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Thread: LOUD HUMMING Noise From The Rear... Low Differential Oil?

  1. #1
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    LOUD HUMMING Noise From The Rear... Low Differential Oil?

    Heya guys,

    Recently I've noticed a VERY LOUD humming noise from the rear of car. It almost unbearable on the highway.
    It does not sound like bearings. I tend to believe my Differential is LOW on Oil.

    Being at 230,936 and not sure if Differential Oil was ever changed, I think I gotta do it ASAP.

    Now, I found few cute DIYs how to do it, but my concern is about what Oil to choose.
    Can I use BMW Differential Oil (P/N 07-51-2-293-972, http://www.ecstuning.com) for the job?

    Thank you in advance,
    siny528i
    Last edited by siny528i; 10-11-2018 at 03:22 PM.
    BMW CCA 434493

  2. #2
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    Any synthetic gear oil of the proper weight and type should be fine, there are lots of threads on it. Are there signs it has been leaking?!?

    In any case, if the oil was low, adding more can't hurt but quite likely significant damage has been done that new oil can't save. Differentials while simple devices, have quite small tolerances and go downhill quickly outside of them. Not to mention metal bits in bearings. For sure when you drain the oil look for metal. If your drain pans are quite dirty (like mine) you can drain into something else or even strain it. Also if possible (I don't recall the plug locations off hand) use a light and / or scope and take a look at the ring/pinion gear surfaces through the plug holes and make sure they are not grooved. The faces should still be near mirror smooth I should think even with that miles on a healthy diff.

  3. #3
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    Quote Originally Posted by qcdstick View Post
    Any synthetic gear oil of the proper weight and type should be fine, there are lots of threads on it. Are there signs it has been leaking?!?

    In any case, if the oil was low, adding more can't hurt but quite likely significant damage has been done that new oil can't save. Differentials while simple devices, have quite small tolerances and go downhill quickly outside of them. Not to mention metal bits in bearings. For sure when you drain the oil look for metal. If your drain pans are quite dirty (like mine) you can drain into something else or even strain it. Also if possible (I don't recall the plug locations off hand) use a light and / or scope and take a look at the ring/pinion gear surfaces through the plug holes and make sure they are not grooved. The faces should still be near mirror smooth I should think even with that miles on a healthy diff.
    I dont think there is a damage. At least I hope so.

    Their website says that BMW Differential Oil (P/N 07-51-2-293-972, http://www.ecstuning.com):
    "Not to be used with a limited slip differential"

    What does it mean?
    Am I good to go with it?
    BMW CCA 434493

  4. #4
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    Quote Originally Posted by siny528i View Post
    I dont think there is a damage. At least I hope so.

    Their website says that BMW Differential Oil (P/N 07-51-2-293-972, http://www.ecstuning.com):
    "Not to be used with a limited slip differential"

    What does it mean?
    Am I good to go with it?
    That oil is fine. As frankly most any 75w90 synthetic gear oil, choose your flavor. Your car should not have a limited slip differential.

    As for your diff, I'm glad you hope it is. But healthy differentials don't make loud noises. At a minimum, some whine under load could merely indicate improper lash which is noisy but not particularly damaging. Unfortunately, assuming you are dealing with a factory BMW differential that used to be quiet (as opposed to one that's been apart and improperly set up by someone after the fact) your lash would have no reason to have changed. That leaves noise from excessive wear, which generally results from improper lubrication, and new oil will not undo that damage. Again, I would highly recommend looking at both the oil that comes out, and if at all possible the surface of the ring / pinion themselves.
    Last edited by qcdstick; 10-11-2018 at 04:48 PM.

  5. #5
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    I use Redline fluids.

    I wrote a DIY using "Gravity Fill" (clear tubing + funnel) some 12 years ago.
    Report back what you find after fluid change.
    I thought the rear diff lifespan is some 300K-400K, may be I am wrong...

    http://bimmerboard.com/forums/posts/189240

  6. #6
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    Quote Originally Posted by qcdstick View Post
    That oil is fine. As frankly most any 75w90 synthetic gear oil, choose your flavor. Your car should not have a limited slip differential.

    As for your diff, I'm glad you hope it is. But healthy differentials don't make loud noises. At a minimum, some whine under load could merely indicate improper lash which is noisy but not particularly damaging. Unfortunately, assuming you are dealing with a factory BMW differential that used to be quiet (as opposed to one that's been apart and improperly set up by someone after the fact) your lash would have no reason to have changed. That leaves noise from excessive wear, which generally results from improper lubrication, and new oil will not undo that damage. Again, I would highly recommend looking at both the oil that comes out, and if at all possible the surface of the ring / pinion themselves.
    Thanks qcdstick!

    Honestly, I do not know when there is a lot of noise or little, because I have nothing to compare with.
    Also the noise that I hear without the rear seat installed.

    In addition, when I drive along a winding road, the noise almost disappears when I am turning right.
    Maybe in the end it's the bearings?

    Thanks again,
    siny528i
    BMW CCA 434493

  7. #7
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    Quote Originally Posted by cnn View Post
    I use Redline fluids.

    I wrote a DIY using "Gravity Fill" (clear tubing + funnel) some 12 years ago.
    Report back what you find after fluid change.
    I thought the rear diff lifespan is some 300K-400K, may be I am wrong...

    http://bimmerboard.com/forums/posts/189240
    Thanks cnn!

    I know. Your DIYs awesome.
    That's exactly what I am going to use.
    I will definitely report back...
    BMW CCA 434493

  8. #8
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    Maybe REAR wheel bearings going bad?

  9. #9
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    Quote Originally Posted by siny528i View Post
    Thanks qcdstick!

    Honestly, I do not know when there is a lot of noise or little, because I have nothing to compare with.
    Also the noise that I hear without the rear seat installed.

    In addition, when I drive along a winding road, the noise almost disappears when I am turning right.
    Maybe in the end it's the bearings?

    Thanks again,
    siny528i
    Diff noise may come and go with the application of power, but shouldn't change based on turning left or right unless you've somehow very badly damaged the planetary gears. Be a good time to change the oil and check it out anyway as a PM. Could easily be a wheel bearing, or something rubbing in the brakes, dust shield... Just i guess depends on what sort of noise it really is, hard to say from here.

  10. #10
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    Quote Originally Posted by qcdstick View Post
    Diff noise may come and go with the application of power, but shouldn't change based on turning left or right unless you've somehow very badly damaged the planetary gears. Be a good time to change the oil and check it out anyway as a PM. Could easily be a wheel bearing, or something rubbing in the brakes, dust shield... Just i guess depends on what sort of noise it really is, hard to say from here.
    I understand. Maybe this sound will help a little:

    http://cyberforma.com/auto/issues/bm...s/20181011.mp3

    Thanks again,
    siny528i

    BMW CCA 434493

  11. #11
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    Man, I don't know. That sounds like a single cylinder engine exhaust note more than anything, lol.

    I don't know how fast you were driving, but it's probably a U joint in either the driveshaft or halfshafts. Probably a half shaft if it changes with the suspension loading / unloading.
    Last edited by qcdstick; 10-12-2018 at 09:36 AM.

  12. #12
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    This is the stuff that Mike Miller, from BMW Roundel magazine Tech Talk column, recommends.

    https://www.amazon.com/dp/B000CPCBF0...v_ov_lig_dp_it
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  13. #13
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    geargrinder is offline Having No Trouble Here BMW CCA Member
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    IF its side-related - comes and goes in turns - I like half-shaft/CV or wheel bearings over the diff. Doesn't mean you shouldn't change your diff oil, but I'd get it up in the air, and spin each side and see what you hear and feel, jank around w/ the axles, see if one CV is really boogered up or anything.
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