Hey all

Need some advice on identifying a noise pretty sure is coming from the rear axle. I don't have a whole lot of experience in this arena so I'll describe best I can.

Noise at slow speeds I can best describe as a scraping. If I'm going slow enough (~10mph) I can hear this "scrape" on each rotation, almost like something spinning has a high spot that hits once per rotation. Speeds up as ground speed increases. Higher speeds its more like a hum. Highway speeds can't hear over wind noise.

I can't say for sure it isn't brakes, but my gut says it's not. I did have a shop look at the brakes when I bought it, they didn't find anything but also were not looking specifically at this noise, they were just giving them a once over.

I can't discern a difference between turning or going straight, or having a load (which is uncommon anyways). Will persist on deceleration. I changed fluid when I got the truck a couple thousand miles ago. Didn't change the noise and for some reason I didn't inspect closer when I had the cover off, but no chunks of metal.

My dad is suspecting spider gears, but wouldn't this show itself more while turning?

I might be overthinking things, it's pretty uncommon for anything besides wheel bearing or worn ring and pinion - right?

If it matters it's a 98 half ton, Chrysler 9.25 no limited slip with 3.55s. 190k miles and little idea how it was treated before I got it other than the girl told me it had big tires on it.
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The differential carrier bearings are also rotating at wheel speed. Typically the noise changes between load and coasting if the problem is with the ring & pinion or the carrier bearings so I'd exclude that for now. Could still be something with the brakes, otherwise axle shaft bearings or maybe even some metal debris picked up in a tire. I'd put the rear axle on jack stands and turn the wheels slowly.

 

We put it on stands and the noise persisted but we were in the garage so difficult to tell if the noise changed. We go to the one drum off the other was stuck too much for how much time we had.

 

Reminds me when the drive shaft ujoints went bad. That's where I'd look. Cheap and easy.

 

What would I be looking for? I've checked it for obvious slop, not sure outside of that.

 

They could still be dry. Take the drive shaft off at the rear axle. See if the u-joints move easily and feel smooth. My guess is brakes.

 

Ujoints can fool you all the way to actually removing them. Only way to tell is close inspection. Otherwise, I'd be looking at the brake drums for proper adjustment then the pinion bearing.

 

Drive down the road and have someone follow you. They need to watch for any wobble in the wheel on either side. Your description doesn't sound like a gear problem. More like a drum rubbing or bent rim or axle.

 

A bent dust shield rubbing the drum, or rust build up on the drum rubbing on the dust shield. When I lived in the rust belt in upstate NY, it was one thing I did with rear drum brakes. Beat the rust off the inside of the drum, put it on and turn it, if I heard scraping, I'd beat some more rust off. Never had any customers return with a problem, don't hammer to hard, you'll be buying new drums. Could also be the infamous "ridge" that develops on drum brakes, as the shoes wear, the drum wears, and what the shoe doesn't contact rusts, on the very outside edge of the drum a ridge develops, it could be scraping the edge of the shoes as it goes around, and it'll also keep you from getting them off. If they turn easy, and suddenly get hard to turn as your pulling them off, that's the ridge. I've had to use a slide hammer to get them off before. New shoes, and hardware kit, and a cutting bit in a die grinder to get rid of the ridge.

 

Rebel has some good ideas there.

I would also spend some time inspecting the brakes. It could be as simple as an out of round drum.