Rear axle bearing postmortem

[bloc]

Some of you may have been watching my process to track down a rumble/whine/bearing noise over the past few months. That thread is here: New driveline noise after lift - https://forum.ih8mud.com/threads/new-driveline-noise-after-lift.1228472/

Turns out it was a rear axle bearing, which is something I suspect will become more common in the future. According to @cruiseroutfit these aren't exactly rare these days, and as we accrue more and more mileage the odds are this will be popping up more often. I'm even considering doing the other side even though chassis ears seem to suggest it's in good shape.. but I already have the tools so I might just knock it out.

Anyway after I got it out I figured it would be interesting to take it apart and post pictures. Seems like an odd situation to have only one ball bearing bad, and I was kindof hoping some of you smart people possibly with materials experience could help us all tell what happened. Also I have no clue whether the other bearings going bad will fail in the same way.. but it's all info. Ie, I think it'll help.

This will be picture heavy. Please if you have something to add, speak up. I still have all the parts on the bench so I can get other angles or whatever if needed.

The first time I pulled the bearing assembly I noticed some brown goo between the bearing itself and the seal that rides on the axle shaft and keeps diff gear oil out of it. I considered this a bad sign.

On the ground the backing plate would rumble when rotated around the axle shaft. With snowmageddon approaching, I put it all back together so I had something 4x4, and ordered parts.

 

[bloc]

So I got the parts and pulled the assembly to change the bearing. That went well. I then cleaned up the old stuff as well as I could to get some pictures.

When looking closely, I noticed chunks of metal stuck to the back of the inner bearing shield. It is magnetized in lines and they pass by the tip of the ABS sensor on that corner to give the ABS computer a wheel speed signal. This is that bearing shield, with metal stuck to it, after cleaning with gasoline.

The outer bearing race is a large assembly, with two sets of ball-bearings pulled against each other. I found it interesting that the shell material was hard enough to serve this purpose, expecting there to be races pressed in, but that's not how it was built. On mine the inner of these two races was fragged, all grease brown and nasty, chunks of metal.. but the outer race was basically perfect. Grease still white and more viscous, no apparent mechanical damage. The bearing cages act as seals against the inner diameter of the shoulder between the races and it seems they do their job to avoid cross contamination.

These pictures should show the layout of that shell, and the damaged and clean race.

This one shows the damage, right next to the same race in good shape. The damaged portion was at the top, or the part that would see the weight of the vehicle on that side.

This is the good race on the other side of the bearing shell. Not absolutely flawless, but easily good for many more miles. But, it is attached to the bad part.

 

[bloc]

On the bad side, I expected to find a bunch of trashed ball bearings. Curiously, only one was fragged. The others had very slight damage, most likely incidental to the bad guy self destructing and leaving pieces of itself all over the place.

This is the bad one.

 

[bloc]

Also interesting to me was the fact that all of the balls on the bad side appeared to be stained. I got some pictures of the notable difference in finish. Looking close it didn't seem to me that this was merely mechanical damage, but almost like the darker grease on that side had stained them in some way.

As I said, the other balls in the bad race had light damage, but it was hard to get on camera. Still interesting to me one ball going bad didn't damage any more very severely.. but this is what came out.

Note that I didn't do an amazing job of cleaning these, so some of what might look like damage is simply grease or swarf stuck to them

Full race, bad one on top.

 

[mcgaskins]

How many miles were on the 200 before you started hearing the noise?

 

[bloc]

The inner race on the bad side was clearly damaged but not horribly so. Far cry from the outer race.. and this makes sense, given the same half or less of the outer race sees the same force (weight of the vehicle) where the inner race is constantly rotating and distributing the forces.

Bad inner

Good/outside inner

Also snapped some pics of the assembly together as installed.

Bad side removed so you can see the cage/divider

 

[bloc]

How many miles were on the 200 before you started hearing the noise?

Roughly 155k. I think it may have been building for a while, but swapping in suspension with spherical ends transmitted more of the noise into the cabin, causing me to correlate it with the added lift, and throw me off the trail.

I put almost 7k on it after clearly noticing it, before tracking it down and changing the bearing. In my case it was not a quick failure. OTOH I don't have mud terrains which I feel would mask a lot of the noise.

All of that troubleshooting stuff is in the above linked thread, including audio of what the different corners sounded like through chassis ears.

Edit: still not sure why it failed. I got the vehicle at 105k from a dealer, PO lived in Tennessee. The condition of the hitch receiver suggests they did some towing with it, so possibly a travel trailer or boat. Not sure though.

Edit2: some people only find this when they get an ABS light on the dash, because the bearing swarf and movement destroys the tip of the ABS sensor. Mine only had light marks on the sensor, though it clearly wasn't in like-new shape. My failure method may have been different than other people though.

 

[rlynch356]

how off is your pinion angle? seems like your are running a fair amount of lift.. Or the bearing seized (the one you show scared anyway.. the discoloration is from heat BTW..

 

[bloc]

how off is your pinion angle? seems like your are running a fair amount of lift.. Or the bearing seized (the one you show scared anyway.. the discoloration is from heat BTW..

Rear axle is near stock height, so I'd assume pinion angle is just fine. Heat occurred to me for the ball discoloration, but it seems like the races would show some of that too, and they don't.

 

[Climbingnut]

That brown gunk looks like either water made it’s way into some dark grease or some diff oil made its way into some white grease. Either way, that’s a mixing of two liquids that shouldn’t be mixed. If I was in your shoes, I’d do the other side while you have everything out. With 155k on it, it’s just good PM to do both sides at the same time.

 

[bloc]

That brown gunk looks like either water made it’s way into some dark grease or some diff oil made its way into some white grease. Either way, that’s a mixing of two liquids that shouldn’t be mixed. If I was in your shoes, I’d do the other side while you have everything out. With 155k on it, it’s just good PM to do both sides at the same time.

Based on the new bearing and the good side of this one, the factory grease is white. So some gear oil mixing is plausible.. maybe the inboard race getting fragged released some of the preload between the bearings and allowed the assembly to walk around some, impacting function of the axle seal?

I kindof defaulted to it being a result of water intrusion and rust, but you make a good point.

This also reminds me I wanted to check the abs sensor on the other side for brown goo, in spite of it sounding good with chassis ears. Will do that soon.

 

[bloc]

Other side ABS sensor.

I’ll be ordering another bearing and throwing it in in the next few months, and tearing it down too to see if it must be in bad shape to allow the brown stuff.