Rear differential problems

[SuBob]

I have a 99 Outback with a 5 spd. std trans.
The other day I went to back up and the car jerked and stopped, like I had stalled the engine, I didn’t. I put in the clutch quickly and backed up again, this time I had quite a noise coming from the rear end. I drove the car home with no problems except my new noise. The noise is a grinding sound with a clunk about every revolution of the wheel. It lessens at speed and just becomes more of a whirr. I had the oil replaced in the diff. and told the mechanic to watch for metal pieces and he reported he did not see any in the old oil. I have also put the car up on blocks and turned the wheels to see if I could find the problem, CV joint or whatever and and found no problems visually. The only sound I could hear a loud clunking from rear differential when I rotated the rear wheels or twisted the drive shaft so I think I have it located the problem.
Does any one out there have any ideas about what this is. Before I go and possibly tear into it I would like to have an idea of what I am getting onto. Or if I should leave it to pro.

[satan]

as part of your diagnostics, i would recommend pulling the rear driveshaft down and re-trying your "rotate stuff" process - While you do mention that the clunk is once per wheel revolution (this usually points to something from the wheel plate on into the side & spider gears) you may be seeing/hearing something else from the drive shaft (though the drive shaft will spin several times per wheel revolution.

With the drive shaft eliminated from the equation - in my world it's easier to pull the rear cover off of the Differential than to pull the CV shaft. - though I would recommend that you work to eliminate the possibility (and more common) wheel bearing failure as a cause for your noise in most cases.

You may wish to just pull the cv shafts as well to see what end of which cv shaft your noise originates from (wheel bearings make a noise similar to what you describe, then later a wobble if they get that far...)


Listening may be your best tool, if you were closer I'd offer to help you with a set of electronic ears to pinpoint the location of your noise. Good luck!

[porcupine73]

Hm....not sure. If you were definitely hearing the clunk from the rear diff itself then it might be on its way out. Do you think the noise could have been coming from the driveshaft (coming from teh trans to the rear diff)?

I'm not sure how much service can be done on these diffs while installed in teh vehicle. You could probably take the diff cover off and then watch the gears and stuff while someone turns the wheels and see if you see any damaged gears or anthying. But you might not be able to see it from there.

Typicalyl people just pick up a junkyard diff and replace it. Of course you have to make absoltuely sure the drive ratio of the replacement rear diff matches the rear diff you have now. If you go this route you might even be able to find a limited slip rear diff in your ratio that would fit.

[SuBob]

Thanks to both of you for the ideas. I now have a better plan of attack.
I’ll let you know what I find.