On my 85 4runner I'm hearing a noise coming from the rear end. It sounds kinda like the noise big knobby tires make while going down the road. The only problem is I don't have knobby tires and it only does it when I hit the gas. When I let off the gas it quits making the sound.

How loud is the noise?
Are there any driveline vibrations with it?
Is it coming from the middle or from the wheels?
Can you crawl under, try to rotate the driveshaft at the axle and feel any slack?

The noise is loud enough to where I can hear it over the radio. Not extremely loud just annoying. About the same amount of noise as knobby tires on pavement. Of course the faster I go the louder the noise. It doesn't start until I get up to about 25-30mph. It seems to drive smooth just noisy. As soon as it quits raining I'll check for the slack.

also check your diff fluid and u-joints..

-Scerb

I second U-Joints

3rd on u joints. how many miles on your diff? I just had to replace mine because it was growling... kind of like what you describe. Are you losing any fluid back there?


I would check u-joints, then jack it up and check your wheel bearings. Also make sure your drums are okay. I mean, start with the easier things first.

Are the backing plates wet with gear oil, if so it is axle bearings.

I'm going to vote for bearings. Those are the same symptoms I had on my Chevy and my Ford. Both cases had bearing issues. Good news is it won't be that expensive.

I'm not saying it isn't a u-joint, it just sounds more like something bad in the diff itself.

Good luck,
James

If the driveshaft feels solid (no slack or play), there isn't any gear oil leaking at the bearings (it usually slings out all over the inside of your tire), and there is the proper amount of oil in the diff housing, then maybe you can jack it up, start it, put it into gear and see if you can isolate the sound while the wheels are spinning in the air. Mind you, this is potentially one of those "hey, watch this" moves, so be very careful. Or, if you have somebody you don't like much, you can have them hang off the rear bumper while you are driving down the road. Just kidding, but seriously, this is one of those noises that only happens while you drive and can be hard to figure out, until it gets a lot worse, or breaks altogether. Just try to isolate where the sound is coming from exactly, and diagnose from there.

Pull it apart. Don't guess. could be something simple like wheel bearings, could be something bad as my rear diff...

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