Nasty grinding/vibration when accelerating

2001 XJ, 4.0L, 4wd auto, 231 t-case, D30/Chry 8.25
3" rusty's lift, 31" BFG AT's, rusty's t-case crossmember w/ 1" drop

This problem has been getting progressively worse for several weeks now. It started happening very mildly, and is now getting much worse.

It happens when I accelerate only. It doesn't happen above ~35mph. It will grind in both 1st and 2nd gear, but mostly 1st. If I accelerate VERY gently, it will sometime not do it. It happens in 2wd or 4wd, high and low range. Since it's been getting worse, it will happen when I'm stopping as well, and even somewhat continue once I come to a stop. ???

I thought it was the x-fer case because of the way it was grinding, so I swapped another one in, and it didn't change anything. I have taken the front driveshaft off, same thing, maybe even worse. I dropped the tranny pan and changed filter/fluid, nothing changed.

I have researched and found that I need to check/replace u-joints, and check the slip yoke. Is there anything else I should check? Is it possible that it could be the torque converter? I wouldn't think the tranny since it will happen in multiple gears, but I guess anything is possible...

Thanks in advance for your help.

have you checked the u-joints on the rear shaft ?

No, but when I took it off to change the t-case I didn't notice anything bad on it. I'm sure they need to be changed anyway, but wouldn't I notice somethig bad when taking it off?

Since it's been getting worse, it will happen when I'm stopping as well, and even somewhat continue once I come to a stop. ???

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Drive/flex plate bolts

For what it's worth, I've been having the exact same problem for the past two weeks. I'm hoping its the rear driveline since I'm getting ready to put in a lift and I'm going to replace the rear drive shaft and install a SYE at the same time... Either way it's past due since I'm on stock suspension, stock u-joints @117K miles. I dont want to end up dragging a driveshaft down the freeway. If new u-joints fix the problem then please post it on here...It's likely the same problem I'm having.

My rig is also an '01 auto, np231 w/8.25 in rear. Initially the vibration/grinding happened when I accelerate hard, but not if I start off softly. Sometimes if turning a corner while accelerating it happens more violently. I'll get the new driveshaft in a week or two and see if it goes away. Prolly otta change the joints in front as well.

Good luck.

Thanks to all.

Please keep me updated spacmun. I'm going to check into my torque converter / flexplate area and I'll post an update as well.

Andrew T said:

No, but when I took it off to change the t-case I didn't notice anything bad on it. I'm sure they need to be changed anyway, but wouldn't I notice somethig bad when taking it off?

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not by just looking at them. Lift the back wheels off the ground, grab the shaft and feel for any play. If the shaft is off, turn the caps with your hands and rotate the U-joint, you will know if it's bad. Or pull the caps off (careful not to drop all the little bearing on the ground) and inspect.

U-joints are easy and cheap to replace anyway.

could be Drive/flex plate bolts like langer1 said.

I just remembered that I never followed-up here. For what it's worth, my noise/vibration is gone. I've installed the RE 4.5" lift with a Teraflex SYE and new CV driveshaft. Went with Bilstein 5150 shocks and it drives much tighter...I wonder if the decreased travel when I take off did it, or more likely the driveshaft. I've got new joints all around now, so maybe that helps as well. Anyway, I've got other vibrations to deal with now (driveline, but minimal) so at least I've got something else to gripe about. :smsoap:

I'm not one for bumping old threads, but my mother just picked up a '95 XJ that is experiencing similar issues. Her rig is stock. I drove it tonight and noticed that it would happen accelerating fairly hard, and when I tried gently backing up my driveway which had about 3" of snow. I'll look at it tomorrow, but I was wondering if there were any suggestions about this. Thanks.

sounds to me like your getting major axle wrap and the top yoke on the rear driveshaft is binding..

I had the same problem and it was the centering yoke of the double cardian u joint setup on the front drive shaft.

If you have a LSD, then it is probably that that is rumbling, usually on take off, more so if you are at an angle, Needs a new clutch pack

Thanks all for the help!

bajacalal said:

I had the same problem and it was the centering yoke of the double cardian u joint setup on the front drive shaft.

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bajacalal could b right however i had the same problem and was going though u joints like candy. whenever you change ur u joint always check what u are attaching it too the yoke on my rear diff was worn on one little corner this made the drive shaft apear tight however under torque causes separation from the strap making everything out of center. thats why its only when u accelerate that it vibrates and when u lay off the throttle it gets better. to the originator of this post it will not get better with a lift or new u joints. those things just disquise the problem for a while.

thats my 2 cents i went though 4 u joints before acually taking the rear yoke off and inspecting it on a bench. when u think about it its 4 bolts and a nut and the yoke is out. might be worth a look when that u joint goes out on ya on next time ur on the trail