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Thread: Need help with diagnosing rear end noise - 850 CSi

  1. #1
    Join Date
    Jan 2011
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    Coral Gables, FL USA
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    850 CSi/3.0 CSi/E38 740

    Need help with diagnosing rear end noise - 850 CSi

    Car is making low, groaning noises in 1st gear or reversing; noise disappears when in 2nd gear or above. Is particularly loud when turning at low speed.

    I suspect LSD; recently changed differential oil. Any thoughts on potential cause?

    I am about 1K miles from home, and concerned with making a minor issue into a major one by continuing my drive.

    All help appreciated!


    Ray
    Riding the Depreciation Curve....

  2. #2
    Join Date
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    Funny you should mention this, I had my LSD rebuilt with new clutch plates installed recently. I noticed today that when I reverse turning, or pull forward slowly turning, I feel a rumble/groan coming from the rear. I know everything is new back there, so I'm guessing it the LSD kicking in.

    - - - Updated - - -

    http://www.m3post.com/forums/showthread.php?t=144569

    - - - Updated - - -

    Does it sound like your tyre is rubbing on the wheel arch? that's what mine sounds like. Apparently this happens after fluid change, you can put an additive in there to get rid of it. Do you know what diff oil you used?

  3. #3
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    My LSD was a groaner on corners - so I added Lubegard LSD additive - and that made absolutely no difference! But using specific LSD fluid did as described here:

    http://www.meeknet.co.uk/e31/BMW_E31...al_Service.htm
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  4. #4
    Join Date
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    Thanks for the replies Timm & Omega Man; new +1 tires & new lube- have to check my records on lube type. Will have to wait to get home to further diagnose- and yes, it sounds like tire rub.

    Ray
    Riding the Depreciation Curve....

  5. #5
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    I have Syntrax LSD oil in mine. Some people drive their car in a figure 8 pattern in an empty car park for ten minutes ….


    Like this http://www.m3post.com/forums/showthread.php?t=254249

  6. #6
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    When you change your rear diff fluid....

    ALWAYS make sure you can get the fill plug out FIRST!

    The last thing you want to do is to open the lower drain plug only to find some fool torqued the upper fill plug to 8000 pounds or something crazy. It is not a good day when you open the lower drain plug first, then find out that you cannot get the upper filling plug out to put the new oil in.
    CSi #18 - Car & Driver Magazine 1994 actual test car
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  7. #7
    Join Date
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    Am assuming from your location that your CSi is a US-spec car - without AHK?
    ECE-spec CSi's (with AHK as standard) emit a low frequency 'drumming' noise when setting off, which is simply the AHK system doing a self-test.
    If your rear tires are concentric and not bulged, I suspect your noise could be either differential-related, or possibly even worn subframe bushings?
    Attached Images Attached Images
    Current:
    1994 E31 850CSi Sterlingsilber/Anthracite Buffalo

    Previous:
    1987 E28 M5 Delphin
    1986 E23 M745iA Arctic Blue
    1986 E24 635CSi Polaris
    1976 E3 3.0 Si Arctic Blue

  8. #8
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    You need to use 85w-140 gear oil WITH LSD friction modifiers. If not you will have a noisy diff.
    If that's not it your bearings are on their way out, not a big deal takes a while for them to completely go.
    If in fact diff needs to be rebuild I can supply the rebuild kit as well as more favorable gear ratio for the rebuild or a separate unit entirely saving you labor cost.

  9. #9
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    Good advice, Roger, Thanks.

    - - - Updated - - -

    Quote Originally Posted by kiwiCSi View Post
    Am assuming from your location that your CSi is a US-spec car - without AHK?
    ECE-spec CSi's (with AHK as standard) emit a low frequency 'drumming' noise when setting off, which is simply the AHK system doing a self-test.
    If your rear tires are concentric and not bulged, I suspect your noise could be either differential-related, or possibly even worn subframe bushings?
    US spec CSi- thought it may be bushings, have to get car on a lift.

    Ray

    - - - Updated - - -

    Quote Originally Posted by dragon850 View Post
    You need to use 85w-140 gear oil WITH LSD friction modifiers. If not you will have a noisy diff.
    If that's not it your bearings are on their way out, not a big deal takes a while for them to completely go.
    If in fact diff needs to be rebuild I can supply the rebuild kit as well as more favorable gear ratio for the rebuild or a separate unit entirely saving you labor cost.
    Good to know, heading back home now to get a better diagnosis.

    Thanks,

    Ray
    Riding the Depreciation Curve....

  10. #10
    Join Date
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    Quote Originally Posted by kiwiCSi View Post
    Am assuming from your location that your CSi is a US-spec car - without AHK?
    ECE-spec CSi's (with AHK as standard) emit a low frequency 'drumming' noise when setting off, which is simply the AHK system doing a self-test.
    If your rear tires are concentric and not bulged, I suspect your noise could be either differential-related, or possibly even worn subframe bushings?

    I have heard that noise a few times, never seen it explained by BMW though. Thanks.

  11. #11
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    are slow
    These diffs love to leak at the output seals and absolutely will groan without additive, keep that in mind.

  12. #12
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    Quote Originally Posted by Omega man 1969 View Post
    I have heard that noise a few times, never seen it explained by BMW though. Thanks.
    No worries, it's a handy tip that not many Euro-CSi owners are aware of - potentially saving hours of troubleshooting an elusive rear-end noise.
    Refer to Section 33-34 of the online E31 Repair Instructions for more AHK info.
    Current:
    1994 E31 850CSi Sterlingsilber/Anthracite Buffalo

    Previous:
    1987 E28 M5 Delphin
    1986 E23 M745iA Arctic Blue
    1986 E24 635CSi Polaris
    1976 E3 3.0 Si Arctic Blue

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