My '96 XJ has started making a clunking noise when under load and while initially accelerating. It started when I was off roading and I was in 4Lo going up a loose, rocky hill. The clunking was erratic and sounded a lot like a loose rock slipping out from under the wheel and hitting the underside of the rig. At that time I didn't notice anything in 4HI or 2HI. I thought it was a front drive shaft issue untill I was accelerating from a stop sign today (pushed the gas pretty hard) and it made the clunking sound again. Now I think it's a rear DS U-Joint or my t-case. Can anyone shed some light on this?

 

i think ur on the right track. sounds like a u joint to me

 

Thanks. I was reading something on NAXJA about the rear yoke on the t-case being external on some models so they sometimes need to be lubricated. Mine's a np231. I'm thinking I might take this route first, because it seems the least expensive.

 

Check motor and trans. mount.

 

I'm pretty sure the motor mounts are good but I'll check them. How do I check trans mounts?

 

Trans mount sits dead center almost on betwwen the trans and crossmember. If you look at your crossmember you will see 4 bolt holes in the middle. That's where it mounts to the crossmember.

 

I went through this very same issue about 2 months ago.........
Went ahead and replaced the t-mount and then I saw the motor mount on the passenger side....there was over a 1/2" gap between the rubber and the metal surounding it......YEP!!!!! <-----that there was the problem!!!!
These fellers here recommended that I look there and once I was done...
BINGO!!!!! no more clunk!

 

does it keep clunking as your moving? or just clunk a few times at take off? mine clunked at take off then stopped. it was the rear diff. last time i changed the fluild, when i had that stupid leaking rubber plug on it, i put the new cover with threaded plug on and forgot to clean it out with brake fluild, and put walmart diff. oil in it. then it started clunking after a couple of weeks. so i took it off again, drained it and brake cleanered it, sealed it up and put royal purple diff. oil in and no more clunk. this was last year and still no clunking. i was just thinking, maybe i didnt put enough walmart diff. fluild in it the first time.not sure too far back to remember. lol

 

When I'm under load going up a hill in 4-Lo it keeps clunking when I'm moving, but when I'm on the road it's one clunk on takeoff when I hit the gas pretty hard. I'm also starting to get some weird slow-speed vibrations that feel like they're coming from the drive line, but I drove it 215 miles today without a problem.

 

Check your motor mounts and if all is well give your rear DS a good hard shake at the front and rear U-joints. Guarantee you're heading in the right direction. It will be a mount or U-joint.

 

I think I tracked it down. The drivers side motor mount is real bad, I'll be replacing it soon and we'll see if it clears it up. Any good writeups on this? It seems like it's gonna be a b!tch to replace because I have to work around the manifold and stuff...

 

What was the outcome of this? I'm having the exact same issue. Was it the engine mount? Did replacing the mount fix your problem?

 

Check YOUR motor mounts and trans mount. That's the only way to fix YOUR Jeep. Common problem. The mounts sag and the exhaust pipe hits on the crossmember. Your time would be better spent under the Jeep at this point.

 

Haha. Good advice. Yes I will do this but it's raining today so it's easier to stuff around on Jeep forums instead where I won't get wet.

Initially I thought it might have been the uni joints or front drive-shaft but they looked OK when I was under the Jeep. I wasn't sure what to look at next so thought I'd get online for some ideas. I was surprised when I found an exact description of my problem (i.e.- clunking when going uphill in 4-Lo and a single clunk on the road under hard acceleration).

What's the best way to check the engine mounts?

 

I actually checked the engine mounts recently by revving the engine and looking for excessive movement. I didn't notice anything out of the ordinary so I'm wondering if it's better to check them by jacking up the motor slightly...