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3B Diff output flanges vertical play

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  • 3B Diff output flanges vertical play

    Evening chaps.

    My rear diff is leaking and need to get round to sorting it. However due to the vertical play in the output flanges, I would say somewhere in the region of 2-3mm, is there any point in replacing the seals. Surely they will just start leaking again with this amount of movement?

    Also I seem to have a slight vibration on overrun at around 30-40mph. Not sure when it started, only recently I noticed it. Hard to say where it's coming from but would this play be a contributor? If I apply the slightest of throttle the vibration seems to smooth out. Strange!

    What is the fix for for this, is this amount of play excessive?

    Cheers lads
    Gordon




  • #2
    Infact this vibration is getting worse. Just been out for a thrash and you can feel a strong vibration though the car. It wasn't to bad whilst just cruising around, a vibration could be felt around the 30-40mph zone, however after a spirited drive it was a lot worse. It feels like the back end, I think this diff might be suspect. I just don't like the amount of play in these output flanges!!!

    Anybody else have vibration issues from the rear diff?

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    • #3
      I think there is a tapered bearing in there that might have failed. One on each side according to 7zap. I have no idea how you would change them mind
      Nothelle S2 Avant in restoration
      Wr Ur Quattro (also in restoration)

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      • #4
        I've no idea either, not something I've looked into. I'm wondering if this is a common problem on these cars, my car just ticked 150k a few days ago so not excessively high mileage. If my diff has this amount of play I would think most others with similar miles would be the same.

        I changed my prop bearing a couple of days ago and the shafts are nice and straight. Everything was returned to the position it was in previously. I felt this vibration for the first time one night before I replaced the prop bearing so the problem lies elsewhere.

        The flanges must be rattling around in there causing the vibration surely?

        Last edited by gmac78; 16 September 2020, 09:12.

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        • #5
          There was no noticeable play in mine when I overhauled it during my 're build. Play as you describe needs urgent attention. It's probably run out of oil at some stage in its life. These diffs are normally very durable.
          Nothelle S2 Avant in restoration
          Wr Ur Quattro (also in restoration)

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          • #6
            I drained and refilled with oil a few years back, however looking on the outside of the diff it's been leaking for some time. Might not be much oil left in it now actually. The play in these flanges is too much though and needs addressed one way or another.

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            • #7
              The drumming/vibration noise is the driveshafts moving eccentrically because of the play in the bearings, essentially it puts them out of balance.

              Much the same as when a CV gives out.

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              • #8
                Originally posted by Bowie69 View Post
                The drumming/vibration noise is the driveshafts moving eccentrically because of the play in the bearings, essentially it puts them out of balance.

                Much the same as when a CV gives out.
                Yeh I guess you're right enough there, makes sense. I had to drive the car 15 miles today to it's resting place for the next few weeks and the vibration the whole way was not nice!!! Again, at it's worst around the 30-40mph zone but present the whole time now.
                Last edited by gmac78; 16 September 2020, 19:42.

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                • #9
                  Mine has 479 000km on the original rear diff. It has had a very noticeable vertical play on the right side output flange for at least last 200 000km maybe 300 000km. Does not leak, does not make noises. I can't remember how it is on the left side. These are tough units. You may want to check for other sources for that drumming before attacking the diff.

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                  • #10
                    Originally posted by JariP View Post
                    Mine has 479 000km on the original rear diff. It has had a very noticeable vertical play on the right side output flange for at least last 200 000km maybe 300 000km. Does not leak, does not make noises. I can't remember how it is on the left side. These are tough units. You may want to check for other sources for that drumming before attacking the diff.
                    Well that's interesting I must admit!!! If you've covered that amount of mileage with noticeable play and no vibration it maybe good news for me. I've not had a chance to put it on a ramp yet but will do over the next few days. It should be quite obvious where it's coming from if I spin the wheels whilst on a two poster.

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                    • #11
                      When those kind of bearings start to go bad, they usually start with a whine. If it has oil, it will whine a long, long time before anything major happens. When it gets to vibration and drumming, then it's ready to blow up. Maybe you should put your car on a lift and have a listen with stethoscope while turning the wheels by hand. It's easy to spot a bad bearing like that just poking around with the stethoscope and listening.

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