[4.0H.O.XJ]

Chrysler 8.25 29 spline (verified) 3:07 open rear diff in a 1996 XJ on "31 tires. Hack 'n tap SYE.

I am getting a steady hum at low speed (sounds the same as large tires on pavement) and it gets louder the faster I drive. Same noise, but faster, and louder. There is a "sweet spot" at about 45 MPH where it quiets down just a little.

It is only coming from the BACK. I have changed both outer wheel bearings and seals and re-filled with synthetic 85w-90 gear lube, no change. Makes the same noise with clutch in or out, engine off or on when moving. CEASES at 5 miles an hour.

I originally assumed it was road/tire noise, but the noise only started recently and is only coming from the BACK.

I went under the Jeep tonight after a highway run, and the pinion area of the rear diff where the driveshaft yoke splines into it was warm to the touch..... Not hot, but noticably warm. Drive shaft and U joints are new. Pinion angle looks OK to me. Driveshaft is a front D/S from a 96 XJ modded to fit the rear with H 'n T SYE. Everything is lubed and greased. Cant figure it out, but alll fingers point to pinion bearing.....maybe.

ANY IDEAS OR ADVICE? Pinion bearing? what the......??? Never seen or heard anything like this before.

Thanks.

[4.0H.O.XJ]

Here's a pic or two of the driveline angle. Anyone see any issues with this or why it's making noise now?





I double checked U joint straps, Yoke connections front and rear, gear lube and d/s travel.....and it makes no noise when jacked up and spinning tires freely by hand. The only test I HAVE NOT done yet is to physically run it in gear to listen for noises.

thanks.

(*** Sharp eyes will notice that the slider looks too short, but it is fine and is nowhere close to disco'ing even under full droop/flex.)

[99WhiteXJ]

When my pinion bearing went out in my old D35 it made a high pitched whining noise like when you're in an airplane as well as a "growling" noise and similar to the tire hum like yours. It also got louder relative to speed like you described. There was a lot of play in the yoke also. If you haven't checked for that, it may help narrow down the problem. Not sure how much play you should have with your setup, mine was stock when it went bad.

[bebout]

If it's not the pinion it could possibly be the carrier bearings.

[sprintagogo]

Try borrowing a set of stock road tires and driving on them. I had a rumble that seemed to be getting progresively worse and I couldn't pinpoint the source. I suspected that eventually it would get real bad or something would break then I would know what it was. Over time I changed things around a bit, swapped a few different axles and came to the conclusion it must be in the transfer box. One day I had to swap to a set of almost bald road tires from a Jeep I was breaking while my knobblies were away being revalved and balanced. Surprise, surprise, rumbling completely dissappeared. The tires were BFG MT's and I have had them from new so I suspect that as they wear the tread block surfaces must lose their curvature and become flat, hence the rumbling.

Other than that it could be connected to your rear pinion angle. Have you physically checked the angle with an angle finder or can you snap a side-on pic that shows the driveshaft and the diff nose?

[ShaneO]

I have the same thing going on and now I'm starting to get a little concerned - is this thing going to strand me? What other damage is manifesting in the background etc etc. I'd love to see a link to the pinion bearing fix.