I have this somewhat loud, definitely forceful thunk at the rear of my 2001 Cherokee Sport 4WD when I hit bumps at high speeds. The issue isn't consistent and my mechanic can't seem to replicate the issue often enough to identify a fix. I've replaced sway bars and links up front (no more death wobble!) and shocks in the back.

There are two ways to describe what's going on. First is the thunk sound. It sounds and feels like the whole frame comes detached from the axle on some bumps (not all), and then slams back in to place. It seems to be exacerbated when I'm accelerating, but not totally sure. Last night it made it's loudest sound yet when I drove up and in to a driveway at and angle that caused the whole vehicle to rock (as would be expected).

The second way to describe the issue is it almost feels like the whole back end drags or hesitates just a touch when I hit bumps, almost like I'm pulling a trailer.

Any thoughts or help would be appreciated. We have not cracked open the differential yet, and I'm almost starting to suspect something there or with the axle. Mechanic can't see or feel anything loose or unstable. Thanks!

Kurt

 

Did the mechanic consider things like leaf springs or transmission mount? You're implying he did, but I'd go a bit further and explicitly confirm that he checked. Also, if your rear spring bushings are worn, they might not -appear- to be that bad, but after replacing the control arms (other end of the Jeep, but same idea as far as bushings), I had a noticeable improvement in stability despite the old bushings appearing to be OK.
Also the torque specs are important on all this stuff, so again, sounds like this was checked but it doesn't hurt to get explicit confirmation.

Another thing that is often overlooked is to check the tire jack under the rear seat. I had a clunk that seemed to be drive line related going over bumps and it was nothing but the heavy jack (not sure what the factory setup was, but the one in there was a hydraulic bottle jack) bouncing around. That wouldn't explain the hesitation thing, but it's definitely worth the minor effort and few minutes to double check the "easy" stuff before pulling the diff cover. Gear oil reeks and just to look at the diff, you're basically doing a gear oil change even if the diff proves to be in perfect shape.

 

That sensation is "binding". And although that could be coming from within the differential, the two most common things to check first is the drive shaft slip joint and the drive shaft u-joints. My guess is the slip-joint is binding as the axle goes up and down. Usually, all that is required to fix this is to drop the drive shaft and re-lubricate the slip joint with grease. Provided the slip joint has not developed wear (play). I had the similar symptoms you described, though not quite as severe, and a general servicing of the rear drive shaft (both u-joints, and lubing the slip joint) resolved the problem completely.

Can I assume that you are in 2H mode when this is happening? Because being stuck in 4HI (part time) can cause similar sensations due to speed differences between the front and rear axles. If you are sure you are in 2H mode, or 4H (full time), this should not be the problem.

 

Excellent point. Again, another simple thing to check and is a routine maintenance item anyway, so definitely lube your slip yoke.. lol.

 

Ha! Thanks all. I will definitely have these looked at. And yes, this is in 2H all the time. I very rarely use 4WD.