2000 XJ here, 248K miles. When I accelerate from a stop, I can occasionally feel a "thump" from the back end. I would compare the feeling to having something heavy in the trunk that slides backwards into the rear door when accelerating. Any ideas? I haven't really looked under the rear in a couple months, just wondering if anyone has had a similar feeling or know of any common issues related to this.

I appreciate any help!

 

Pull the differential cover and check for broken gear teeth.

Check your leaf spring mounting points too.

 

I recently opened up the rear diff. and cleaned it out, since I was getting a humming noise at right around 45mph (not slower or faster, just 45mph). I sprayed it all down with cleaner and refilled it with oil. Everything looked fine in there.

I'll check the leaf mounting points today. I know the springs are terrible and need replacing, which I'm sure isn't helping anything.

 

That happened with my dad's FJ Cruiser, It was shipped from the factory with a driveshaft that was a little too short (service bulletin "to be repaired only at owner's request"). Assuming this happens on both start moving and right at stop, I would check your drive shaft and make sure it is still as it should be and hasn't moved over the years. My 2000 hasn't done this yet. My leafs need replaced too, should do it this winter but will probably have to wait until summer.

 

Check rear lower shock mount nuts for tightness. I had this same thing and it wound up being a slightly loose shock.

 

I had an issue related to this, same feeling but from braking. Every time I would use enough brake power to engage the drums it would slam like the axle was moving, turned out to be worn hardware and pads, replaced them and it all went away. If it's from accelerating only it might be the u bolts too or axle wrap if you're slamming on the gas.

 

Fix for the bowling ball in the trunk:
Remove the rear drive shaft lube the slip yoke splines with a little anti seize and reassemble.

 

But what if it really is a bowling ball in the trunk?

 

I refer you to the infinite genius of Queen & just tie that mother down!

 

I'm having the same issues, so I'll have to check the rear shock mounting points and driveshaft. It does it mostly after braking to a stop and hitting the gas to get moving. It feels like the axle is moving and binding or the driveshaft. Left rear brake is very grabby, so that could be making it worse.

 

Absolutely. Probably dry as a bone behind that rubber bellows.

 

Any details on how to pull that joint apart?

 

I wasn't aware that there was so much clearance between the splines. I'll check it out this weekend. Is there a more convenient end to remove? (I have never looked at it so I may be asking something obvious here)

 

Anti seize is for non moving parts like nuts and bolts that are subject to rusting thus making them hard to remove. Use a grease made for chassi and driveline.

 

It's a slip joint. Disconnect the driveshaft @ the rear axle, tape up the bearing caps if you need to. Then cut the metal clamps around the rubber bellows and pull the driveshaft straight back. Have someone or something catch the front when it drops.
Folks report anti seize lasts longer than grease, that's why you see it recommended even though it's a nonstandard use.