97 XJ Grinding/Thumping Noise

Cherokeekid88

Cherokeekid88

Well-Known Member
Joined
Jun 30, 2007
Location
High Point, NC
I hav enoticed in the past couple weeks, this grinding/thumping noise and I am driving down the road. If I let off the gas while moving at a higher speed (20mph+) its much more noticeable. If I put my feet on the floorboard while in motion, I can feel it. Can't tell though wether its from the front or rear....but my first guess is rear wheel bearings.......
Anyone have any ideas on what else it could be?

Front driveshaft is removed at the moment. Mostly everything up front is new(er), Transmission mount and engine mounts are less than a year old.
 
Jody Treadway said:
What are the specifics on your Jeep? Lifted, type of lift and height, etc.
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sorry. 4.5" IRO long arm kit. RE 3.5" leaf packs, 1" shackle and HD Offroad Engineering relocation brackets. 33x12.50x15 BFG's. IRO Tie rod, new TRE's, New Ball Joints, new upper control arm bushings. Brown Dog motor mounts, new tranny mount. rear axle is Chyrco 29 spline 8.25 with yukon 4.10 gears. front is stock d30.
 
Since applying and releasing the throttle changes the noise, you need to focus your attention on items that are effected by pinion angle change and driveline torque.

Do you have an SYE? What is your rear pinion angle set at? Any play in the rear axle yoke that would indicate wear in the pinion bearings? Rear drive shaft ujoints worn or dry?
 
Well let me rephrase that, Applying the gas or not, it doesn't really change....but I guess with no exhaust noise when my foot isnt on the gas, I can hear it better. No SYE, I do have a drop on my TC since the IRO kit allows you to have the corssmember dropped to compensate for such.
Not sure on pinion angle, I sused to know it but forgot...I know that I need to do an SYE because I get a slight vibe when giving it some much harder gas than normal.
I will check play in Rear DS after work.
 
Sounds to me like the rear u joint at the transfer case. Do you have a transfer case lowering kit? The ultimate fix and upgrade would be SYE but at least a transfer case lowering. It doesn't have to have slop to in the drive shaft, what happens is the angle is so tight at the T case it's binding up enough to make some and wear out a u joint.
Of course this just guessing from what your describing. Clanks, bangs and grinds just sound like a good running XJ to me lol. Never heard one that didn't have all kinds of sounds.
 
Im gonna try and check it out this weekend while I changing the brakes.
I do have an IRO long arm kit that allows you to drop the TC to avoid the SYE...I know I need to do it and will, just need to get this fixed asap...it seems over the last week it has gotten alot worse
 
I sold a jeep with a similar noise... I told the guy it might need a rear end, sounded like the pinion bearings going to me... then again it was only at certain speeds and come and go randomly.
 
Cherokeekid88 said:
guy at the shop says its my T case....needs chain replaced....
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oh this sounds very familiar. I swapped out my NP231, then with the XJ still on jackstands, I fired it up, but it in gear...noise still occurred, the consensus seems to be pinion bearings...http://www.nc4x4.com/forum/index.php?threads/rear-end-growl-when-decelerating.143482/
I still haven't changed anything in the rear end yet, so don't know for sure. I'm kicking myself for swapping out the t-case.
 
I have a 97 xj with 4.5 inches on it. Had the same symptoms and it turned out to be pinion angle. I had bought my kit used and it did not come with shims. I believe I put 5* shims under the ear leaves and replaces the rear drive shaft u joints and it fixed the grinding noise. Angles can make a huge difference. Check this for more info if you want to check it out. http://www.pirate4x4.com/tech/billavista/PR-shaft/index2.html
 
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