Driveline help needed! Rearend swap -

[Wicked72ride]

I just recently replaced my 7 1/4 rearend with an a-body 8 3/4 rearend and I was wondering whether I should be using the same driveline? I have it in but it seems very tight in place. I havent dropped it off the jackstands yet - but would like a second opinion.

Thanks FABO in advance

Jason

 

[clhyer]

I don't think I would drop it down yet. If I am not mistaken, the 8 3/4 rear is a good bit bigger than your 7 1/4, that would mean the U joint yoke on the front is a lot closer to the tranny than it was with the 7 1/4. I believe you will need to shorten your driveshaft, or get the drive shaft from the other A body you got the rear from.
I am sure that others that have "been there, done that" will chime in for you.
C

 

[Wicked72ride]

how much shorter?

 

[ta3834bbl]

how much shorter?

I think it was about 1-1/2 inches shorter driveshaft , but that was a long time ago. take the shaft back out, jack up the axle into it's regular position then put the yoke into the trans . Pull the yoke out about 1" to 1-1/2" and leave it there. Now measure the center of the ujoint cap in the yoke to the rear axle center of the cap and tell the driveshaft shop to make it that long. You need the 1" at the trans so when the suspension rises and falls it won't bottom out into the trans. Guys, help me out with the slip yoke. It is supposed to be 1" to 1-1/2" right ?

 

[SGBARRACUDA]

Drop the rear of the driveshaft, jack up the rearend to put the weight on the springs, then try the driveshaft. It will be to long, measure how much needs to be taken out of the driveshaft to leave One inch of slide on the front yoke.

 

[SGBARRACUDA]

I think it was about 1-1/2 inches shorter driveshaft , but that was a long time ago. take the shaft back out, jack up the axle into it's regular position then put the yoke into the trans . Pull the yoke out about 1" to 1-1/2" and leave it there. Now measure the center of the ujoint cap in the yoke to the rear axle center of the cap and tell the driveshaft shop to make it that long. You need the 1" at the trans so when the suspension rises and falls it won't bottom out into the trans. Guys, help me out with the slip yoke. It is supposed to be 1" to 1-1/2" right ?

Beat me to it. I'm a slow typer but your dead on.

 

[Bad Sport]

Yup, if you went from a 7 1/4 to an 8 3/4 you will have to shorten and balance the shaft. Insert the slip yoke into the trans until it bottoms out. Pull it back an inch and see what the difference is.

I would suggest you find a local shop and call them and ask exactly what they want for measurements. Some shops will want one thing while others will want it done a different way. Whatever the case you will want the suspension loaded.

You will damage the transmission if you leave it like it is. I had mine cut, balanced and they installed my u joints and cleaned and painted it for 90 bucks.