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    Need rear diff

    Hi guys,


    Is anyone looking to part with a 3.91 rear diff? Mine has 300,000 miles on it and is getting pretty noisy.


    Regards,
    Steve

    #2
    I don't have one I'm not using, but if the gears aren't worn, then new bearings should fix it right up. No shimming required if you're just replacing bearings.

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      #3
      Yeah it may just be worn out bearings. If not and you are willing to jump to the 4.10 ratio, I have a front/rear set that I’m pulling this weekend.
      In-Force:
      1991 325iX - DiamantSchwarz - Metallic
      1979 Chevrolet Monza 2+2 - Canary Yellow

      Retired/Sold:
      1991 325iX - DiamantSchwarz Metallic
      2002 325i w/ 235k miles - AlpineWeiß
      2002 Saab 9-3
      1972 Fiat 124

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        #4
        Oh, interesting. I thought a whining diff meant worn ring and pinion gear. I'll take it out in a few days and have a look. Thank you.
        Last edited by s_hemphill; 02-15-2019, 10:26 PM.

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          #5
          Here it is. I haven't taken a diff apart before and I don't have the knowledge to tell whether what I'm looking at is appreciable wear, but I assume this isn't much. There is a bit of play when rotating the output flanges in opposite directions as well as when rotating the input flange and holding one of the outputs. FWIW, the diff would make noise when cruising and tapping on the gas. Let me know what you think.https://imgur.com/a/51cp6Ob
          Last edited by s_hemphill; 02-17-2019, 06:56 PM.

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            #6
            Looks like you have an extra deep pattern on the coast side, which is what you'd expect from a worn forward pinion bearing.

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              #7
              Pretty sure my pinion bearing is going bad too - makes noise on throttle and when coasting in neutral. Hey, it only has ~280,000 miles of hard use..
              Build thread

              Bimmerlabs

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                #8
                Thank you, sir.

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                  #9
                  There's PLENTY of material on the interwebnets about how to set up a ring & pinion, read the pattern, etc. Go do some reading.

                  You can also inspect the contact areas of the teeth for wear. That would show up as undulations, surface cracks, roughness as though material in the middle of a contact face has chipped away, chips off the corners of teeth. I don't see anything alarming on that photo you posted, but gears are tough to inspect in photos.

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