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Rear differential noises


NAXJA Forum User
Lansing, MI
Ouch - I just wrote out a few pages about this problem I'm having - I guess next time I'll learn how to use notepad, huh? Alright, here we go again:

I've got a '99 XJ 4 liter, NP231, all stock. Right now I'm trying to track down a rear differential noise I'm having, but I thought I'd ask some knowledeable XJ people before I dug into it too far.

The noise occurs when I'm on the throttle lightly at highway speeds. It's coming from the rear of my Jeep, so I think it's coming from the rear diff. I already took a look at my transfer case, but I don't see anything wrong with it. When I replaced the chain in my transfer case a few months ago, I visually inspected the bearings, and the synchro/blocker ring in the transfer case. I didn't see anything out of the ordinary, and all the parts were in good condition. So, I'm led to think the rear differential is making noise.

I haven't measured anything in the rear diff, but last time changing the diff fluid I noticed that the wear pattern on the ring gear was on the outer edge of the gear. I don't know whether this is a common occurance on these differentials or not, so I thought I'd ask.

I also found a Differential overhaul kit at http://www.tellico4x4.com/axle/installax.htm but I don't know whether or not this kit comes complete with shims for the pinion gear. I also don't know what differential is in my XJ. I think it's the Dana 35, but I'm not positive - how do I find out?

Does anyone have any other idea on what may be wrong?

what do you have in the rear? which diff? which spring pack (stock? stock +AAL? stock +shackle? stock +block? aftermarket pack?) and how much height?

What you describe sounds like results of axle wrap to me.... when you accelarate the axle gets rotated on the spring and angles get messed up....

btw D35 is kind of rounded while the 8.25 is more hexagonal.... and has a weird lip on the cover....

also, IIRC if you have ABS you have the D35
Sorry, I should have been more specific. My XJ is completely stock.

I would agree on that issue, but on normal acceleration the rear differential doesn't make any noise. I don't think that's the issue.

My XJ does not have ABS.

pop the cover and see how the oil looks like :) Also are there any dings in the shaft? also the slip yoke.... how does it feel? tight? or wobbles side to side....

In regards to noise it can change with load and other noises might cancel it out as well.... so the fact that you don't hear it at times doesn't mean it's not there....

I don't offroad with the jeep (yet :) ) so there are no dings in the shaft. I visually inspected it a month ago, and have had this noise for more than that.

The noise hasn't changed, and I don't know how it developed. I just started hearing it one day. It hasn't gotten any worse, though, so I'm pretty stumped as to what it is exactly.

The oil in the diff has about 500 miles in it, I just replaced it. The oil I replaced that oil with with looked fine, too (I replaced that about 20,000 miles ago) - there hasn't been anything metal or gritty in the oil. I use synchethic gear oil with a heavy weight (although I can't remember what I put in it, how awful is that) - even though I can't remember what it was, it wasn't cheap stuff, it was like 90W120 synthetic or something like that (what the users manual recommends for towing)

Any other ideas?
Did you fully inspect your drive shaft and eliminate it's u-joints as a cause?

Are all of your motor mounts in good shape (the driver's side mount does rip quite often -- include a tranny mount check)?

Under light throttle at highway speeds could indicate a bad set-up or a limited slip diff that's wearing oddly (like different air pressures in the rear tires or other mis-matched circumference issues)

If you suspect spring wrap (seems to me that light throttle at highway speed wouldn't get this for ya, but drivelines all behave a litle differently), compare the profile/shape of your rear leaf packs... look specifically at the area in front of the axle on the pasenger's side of the ride - is the arc there as smooth as the arc behind the axle and do BOTH springs look identical?

You should have a ChryCo 8.25 diff since you don't have ABS
When I replaced the chain I inspected the u-joints, and they were all in good condition. I didn't replace them, but they didn't wobble, have any noticeable play, or catch in any way. The slip yoke is tight, it doesn't wobble at all.

The motor and tranny mounts appear to be in good shape. I can move the transfer case a little bit if I lay on the ground and push upwards on it. It moves a little, but it's as firm as I expect a rubber mount to be.

My rear axle isn't an LSD. If it's supposed to be, maybe that's the problem :D

I've owned this XJ for 2.5 years, and as far as I can tell it was all stock, unmolested when I bought it. I'm the only one who's ever done any work on it (and yes, I do know how to work on vehicles)

I don't suspect spring wrap, but I also haven't specifically looked for it. As far as I can tell the leaf spring packs are symmetrical.