Hello, so I have been having a problem with my 98 XJ. So occasionally when I take off from a dead stop on medium to hard acceleration there is a grinding noise that sounds like it's coming from directly below me. It's a 4.0 with an AW4 and NP231 tcase. 202k miles. It does not do it on a grandma take off or if I slam the gas when already moving. It's also very inconsistent. It will do it at one red light but not the next. ??? I have already searched but haven't found my exact problem. I recently changed the transmission mount. Tcase fluid is at level. Needs changed and I will do that next weekend but it's at the correct level. This is in 2wd. Haven't tried in 4wd. Any advice would be appreciated. It only grinds on acceleration and not when moving.

 

Have you tried removing the front driveshaft ? I would be curious if you notice any difference. Front bearing in that 231J could be wearing out also.

 

See if your exhaust pipe is touching the crossmember here.

 

Ok, so no I have not taken the front driveshaft off.(might try this weekend)
My exhaust pipe is not touching the crossmember.

 

Bad u joint in rear driveshaft?

 

Mine is making this noise as well. I can feel it through the shifter when it does it. Only does it on take off and stops after I've reached 10-15 or so. Almost sounds like a muffled boiling sound. (If that makes sense.)

 

I think mine sounds a little more metallic. I tried getting a recording today but that didn't go to well. My shifters(auto and tcase) both vibrate a ton when in park with the engine idling. Could shot engine mounts do this and the grinding noise?

 

It sounds like the motor mounts and trans mount are all in need of replacement. It can both cause the shaking and allow the engine to shift enough on take off to push the exhaust into the cross member. I am in the process of fixing the exact problem just waiting on parts. It may look like the exhaust is too far away but you would be suprised how much it moves.

If you go down a rough road kinda fast does it bang? Going up gravel hills on power with axle hop does it bang?

 

I just replaced the trans mount. Do you guys think this is a turn up the radio situation or fix now before you break something situation. I'll replace the motor mounts when I get a little money. I can't find anything that's out of place. The rear driveshaft U-joints are fine. The one at the front driveshaft to transfer case has a little play. Very little.

 

I would do a thorough inspection of the motor mounts, specifically the drivers side. Probably a good idea to remove the airbox. Check for obvious cracks in the mount. I would also drive it and cause the noise then immediately in inspect the key contact areas if it was a motor mount. The fan hitting the road and the exhaust on the cross member for witness marks. If you don't see any witness marks or a cracked motor mount I would be concerned it is something in and important part of the drive train. Its always best to locate the noise before making a decision about whether to drive with the problem or not.

 

I didn't see any bad cracks in the motor mounts. There is no signs of anything rubbing.

 

My friends does this and you can feel it, we've come to the conclusion that his tranny is screwed up

 

But wouldn't a screwed up tranny do that every time. Also it's working fine so how would it be screwed up? I'm not seeing any damage so I'm gonna keep driving it. It's my DD and I can't afford to have it looked at or out of working order.

 

Mine has had this noise since I got it last year. I drive it everyday with no issues. I haven't been able to find the source as of yet. But driving it everyday it doesn't get worse and it doesn't do it all the time either. I thought something was up with the tranny at first also but after almost a year it seems not to be the case. Maybe if you can upload a video or audio clip of the noise it would help decipher what it actually is.

 

I have tried recording it. Too much wind noise. I bet that looked good to my neighbors, me flooring the gas while holding my phone outside. I noticed it was colder today that's it's been and the sound wasent as loud or not there at all.