening it?

Thanks,
Lee

[BobbyFord]

I always like to have driveshaft mods done at a driveshaft shop so I know the shaft is true and balanced.

[averagef250]

In short, yes, making the center shaft shorter exaggerates the issues with a divorced transfer case. The shorter the center shaft is the more extreme the U-joint angle changes become when the transfercase moves around under power- And they move around a lot. To explain a bit more- When you put a lot of torque through the t-case it tends to move forward at the bottom. This raises the t-case input a couple degrees which effects the center joint angles. With a long enough shaft the changes aren't bad, but when you get an itty bitty short guy in there you can have a 4-5 degree angular mismatch between the U-joint at the transmission and the one at the transmission. That's pretty bad. 1 degree off isn't very noticeable. 2-3 degrees vibrates and the effect goes up exponentially with increased misalignment.

The best you can do is mount the t-case on poly mounts and add a strut from the bottom of the t-case to the frame somewhere (something can give a little so you don't break things when the frame twists).

If you plunked down the coin for a Ranger overdrive I wouldn't see why you wouldn't have a driveline shop shorten the center shaft. Drivelines are fairly straightforward to shorten with simple tools you may or may not have, but you should have a solid understanding of the process and what alignments are critical if you do tackle it yourself. Go about the wrong way and you can easily make the tube ends unusable/ the whole thing scrap.

I would have bought a new NV4500 and mated it to an NP205 and made 2 new driveshafts in lieu of the Ranger route.

[Lee]

Thanks for the input Fella"s!!!

I will have a Driveline shop short'un the shaft. Also, Thanks for the note concerning the Transfer case strut. I will find/Fab one up.

Lee