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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.

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

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  13. #13
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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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  14. #14
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    Hi all. I have just joined BIMMERFORUMS, so I hope I get this right. My car is a 96 328I convertible which I have owned for almost 20 years (so E36 not E39- but diffs are probably the same. I have the manual transmission version. The car had been pretty much idle for 8 years whilst I had a company car. Then I changed jobs and had to use my BMW again. It has a very low mileage for its age. First thing I did was check the fluids, including the diff oil. With my 14mm Hex key, I opened the diff (bolt was very tight-used a car jack to help) and checked with my finger in the hole and seemed up to the top. After say 3 mths of use I started to hear a humming noise, which I thought was a wheel bearing. After all, I had checked the diff and it was full and there was no oil on the garage floor. The noise started getting worse until one day I came home from work and an oil spill on the drive way.Cleaned up oil from brick paving immediately and stopped using car. I jacked up car and saw oil had started leaking from the left rear side of the diff and down the driveshaft and onto the floor. The boots for the cv joints were fine. I wanted to buy some of that stuff that is supposed to fix leaks but ended up buying a stuff called Moray additive. It took almost 400ml , the diff according to the manual takes 1.7 liter , so I lost a substantial amount of fluid in a very small time cause I never saw leaks on floor before. All I can think is that the seal got dry when the car wasnt used and caused the leak. I have monitored the leak and it is now minimal with Moray in. In fact there is nothing I need to top up. I have just done a oil change on the diff. When I put the Moray in, I used a pipe connected to the bottle to squeeze in the Moray. By mistake I initially sucked in some of the old diff oil and it seemed red in color. Now when I emptied the diff oil (while it was still warm) out came an almost black oil with a whitish colored streak, which disappeared after a while. When I cleaned the pan after I poured the old stuff into another bottle, I could not really find any traces of metal filings / grindings. I filled the diff up with Nulon Synthetic 75W90 after I added a tube of 150ml of Liqui Moly ( a black guey mess that is very expensive but is supposed to make bearings shut up). Also, lot of people told me the diff will only take 1.1 L, but can verify now that it takes 1.7L for definite. I have now driven for a week with Liqui Moly and Nulon in and it still humms...bummer. Maybe I just need to drive it more. I felt there is no point in changing side shaft seal when the leak is now little and there is a chance my diff needs a new bearing. I still wonder though if its a wheel bearing??? After I put the Moray in, it was initially quiet but after a short while driving the noise would start. With the LiquiMoly and new oil , the noise starts immediately. Maybe it needs to be in there for some while before it does anything. Or I need to find another diff.... I would love to hear from other peoples experiences? The car has only done 135000km! I will let you all know what happens...I just hope this Moly stuff works in the end. Being a manual, I can freewheel down hill with engine off and the noise is still there coming from the rear.

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    google TLDR.......

  16. #16
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    Quote Originally Posted by cnn View Post
    Maybe REAR wheel bearings going bad?
    Thanks cnn,

    That's where I am aiming now. One year later. Nothing was done so far...
    The noise from the back is SO LOUD, so the person in the rear can not hear those in front...

    Expecting my 1 Hub (I have one already), 2 Rear Bearings, 8 Collar Screws and 1 Collar Nut (I have one already) in the mail.
    Thanks to your 1998 528i REAR Bearing the Easy Way! write-up! Subscribed...

    Now my current situation is that both ASC+T and ABS lights came on.
    Also, I have a strange feeling that something pulling the car back...

    Does it point to Bad Bearing?

    Thank you in advance,
    siny528i
    BMW CCA 434493

  17. #17
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    yes if the bearing is bad enough. The WSS signal is created by the bearing mounted reluctor rotating in proximity to the WSS. play in the bearing could cause an inconsistent spacing tween the two. what is the ABS code youre getting?

  18. #18
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    Quote Originally Posted by mattmar1 View Post
    yes if the bearing is bad enough. The WSS signal is created by the bearing mounted reluctor rotating in proximity to the WSS. play in the bearing could cause an inconsistent spacing tween the two. what is the ABS code youre getting?
    Thanks mattmar1,
    Sorry for the delay... Did not check that ABS code yet...

    ALSO, I have noticed IMO unusually high revs.
    For example, 4500 at 50MPH and 5500 at 60

    I dont think bad bearings may cause this...

    Thank you in advance,
    siny528i
    BMW CCA 434493

  19. #19
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    Def bad rear wheel bearings fme. Mine was also very loud and I thought it was the tires or diff too...turned out to be a bad wheel bearing. The fact that it changes when turning is a clear indication imo. After installing a new bearing on the rear driver's side (iirc), the loud humming noise disappeared. After that experience, I decided to do the front hub/bearings as well and it was a good thing because they were fried too...

    '00 540iA Sport w/235k+ Original TCG's, Vanos and transmission.​*Trans failure at 244k+...FS Now

  20. #20
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    Quote Originally Posted by ViolinARC View Post
    Def bad rear wheel bearings fme. Mine was also very loud and I thought it was the tires or diff too...turned out to be a bad wheel bearing. The fact that it changes when turning is a clear indication imo. After installing a new bearing on the rear driver's side (iirc), the loud humming noise disappeared. After that experience, I decided to do the front hub/bearings as well and it was a good thing because they were fried too...
    Thanks, ViolinARC!
    Bearings are #1 in my Priority list!
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  21. #21
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    Quote Originally Posted by siny528i View Post
    Thanks cnn,

    That's where I am aiming now. One year later. Nothing was done so far...
    The noise from the back is SO LOUD, so the person in the rear can not hear those in front...

    Expecting my 1 Hub (I have one already), 2 Rear Bearings, 8 Collar Screws and 1 Collar Nut (I have one already) in the mail.
    Thanks to your 1998 528i REAR Bearing the Easy Way! write-up! Subscribed...

    Now my current situation is that both ASC+T and ABS lights came on.
    Also, I have a strange feeling that something pulling the car back...

    Does it point to Bad Bearing?

    Thank you in advance,
    siny528i
    Heya guys,

    Both problems are fixed.

    LOUD Noise is gone after I replaced Rear Bearing and other Rear Suspension parts discussed in:
    Changing Rear Suspension @ 239k... Real PITA!!!

    As per ASC+T and ABS lights on, I found out that the cable to ABS Wheel Speed Sensor was torn.
    After replacing it and driving couple times lights came off.

    Thanks again,
    siny528i
    BMW CCA 434493

  22. #22
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    Nice! With all that done, it'll be like getting a brand new Bimmer!
    Ed CT
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  23. #23
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    Quote Originally Posted by Ed CT View Post
    Nice! With all that done, it'll be like getting a brand new Bimmer!
    Thanks Ed,
    Still need a few things to be done...
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