So a few days ago I noticed a bit of a whirring coming from my rear. I thought it might be the fuel pump or a small exhaust leak but, having just changed the front differential oil whilst replacing the axle seals the week previous, I decided to check the fluid in the rear. I popped out the plug and...

Ewww.

Black, gnarly old oil that tasted like burning came out. I immediately went about changing it all. Opened the back, got it drained out. Surprisingly, the gears all looked relatively pristine. Spun the axles, no problems except for a little chip in a part of it that isn't even a gear...

Wherein AJ attaches pictures to illustrate what he's talking about:





So I have no idea if this is even an issue, because honestly... for the life of me, I have never even given thought to my differentials. There weren't any chunks of metal anywhere in the diff, so I'm not sure what to make of this.

Any thoughts? What say ye??

 

I'd say eat less beans!

 

You'll probably be okay, if everything looks good and you don't notice any abnormal wear, stress cracks, or discoloration due to high heat build up.

Yeah, you have a chunk gone, but you say you didn't find any metal. Two possibilities...

1) The chunk got ground to powder over time, so you're not seeing it.

2) The chunk was missing prior to installation. It looks like you have some machining chatter marks near where that chunk is gone. Could be that it's been that way since it was assembled at the factory. Missed cast/milled or damaged during transport to the factory. Wouldn't be the first time a slightly damaged part was installed.

Clean it out good. Put some fresh oil in there and button her up.

 

Done and done. My whirring noise is still there, so I'm at a loss still. It usually hits when I'm doing 25 to 50 miles per hour and have my foot on the gas. If I take my foot off, the noise stops. I was thinking fuel pump or exhaust at first, but I can't reproduce the noise with the thing in Park or Neutral, so... I dunno. From what I know of it, if the bearings were going in the thing that noise would be there all the time. Maybe wheel bearings? But it doesn't seem to be coming from one side or the other. I got no play in my drive shaft at all, so I'm pretty sure it's not the pinion bearing.

 

And then I say to myself... "Carrier bearings?"

Hrmm. Damnit, and I need to drive like 190 miles... tonight. What happens if the carrier bearings crap out? Not that I think they would, because the noise only started a few days ago, but... I don't feel like drive-shaft pole vaulting across the New Jersey Turnpike tonight.

 

If you change your mind, don't forget to share. YouTube.

When I've had them fail, they whine, then growl, then grind/scrape, then thunk thunk thunk thunk...then all heck breaks loose. It isn't a quick process. You can hear it coming.

Is it just worn gear noise you are hearing? It isn't uncommon for older diffs to whir a bit and still run another 100K.

 

No worries... I've got a camera set up, just in case.

I hope it's just worn gear noise. I have no idea what worn gear noise sounds like. This noise isn't horrendous, it's just something that I noticed. It seems to kick in around 25 miles and hour, and it goes away around 50 and up. Or everything else could just be so loud at 50 and up that I can't hear it. But nothing seems to be moving any differently.

For now, I'm still driving it. I made my 190 mile trip, and survived it, and am keeping an eye on my freshly changed diff fluid (which surprisingly isn't leaking out, despite my hilariously sloppy application of blue RTV), to see if it turns cranky and burned again. Hopefully it holds out.

 

I give you props just for tasting the oil!!!