AlpMan

Hey guys,

I'm having a strange "groan" coming from what sounds like the rear of the Jeep. It's been around for a few years but getting progressively louder the last few weeks and gotten to a point where I feel needs to be fixed. It's a 95 XJ with the 4.0, auto trans (AW4), NP231 and the Chrysler 8.25. Stock height.

- Starts at about 5 mph and gets louder at about 30-35 and then quieter again at higher speeds
- The sound gets louder as I make a big swooping turns (both left and right)
- Pitch of the sound gets louder as I step on the gas. If I coast it gets quieter (but is still there)
- Sound still happens with either transfer case or transmission in neutral
- The sound is louder on warm days and quiets down when ambient temperatures are cooler
- The sound is consistent with the rotation speed of tires, so sounds like something in the drive-train after the transmission

What I have done:
- Replaced wheel bearings with no change in sound
- Replaced driveshaft U-Joints with no change in sound
- Opened Diff and inspected everything. Looked good, fluid was clean and replaced with heavier 80W-90 quality gear oil and zero change to the sound
- Replace drums, pads and all brake hardware
- Lifted rear of jeep and checked drive-train with stethoscope. Could not identify any rubbing, grinding or weird sounds
- Spun driveshaft by hand and everything is smooth and solid
- Checked transfer case fluid

Any thoughts? Hints on what to troubleshoot further? I am at a loss and don't know how to proceed without spending big money to replace things like the entire rear end, etc. Many thanks for any help!

awg

When you inspected the rear diff, did you use a dial gauge and/or marking compound to check gear tooth engagement & pattern ?

That would be very helpful to show if either pinion or side bearings are beyond spec

another thing to try is jack the rear and run it up thru the gears, tends to isolate bearing noises

country2

Sounds like a bearing,either pinion or diff bearings.

Dave51

Can you upload a video (soundtrack) of that? Most noises are described as "whines" as opposed to "groans", so maybe we not be thinking in the right direction.

Did you jack it up, run it and listen for the noises? Tie heavy duty rope to bumper so if it falls off while doing this it won't go too far.

Tires and rims OK? Check for out of round while tires are spinning.

OldTires

Sure does. This is from the FSM for my 1996, about the 8.25

s346k

unhook the driveshaft from the rear dif and see how much play is in the pinion. i’d guess that’s the culprit. bearing.

Dave51

To be clear, you replaced the REAR wheel bearings?

AlpMan

Just an update. I tore the diff apart this weekend and finally found what was going on. There was the ever so slightest sideways play with the entire carrier. It seems that somehow the carrier bearing cups unscrewed a little (even though the clips where still there) and so when I was going around a corner or giving it gas, the carrier was moving further away from the pinion gear and thus producing the sounds. All the bearings still seemed good, so I just tightened up the carrier bearing cups, adjusted the gears to the proper backlash and put it ll back together. As good as new! Thanks everyone for the help and suggestions.

OldTires

Thanks for the update, AlpMan. I definitely wanted to know what the issue was. Glad it wasn't bad.

Dave51

Thanks for the update! Please stay in touch. Did you have unusual tire wear with the noise? If you ever get one of those "4 Wheel Alignments", note what the rear wheel toe-in and setback is, or use the string method. With those clips it is impossible for the bearing adjusters to loosen up per se, but the casing is somewhat flexible (see procedure on carrier removal).