Rear Axle Woes

[JohnC]

Some of you may recall that last fall I was concerned with a noise that appeared to be coming from either a wheel bearing or the rear axle. Well, I nursed it through the winter and finally bit the bullet and looked into it. Just by jacking it up and spinning things, I decided the pinion bearings were going. But, I decided to pull the cover and give it a look-see before handing it over to someone to fix. I could do it myself, but didn't have the facilities to do it the easy way or the time to do it the hard way. Trading money for convenience...

Anyhow, imagine my surprise when I found one of the spider gears trashed. And the other in apparently perfect condition!

Fortunately, I'd been sitting on a G80 carrier waiting for a good time to install it. This seemed like as good a time as any....

It's all done, and the forward pinion bearing turned out to be junk, as suspected. So, the damage was 1 spider gear, one pinion bearing, and a big hole in my wallet. On my side, the noise is gone and I now have a locker.

So, the shop, on their own initiative,added limited slip additive to the gear oil. I know it is not recommended, but is that because it's a waste, or is it going to trash my new rear end? Can I run it a couple thousand miles or should I get it out ASAP?

[DmaxMaverick]

I suggest removing the lube ASAP. The additives have corrosive properties the locker is not designed to handle. Previous limited slip models were designed to be friendly with these additives. Short term, there will probably be no damage, but since you are essentially in a break-in, I would not suggest leaving it in any longer than necessary.

[JohnC]

Epilog:


Tough Guy gets the award for best diagnosis. he said something like "the noises you describe sound like the ones my axle (also a 9.5") made just before it grenaded"

Here is a photo of the forward pinion bearing race:
http://members.aol.com/gmc65td/race.jpg

And the cone:
http://members.aol.com/gmc65td/cone.jpg

and the big surprise, a shot of the bad spider gear:
http://members.aol.com/gmc65td/spidergear.jpg

[rjschoolcraft]

The compressive fatigue failure that you have experienced on the gear teeth is the result of improper set-up at the factory. The side gears were not properly shimmed to center the contact pattern. The contact is too far to the heel of the tooth, concentrating the load in a small area. This failure is of subsurface origin.

The pitting fatigue on the pinion bearing is of surface origin as the result of debris from the gear passing through the contact zone.

FYI, the second shot there is of the cone, roller and cage assembly. The cone is the inner ring of the bearing. The first shot is of the cup, or outer ring. Each ring has a raceway surface for the rollers to contact.

I've seen many differentials and manual transmissions that were improperly shimmed from the factory. It's ridiculous.

[JohnC]

Originally posted by ronniejoe:
FYI, the second shot there is of the cone, roller and cage assembly. The cone is the inner ring of the bearing. The first shot is of the cup, or outer ring. Each ring has a raceway surface for the rollers to contact.Hydroscopic oil galleys, Batman! ;)


I've seen many differentials and manual transmissions that were improperly shimmed from the factory. It's ridiculous. Yeah, I was pretty peeved that I had to spend that much money at only 136K miles. I had it open aboutt 30K back and it looked fine. Interestingly, enough, the other gear is undamaged. I'll have to take it apart and get a look at the shims for grins. I installed a G80 carrier with unknown miles I got from a guy on e-bay. Hope it works out better!

[JohnC]

RJ-

Any thoughts as to why one gear would fail so catastrophically (damage to every tooth) and it's twin would appear unscathed?

[rjschoolcraft]

There are a number of reasons why this can happen.

There is considerable variability in material, especially with the material specifications used by the automotive industry (as compared to the aerospace world I've spent most of my career in). Statistically, the failed gear may have been toward the bottom end of the strength range while the mate was at the upper end. This can happen because of heat treat variation as well as the cleanliness of the material.

Even though the computed contact stress is the same in both members, the smaller member will usually fail first. This, too, is a statistical phenomenon.

Had this differential continued to operate, the mating gear teeth would eventually fail because of the poor load distribution that results from the failure on the other gear. The final result would have been tooth breakage and complete loss of power transmission.

[Hansh]

I had a similar differentail bearing failure at 70,000 miles on my 1999 Jeep Grand Cherokee. I caught it before it completely blew up. I could not believe it!

[rjschoolcraft]

HH,

Where in SE Wisconsin are you?

My in-laws live near Whitewater. Wife's brother lives in Menomonee Falls.

[markrinker]

Originally posted by ronniejoe:


Even though the computed contact stress is the same in both members, the smaller member will usually fail first. This, too, is a statistical phenomenon.

My smaller member has never failed under contact stress. Its statistically phenominal :D

[rjschoolcraft]

:D

I guess I should have seen that coming.

[JohnC]

Dang! I could have had this!

super axle (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33731&item=2451878780&rd=1&ssPageName=WD1V)

[rjschoolcraft]

Check out my post in the Members Forum:

http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=10;t=003702

[CareyWeber]

Originally posted by JohnC:
Dang! I could have had this!

super axle (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33731&item=2451878780&rd=1&ssPageName=WD1V) John,

Could you email me.

carey dot weber at us dot army dot mil

Carey