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Thread: Differential mount bushing

  1. #1
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    Differential mount bushing

    Hey all,

    I did search a bit before posting this.

    What is the consensus on what to use for the differential bushing? Mine is stock, but I have poly subfame bushings. I feel like when I got the car, the feeling was to use poly subframe and rubber diff mounts to help prevent the trunk floor failure. I am starting to get a lot of rear end chatter when the rear tires spin, and the bushing looks like crap, so I will be changing the diff bushing. Can I go poly without causing trunk floor damage, or is it better to stay stock as a preventative measure? Are there other options besides doing the full on dual ear mod?

  2. #2
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    Quote Originally Posted by bionicbelly View Post
    ... I will be changing the diff bushing... What is the consensus on what to use for the differential bushing?... Can I go poly without causing trunk floor damage, or is it better to stay stock as a preventative measure? ...
    Consensus is stock. The following is but one of many reports.
    Quote Originally Posted by Blacklane View Post
    ... A Poly diff mount(s) can literally rip the car apart.
    BMW MOA 696, BMW CCA 1405

  3. #3
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    I'm not sure stiffening the diff mount will help your problem any. The wheels are made to move up and down independently of the differential, which is solidly bolted to the subframe. If the chatter is being caused by the wheels bouncing as they spin, stiffening the diff mount will have no effect.

  4. #4
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    The consensus is poly RSB's, and stock rubber diff bushing from the 3.0 or M cars (it's reinforced and a bit stiffer).

    Oh, try not to pass out when you see the price of the 3.0/M bushing!!!

    "You don't win silver....you lose gold."

  5. #5
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    Quote Originally Posted by danomite View Post
    The consensus is poly RSB's, and stock rubber diff bushing from the 3.0 or M cars (it's reinforced and a bit stiffer).

    Oh, try not to pass out when you see the price of the 3.0/M bushing!!!


    Yeah,

    I saw that, and promptly decided to inspect mine a little better. See if I can get a few more miles out of the old girl. Three hundred bucks! Unbelievable!

    - - - Updated - - -

    Quote Originally Posted by Blacklane View Post
    I'm not sure stiffening the diff mount will help your problem any. The wheels are made to move up and down independently of the differential, which is solidly bolted to the subframe. If the chatter is being caused by the wheels bouncing as they spin, stiffening the diff mount will have no effect.


    This was posted by another forum member earlier. Can't remember who.

  6. #6
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    Quote Originally Posted by CB750 View Post
    If you buy the M differential cover with the bushing installed, BMW throws in the cover for free (well, not quite...but the bushing pricing has gone wacky)

    M Differential Cover with Bushing $387.93

    M & 3.0i Differential Mount Bushing $278.68

    I checked my ECS Tuning order history; I paid $126.82 for an M differential mount bushing two years ago.
    At the time, I thought that was expensive for such a simple item, but $278 today for the same BMW part is simply ridiculous.
    They've taken a meteoric rise; pretty sure I'd bought them low enough that the list price was <$68.00; that could've been a decade ago, but I replaced on on a non-M a few years ago, citing that it would be an upgrade, and was shocked when I found out the price__and quite apologetic when I explained it to the car's owner!

    Try Ed at BimmerBum.com and see what he can do for you on Lemforder rubber prices.

  7. #7
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    I had the M bushing installed when I had my subframe reinforced a little over a year ago, and it was $190 then. I'll probably rebuild it with window weld whenever it finally kicks the bucket, these prices are asinine.
    2001 Z3 3.0 Coupe--Sterling Gray/Sunroof Delete/5MT

  8. #8
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    Quote Originally Posted by CB750 View Post
    If you buy the M differential cover with the bushing installed, BMW throws in the cover for free (well, not quite...but the bushing pricing has gone wacky)
    You'll also need the longer bolts for the M cover, and maybe the speed sensor pick-up is slightly different (I can't remember).

    Also, good luck finding anyone with one of the finned covers in stock!!! The delivery time on those things is months!

    "You don't win silver....you lose gold."

  9. #9
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    Quote Originally Posted by CB750 View Post
    There is a bonded rubber aftermarket bushing from a company named "Vibra-Technics" available, but I don't know if anyone here has tried it, and while the price is significantly lower than the BMW part, the Vibra-Technics differential bushing is not inexpensive:

    BMW Differential Mount Bush (E30, Z3 and E36 compact)

    I'm using their motor mounts and they are very well built. Wouldn't hesitate to try their diff mount bushing too.
    2001 Steel Gray MCoupe - 147,000 miles and owned since new. MCS 2WNR suspension, Hotchkiss swaybar, poly bushings all around, cat delete headers with custom tune, 3.73 LSD, and Clownshoe Motorsports rear subframe reinforcement.

    2014 Porsche Cayman S / 2022 BMW X3M Competition / 2020 Ram Rebel

  10. #10
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    z3 02' 3.0i coupe, 99M3
    I've had the hardest poly in the subframe and stock rubber diff bushing on my 02' 3.0 since I got it at 6k miles. now at 133K 250+ track days (some double duty the wife & I), SC on since 94k miles. I still have zero subframe issues. That said I am Not a tire burner, neutral drop kinda' guy.

    I did recently change the Poly bushing since well, they do dry out

    2 cents
    bill

  11. #11
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    any updates? curious about the "hardest poly" bushings

  12. #12
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    ...it depands
    As M bushing alternative, 80A poly is also recommended. RevShift makes them in 80A which is the softest available (also the closest to the M bushing) that I could find for a fractional cost.

    [Note] That's what I have installed on my z3, but mine is RF reinforced so it might respond differently to the 80A bushing.
    Last edited by nevan; 02-11-2019 at 12:34 PM.
    2000 Z3 M Titanium Silver / Imola Red+Black Nappa
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  13. #13
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    Quote Originally Posted by nevan View Post
    As M bushing alternative, 80A poly is also recommended... That's what I have installed on my z3, but mine is RF reinforced...
    Does that mean that if you have the RF kit installed to reinforce the trunk floor and the differential mount, that it is then safe to use a hard polyurethane bushing in the differential mount?
    BMW MOA 696, BMW CCA 1405

  14. #14
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    I use the AKG 85A bushing on the diff of my roadster. Car has two rough-looking spot welds that haven't gotten worse in 5 years of abuse. I have the Revshift 95A bushing in my coupe. No issues.
    96 320i Touring
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  15. #15
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    Quote Originally Posted by Vintage42 View Post
    Does that mean that if you have the RF kit installed to reinforce the trunk floor and the differential mount, that it is then safe to use a hard polyurethane bushing in the differential mount?
    That was the thought when I replaced with "80A". I wouldn't go anything harder than 80A though if you want an oem alternative.

    I liked it so much that I replaced the 68D subframe busings with the same hardness also. To my amusement, it handles very much like the OEM Z3M bushing.

    It's been about 5 months so it might be too early to tell. But since then, I've been driving the car pretty hard to test new additions (with occasional wheel hops and hydralic lifters ticks). But it seems to be doing well under there during the last time I did visual inspection.
    Last edited by nevan; 02-11-2019 at 07:05 PM.
    2000 Z3 M Titanium Silver / Imola Red+Black Nappa
    2011 328i E92 Space Gray Metallic / Leder Dakota+Oyster
    Since 1987 12 euros / 2 kdms / 2 jdms
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  16. #16
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    Spot welds that pull through may only tell part of the story; a close inspection under the car will provide a clearer indication of any cracks or separations that may have formed. In my case, I had a 1" crack under the car, on or about where the spot welds failed.
    Tony
    "You can't sign away negligence."

  17. #17
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    Quote Originally Posted by Tim95M3 View Post
    I use the AKG 85A bushing on the diff of my roadster. Car has two rough-looking spot welds that haven't gotten worse in 5 years of abuse. I have the Revshift 95A bushing in my coupe. No issues.
    Similar case here. Two bad spot welds. I meant to buy the AKG 85A bushing for my car, but misclicked and bought the 75D bushing. You'll get a lot more diff whine, but that's about the only difference I can tell. I also get a lot of tire chatter in the wet. I don't spin much in the dry.

  18. #18
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    I did Poly all over, from front to back, but installed rubber for the diff. That did not last. I need to install another one and would hope this will be the last time. I dont know what to do as there is too many different suggestion. All I know is that the rubber one did not last ( I do not use the car a lot: a year, maybe 2 years before it failed?) But I dont know what density I used and I doubt it will say so on the invoice, if I can still find that...

  19. #19
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    Did you buy the OEM brand bushing? Yours may have failed early due to being a cheaper product.

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