We were going in to change the rear brake pads on my ‘00 D2 and found a narrow band of axle oil on one of the driver’s side pads. Oil didn’t seem to be visible anywhere else.

I checked a few threads, and it seems that axle leaks can be due to three things: bad hub, bad axle seal or bad o-ring. (Let me know if this is incorrect.)

Do you need to go in and take it apart to figure out which it is? Or does the fact that the oil is on a brake pad give an indication as to what the source of the leak is? (I’d rather buy the part first, if possible, and do the job once, rather than twice, once to diagnose and a second time to replace the offending part.)

Also: is it generally a good idea to replace the axle nut when doing any of these repairs?

 

Agree. Assuming it's NOT brake fluid....and it is gear oil. Doing this twice would be a waste of time. So I guess you can;t just leave it up on blocks until you get the part? If the O ring is bad, it's like 8$. If the hub is bad internally, then it's about 90$ for the Britpart (which comes with the speed sensor and O ring). So you are going to need a 4ft breaker bar (3/4" drive) and the right socket. i think it's a 32mm, deep well.

You can't really repair the hub internally. do you have the RAVE downloaded yet? It gives the specifics for this repair including the impressive 300+ ft/lbs torque for the axle nut. I used aftermarket new axle nuts (i forget where I bought them), but I was not impressed as they are different than the OEM version. There is a link somewhere on this site.... or search "download RAVE discovery 2" on google.....There are a few vids on youtube as well.....

 

I kinda doubt the o-ring would just start leaking, more likely the rear hub wore out and the seal is not able to seal anymore. Were 3 amigos on? Usually that is pre-cursor.

 

OK, some clarification. On the rear axle, the o-ring is the axle seal, so those are not two separate possible issues. However, further research suggests that a problem with the breather tube can cause the o-ring to leak.

The fluid is oily and black. I replaced the diff oil last week after six years, so it is most likely that on the brake pad and not brake fluid or grease from inside the hub. I thought this meant that it must be a problem with the o-ring, but if (per Extinct) a worn hub can cause the o-ring to stop doing its job, then I have to take that into account. I've had three amigos on and off for decades, so it's hard to tell if that points to the hub or not (though it would be great if replacing the hub solved that problem too). I guess I'll just have to order all the parts and return any that I don't end up using.

Regarding the hub brand to go with: I've generally found Lucky 8 parts to be reliable, and theirs is half the price of the ones at AB and Rovers North. Does anyone have experience suggesting not to go with the less expensive one?

I have downloaded the RAVE. I will go with the OEM axle nut. My mechanic friend has a four-bay shop in his backyard with a lift, and I can't take up space on his lift for a week. Pound for pound he is the strongest person I've ever met, so I think he'll be able to handle the torque requirements.

 

The o-ring is a static seal, meaning it does not move. It just seals the od of the hub to the axle housing. They do not wear out. Yes, a blocked breather tube could cause pressure in the axle to build up due to heat and force oil past the o-ring. That would be indicated by dripping only when hot and driving, not sitting in the driveway cold. If you remove the wheel and the brake disc you should be able to tell if it is coming from between the axle and the hub or the hub and the housing. Both require removing the hub.

The hub nut is too tight for the strongest normal sized human. I cracked a husky 1/2 drive socket and then snapped a Kobalt 1/2 drive torque wrench removing them before I bought my 3/4" drive set. It is quite literally 3ft cheater pipe with 200lb man on it to loosen.

I have found no difference in ebay hub quality vs OEM, although some here have.

 

It did turn out to be a bad hub. Replacing it stopped the leak, eliminated some vibrations that I had thought were in the drive train, and hopefully will prevent the return of the three amigos for a while. It’s a very quiet truck now.

My mechanic friend was pleased that the repair was relatively easy compared to the many others we have done. He did manage to get the axle nut off using a half inch drive + extension + cheater bar.

He thought the axle nut could be reused, but since I had bought a new OEM one ($26 at the dealer), we went with that.

Thanks to everyone for their advice.