Blowing pinion bearings (two diffs)

WTF? Roomie blew his pinion bearing on his 8.25 last week. Took that as an opportunity to upgrade to an 8.8. Got about 200km on it and blew up the pinion bearing on it as well.
WTF is causing this? Diff isn't pointed at the sky so oil delivery should be acceptable, but I can't think of anything else that would cause this problem twice in a week.
Idea's?

(96xj, 4.0L, AX15, 3.55 gears, open diff, 33" shoes, ~4" lift)

How long was he running the 8.25 before it blew? And what do you by blow? Make noise or flat out destroyed? Has it been torn down and inspected? Any recent changes to it? What kind of driving was the 200km? I've thought I had a bad rear axle because I had a new driveshaft, the driveshaft was actually the problem. Ring gears normally throw a lot of oil, I wouldn't think a bearing could be trashed in 200km unless the fluid was bad or really low.

8.25 came from another Jeep. No idea on the miles, but I inspected it and verified numbers before it went in about a year ago and it was fine. Lots of wheeling since then. Last week he was just on his way to work and started feeling some real bad vibes. Got under and pinion could be shaken around a bunch. Tonnes of lateral play.
8.8 I barely inspected. He just picked it up at a wrecker, I checked pinion preload and verified all the bearings felt good. Threw it in and it was fine for about a week. Was fine last night, drove to work today and same deal. Started vibrating and making a bunch of noise. I haven't seen it yet, but he got under and gave the pinion a shake with me on the phone and I could hear it . Bearings definitely blown out completely. Apparently was smoking a bit.

I just can't think of what the common denominator would be, that could cause this twice. Yea, if DS was way too long and he compressed too far... But generally the u-joints blow out long before a pinion bearing. Twice in a row is too weird.

I also have to re-do the oil pan gasket and rear main in the girls XJ today (last night's attempt didn't go well and the rear lip must have slipped and is now pissing oil... ps. I hate 96+ XJ's).

Out of balance driveshaft? Pinion angle suck?

If the drive shaft jams into the pinion it can crush the crush sleeve and the pinion just kind of flops around it there. Is your 8.8 the type with the crush sleeve or the shims?

Or if he is prone to hot rod starts, using RPM's instead of gearing to go over immovable objects, he could over torque the crush sleeve (or axle wrap) with the same results. The pinon does weird things (weird angles) and the crush sleeve collapses, the pinion flops around until it self destructs. Worst case is if the pinion jams in the ring gear.

I'v done both on one of my trucks that was setup as a freeway flier. I'd run that truck at around 140 MPH on the Autobahn, Mr. Mercedes please merge right so I can pass .

With those 33's on there you are effectively starting out in second gear, not first. Just a guess, but those 33's are acting just like an overdrive of around 15%.

I ran a fourth gear overdrive (+7%) on a 2.93 rear end (around +12%), for pure top end speed. My crush sleeves screwed up periodically. I don't know exactly how or why, but it was pretty obvious it was a result of too high gearing and excess torque. Probably coupled with some rear end squat and odd drive train angles on occasion whne starting out or accelerating. The forces generated are rotational as well as straight line and eventually a 90 degree right angle. I can visualize the pinion generating some weird forces if it is stressed enough.

Just an idea.

8Mud said:

If the drive shaft jams into the pinion it can crush the crush sleeve and the pinion just kind of flops around it there. Is your 8.8 the type with the crush sleeve or the shims?

Or if he is prone to hot rod starts, using RPM's instead of gearing to go over immovable objects, he could over torque the crush sleeve (or axle wrap) with the same results. The pinon does weird things (weird angles) and the crush sleeve collapses, the pinion flops around until it self destructs. Worst case is if the pinion jams in the ring gear.

I'v done both on one of my trucks that was setup as a freeway flier. I'd run that truck at around 140 MPH on the Autobahn, Mr. Mercedes please merge right so I can pass .

With those 33's on there you are effectively starting out in second gear, not first. Just a guess, but those 33's are acting just like an overdrive of around 15%.

I ran a fourth gear overdrive (+7%) on a 2.93 rear end (around +12%), for pure top end speed. My crush sleeves screwed up periodically. I don't know exactly how or why, but it was pretty obvious it was a result of too high gearing and excess torque. Probably coupled with some rear end squat and odd drive train angles on occasion whne starting out or accelerating. The forces generated are rotational as well as straight line and eventually a 90 degree right angle. I can visualize the pinion generating some weird forces if it is stressed enough.

Just an idea.

Click to expand...

This. I suspect his ds may be too long. Looking into it now. Just got the case open.

Angle is dead straight with the ds.

Ha! Cross pin bolt broke off as well. This is fun!

Something doesn't look quite right here



This is the 8.8 pinion. Removal required a liberal application of Jeep hammer. Inner bearing was well lubricated and in mint condition. Outer was bone dry and welded to itself and the pinion shaft. The outer seal was about 5 seconds away from catching on fire when he finally pulled over (tonnes of smoke) and once we got the seal removed, it looked like it'd been on fire for a while.
As the inner bearing, ring and pinion, spiders and carrier bearings were all good, I suspect he just didn't have enough oil to fill up the pinion galley. I don't recall how other diffs accomplish oil delivery to the outer bearing, but this one relies on filling the entire space between inner and outer bearings, so the oil seeps UP to the outer bearing, then past and out through the front galley. Seems silly to me as oil will always slowly seep out from the inner bearing, so even moderately low oil will cause the outer to grenade.

At any rate, that answers the question for the 8.8, but keep in mind he put the 8.8 in because he blew out the same outer on the 8.25. At this point, I think they're different issues. 8.25 probably blew out because the DS smashed the pinion in on bottoming out and squashed the crush sleeve, so the pinion could just flop around. Then the 8.8 may have suffered the same fate for the same reason if he'd wheeled it, but instead the low oil got him first.

What I don't get though is the 8.25. The DS was the stock unit, and he lifted the Jeep 4". That should've given him MORE DS clearance, not less. Looking at the front of the DS (slip yoke), it does look like it'd been bottomed out a few times. All I can think is that his 4" leafs located the axle forward an inch or so, but haven't had time to measure.

Just waiting on a used gear set for the 8.8 now. This is his DD so we need it back on the road yesterday. Have a spare d35 in a pinch, but hopefully we'll find a used 3.55 (to match current front) or a 4.10 (to match one of my spare d30 sets I can install).

*edit* Oh yeah! Not pictured is the pinion splines that are twisted about 2mm around. This axle had a hard life me-thinks.

Great update. If that much hear was generated I'd check the housing real good for damage. 8.25 doesn't have any oil slingers to slow the flow of oil up to the outer pinion, not sure what the 8.8 has. I measured fluid height stock before I rolled the pinion up on mine and fill it to the same level as an added safety. Basically the outer bearing sits in about 1/8-3/16" gear oil iirc. Not that much.