whiteboy

About a week ago I put in new leaf springs on my 98 XJ, they were pretty far gone. To the point that the tire was actually chewing up the fender when I had people sitting in the back. Therefore when I put in the new heavy duty leaf springs it actually lifted the rear a good 4 inches...

Well now when I accelerate there is a deep rumbling/vibration coming from what I believe is the drive shaft. Then when I ease off the gas it makes a quick rough cranking noise. It seems to happen the most frequently between 1500-2000 RPMs

I'm gonna start with replacing the universal joints and see if that helps, because I'm guessing over time as the leaf springs began to sag, these joints wore down and now they are wearing in the opposite direction. If anyone has experienced this before and fixed it then please correct me if im wrong, Thanks!

MountiansRcool

do u have SYE???

ZINGGG

At 4 inches of lift, you're going to need to modify the driveline or you are going to get the exact symptoms you are speaking of. You either need a transfer case drop (temporarily) but you will eventually need a slip yoke eliminator. Before you do one of the two, you're going to burn through ujoints veryyy often.

MountiansRcool

^^ exactly what he said. im at 4.5 and i have been fine with no Sye but very recently i have been getting BAD vibes at 50+ mph im going with the Iron rock Offroad Hack and Tap SYE, its one of the cheepest. then im going to need a new double cardon DS

PatriotGT

are you saying it's 4" over stock height or just 4" higher than before swapping springs.

salad

Yeah you guys need to read a lot more slowly... He replaced his springs with OEM, previously he was 4" under stock height. He did not install a 4" lift.

Replacing U joints is a good starting place. At 4" of sag your driveline would have been so flat that your U joints could've been rusted solid lol

jeepscottr1

I had the same problem rearmost u joint at the axle was pretty chewed up

ZINGGG

Ah, yes. You are right, sir. Everything he said.

I'm pretty sure the "heavy duty" leaf springs give you at most between an inch or two of lift over stock. At that height, you wouldn't need a t-case drop or SYE. So yes, check your u-joints

whiteboy

Thanks guys, to clarify it was sagging maybe 3 inches under OEM height, so replacing them brought them back up, and I believe the heavy duty grade gave them an extra inch or so, so its now slightly higher than it should be, but nothing drastic. Enough to make this an issue though, so I'll be replacing the U-joints this week and I'll post an update after that. Thanks again for the input, much more help than I expected

whiteboy

UPDATE: Replaced the rearmost U-joint, made no difference, and the front u joint seemed fine so we didnt do it yet. We did notice that theres a small dent in the drive shaft, but it must have already been there before we replaced the leaf springs, so it didnt have any effect on the way it drove before the rear was slightly lifted. Would it make sense for this slight dent to cause a vibration only after fixing the suspension? The shaft does seem straight however, just dented...

salad

It's very possible that now that you've tuned everything up the dent is making a difference. Technically it is throwing off the balance at the driveshaft, I wouldn't imagine that it would be severe though. Go for the front U-joint as well, they can look good but still be on their way out. Also have you packed the slip yoke with grease?

If you do all the above I'd take it for a spin without the front DS installed at all and see if that makes a difference.

Radi

Ditto. I've had more than one that looked just fine but found it frozen nearly solid after pulling the shaft and trying to move it by hand. They can take a "set", now you've changed the angle...

Matt_McKeehan_XJ_ATX

how difficult and what tools are needed to change out the u-joints? I have a very slight rear driveline vibe at 40mph or so after installing a 3" that's 3 inch only rough country lift with full rear leaf packs. Could be that once the rear packs settle, the vibe might go away, but I wanted to try u-joints prior to doing an SYE and rear drive shaft. What are the best u-joints to use?

whiteboy

I actually did remove the shaft to swap out the rear U-joint, and when spinning the front U-joint, it felt smooth and fully functional unlike the rear one. But I understand that any disruption inside it might only be revealed at high speeds, so I'm gonna swap it out anyway just to be sure.
I may actually just grab a whole new drive shaft anyway to be sure that the dent isn't causing any problems

89EugeneXJ

Have a drive line shop balance the shaft. Even a small dent could throw them out of balance.