driveshaft/pinion angle saga

[1stseries55]

need some opinions:

I am swapping a rear end from an 87 burb into my 65 GMC(leaf spring truck)

I moved the rear back approx 1" to compensate for flipping the rear above the leaf springs

with the move rearward the driveshaft still does not fit, it's close but the pionion angle would be off and the yoke is bottomed out in the tranny

I have to have the driveshaft shortened some...question is, how much?

I would think the yoke needs at least an inch to travel... then i need another 3/4 to 1 inch to set the pinion angle correctly.

so the yoke itself is 4"s long.... if i shorten the driveshaft 1.75--2"s will the 2" remaining in the tranny be enough?

what do you guys think? anyone done this on a leaf spring truck have any suggestions?

here is a pic that really is irrelevant but hey, we all like pics

[shrunken66stroker]

When I had mine shortened I called the shop that was doing it for me and they gave me specific instructions on how to measure it. Put the truck at ride height. Measure from the rear of the transmission, not the output shaft but the back of where the slip yoke slides in, to the flat part of the pinion flange on the rear end. They then had me subtract an inch and give them the number. Call your drive shaft shop and ask them. Everybody has different ways of doing things and they probably will too. As far as pinion angle, I've always heard 7 degrees at ride height. Don't quote that one though. good luck.

[Imperial Kustom]

Yikes! 7 degrees! No! No! No! Having worked at a driveline and differential shop for many moons, that is not right! Zero at the rear yoke is the magic number, BUT, you need to compensate for spring load while driving. Pinion angle should be 1.5 degrees down at ride height. And yes shrunk, that is the correct way to measure driveline length. From the output seal on the trans to the flat part of the yoke (where the bolt or straps go in).

[502tripower]

I think this will help. http://jniolon.clubfte.com/driveline...nephasing.html

[Imperial Kustom]

Ive seen that formula more times than I can count. It always seems to cause vibration issues. We've been setting our drivelines up the same way I described for decades, and alot of them finally come back to be serviced after decades still wearing our 25 year old sticker on them. Not bashing, just saying that it has always worked very well for us.

[1stseries55]

thanks for the response guys....

as you can see I do not have any weight on the frame ... when measuring how do I compensate for that? With more weight, the rear will move right?
Is it enough to make a difference?

thanks

[loco64]

hey imperial. what if you have a four link? Do you want 0 at ride height or 1.5 down still . thanks

[shrunken66stroker]

Originally Posted by Imperial Kustom

Yikes! 7 degrees! No! No! No! Having worked at a driveline and differential shop for many moons, that is not right! Zero at the rear yoke is the magic number, BUT, you need to compensate for spring load while driving. Pinion angle should be 1.5 degrees down at ride height. And yes shrunk, that is the correct way to measure driveline length. From the output seal on the trans to the flat part of the yoke (where the bolt or straps go in).

Thanks for following up. Sorry for the misinformation. Like I said, don't quote me on that one. I'm glad you saw that and obviously have more experience than I do with drive shafts. Where the hell did I get 7 degrees? hmm.

[Imperial Kustom]

Loco, I'd still shoot for 1.5 degrees.