jerardisflossin

Hello, I have a 90 that we swapped in a 8.25 and its running 4.5" lift and a 1" t-case drop. After first doing this we noticed a loud thud over large bumps and because of the longer housing of the 8.25 versus the D35 we thought the driveshaft was too long. I swapped in a shorter driveshaft and I still have the same loud thud when going over very large bumps. What do y'all think the cause of this is? Could it be the driveshaft u-joints binding? Is there any fix to this besides a SYE? I see a lot of people are running this same lift and t-case drop and they don't seem to have this issue. Thanks!

burg3rlicious

How sure are you that it's driveline related? Is the axle shimmed?

jerardisflossin

I imagine it has to be driveline related as all that changed was the lift and rear axle. The axle is not shimmed, should it be even though I am not running an SYE?

burg3rlicious

It can't hurt. Even though you dropped the case the driveshaft angle isn't at stock, shims help get it a bit closer. Cheaper than an SYE too

jerardisflossin

Anybody else have any opinions? Im going to try some shims here shortly.

Guntar13

For what it's worth mine is at dead even 6 in the rear, double cardone shaft, shims, sye, and shackle relocation, and rustys heavy duty crossmember with 1 inch drop. No driveline vibes. Try the shims they do help

sycoglitch

You took the Ds that came with the 8.25 right. Did you ever rebuild it. How was the condition of the grease boot and output shaft. You checked all these things with a good noggin pokin I presume right

jerardisflossin

Unfortunatly the DS didnt come with the rear axle when I got it so I had to source a shorter DS. I swapped in one that was about an inch and a half shorter. I didn't replace the joints but there was no play in them and they seemed to be in decent shape. The output shaft had slight surface rust from sitting but otherwise nothing out of the norm.

Im really stumped as to what the thud could be. It sounds terrible (like something broke terrible). I look under the truck and the angle of the shaft at the pinion and at the t-case clearly differ but I really don't feel much vibes. It really feels like the shaft binding but I figured I'd see noticeable damage to the joints, no?

sycoglitch

When you look at the output shaft, how much does the DS cover it. Take pics of angles (2), I'd you grease inside the DS slip yoke and the output shaft (3).

caronaxtr

From what I noticed in my jeeps is a single "thud" sound really isn't a driveline sound. I'd double check all bolts, even ones that you didn't touch. Motor mounts in good shape?

I've got some vibes after the swap, but they are deff. Driveline vibes.

sycoglitch

There's a good chance the u bolts aren't tight. But might as well get DS off his mind. I get a thud cause my leaf spring eye sleeves move around from time to time. OP, what hardware did you use for u bolts, center pins condition etc. and is there play in the axle pinion. Did you open the "new" axle and inspect all

jerardisflossin

Here are some pics of the driveshaft angle at the t-case and pinion. After looking at it more it seems the angles aren't all that bad.

jerardisflossin

I will try and tighten those u bolts down. It literally did it as soon as we drove off once the lift was installed so I have my doubts :-/

Ill also check the pinion tonight!

Fred/N0AZZ

I will tell a few things about mine it came with a CHY 8.25. I have a 4 1/2" lift and to do it right needed an SYE/Shims/Adj. U&LCA's for the front and I bought a new driveshaft for the rear.

You did buy the correct u-bolts for the Chy 8.25 when you swapped it in didn't you.

sreeb

Put a cable tie around driveshaft at the slip joint. You will be able to see how much travel you have used.