Legacy rear differential troubleshooting

pella2pella2 Member Posts: 5
Hello all. I have encountered a new problem with my 1990 Legacy. There is a noise coming from the rear (right side it seams) that is pretty noticeable at slow speeds, <5MPH or less. It sounds as though something is loose. I definitely sounds like a gear issue to me. The car has 223K miles on it and has an automatic transmission which shifts fine.

I put that car up on jacks and checked the DOJs and they are tight. The boots are not ripped and are in good shape. There is a little slop laterally on both axles which seems normal to me. There is some up and down movement at the oil seals where the DOJs connect. The wheel bearings are tight.

I turned on the engine and put it in gear and I did not hear anything abnormal from under the car. What I did notice was that the right rear intermittently engaged slightly while the the left rear was rotating. I would have expected it to not engage at all unless the left rear was held. Is this indicative of a differential problem? Is there other troubleshooting that I can do? Could the noise disappear when the car is jacked up. I do not see anything loose under the car.


  • dcm61dcm61 Member Posts: 1,567
    Have you checked the rear brakes ... the disc pads as well as the parking brake shoes?
  • pella2pella2 Member Posts: 5
    Yes I did. Sorry for not mentioning that earlier. The brakes and rotors are new as of a couple of months ago. I removed the rotor and inspected them. All OK there.

    Thanks for the reply.
  • ateixeiraateixeira Member Posts: 72,587
    On an open diff, if you spin one wheel forward the other will spin in reverse.

    With a limited-slip they move in the same direction.

    At least that's how it is with viscous LSD and open diff Miatas. That's the test we'd used to see if a diff was limited-slip and still worked.
  • xwesxxwesx Fairbanks, AlaskaMember Posts: 16,034
    What I did notice was that the right rear intermittently engaged slightly while the the left rear was rotating.

    Okay, so that's a problem. If you had both wheels blocked with no resistance, both tires should spin with equal momentum on any differential. If it is an open differential, any resistance to either tire will transfer the power to the other tire. On a limited slip differential, the axle should resist any efforts to stop one tire while the the other is spinning.

    If yours is only intermittently engaging (slightly), then it sounds like there's a problem in the differential. When's the last time the fluid was changed in there?
    2018 Subaru Crosstrek, 2014 Audi Q7 TDI, 2013 Subaru Forester, 1969 Chevrolet C20, 1969 Ford Econoline 100, 1976 Ford F250
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