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Thread: Suspension Bushing/Mount Refresh + Oil Pan & Steering

  1. #76
    Join Date
    Feb 2009
    Location
    Mills River, NC
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    1,118
    My Cars
    95 M3 coupe, 97 M3 sedan
    You're feeling normal engine and driveline vibrations that are now amplified by stiff mounts. As a quick & easy experiment, if you swap back to stock rubber transmission mounts and drive around you'll find the NVH drops dramatically.

  2. #77
    Join Date
    Jun 2005
    Location
    New England
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    25,402
    My Cars
    F90 M5; E36 M3 Turbo
    Quote Originally Posted by TostitoBandito View Post
    Tightened up the mounts and I still have the odd vibration when lifting off the throttle while in gear. It's subtle at low speeds and more noticeable at high speeds. I was thinking maybe the drive shaft (or guibo/CSB/u-joint), but I find it odd that acceleration is smooth and it only occurs right after I lift. I'd expect that to cause vibrations anytime it's spinning. At freeway speeds is vibrates like a mild rumble strip for about half a second after lifting.

    Any ideas? Is this just normal engine braking transmission noise which I'm now feeling for the first time due to the stiff mounts?
    Maybe the stiffer trans mounts.

  3. #78
    Join Date
    Aug 2013
    Location
    Seattle, WA
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    1,433
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    1999 BMW M3 Coupe
    Yeah that's what I'm thinking. I've got no issue with the NVH really (in fact I love most of it), I just wanted to make sure this specific vibration wasn't indicative of an issue. I'll keep an eye on it and continue to tweak the mounts as necessary.
    1999 M3/2/5 - Titanium Silver - Track/Weekend Toy


  4. #79
    Join Date
    Feb 2009
    Location
    Mills River, NC
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    My Cars
    95 M3 coupe, 97 M3 sedan
    Tweaking the mounts won't change anything. Just torque to spec and recalibrate your brain to the new level of NVH.

    As I mentioned before I HATED poly trans mounts in a street driven E36. It seems to be more of an issue for me in this car because the engine is quite smooth compared to most, especially if you have a stock dual mass flywheel. Any small increase in NVH becomes immediately noticeable... really stands out. I went through the same thought process as you, thinking something had to be wrong. It's not. It's just that poly mounts make the car feel rougher.

    Having said all that, the same M3 I drove on the street years ago is now track only. It has 75D engine/trans/diff mounts, delrin front lower control arm bushings and spherical bearings at all rear suspension pivots and shock mounts. It also has an extremely noisy Tilton race clutch. The level of NVH at slow speeds is completely overboard, but also completely disappears on track where throttle input is on/off. I can't imagine driving it on the street at partial throttle. It literally sounds like parts are falling off the car when I drive through the paddock.

    I guess what I'm trying to say is over the years I've run everything from stock rubber parts to sphericals and everything in between. What makes a good track car tends to make a bad street car and vice-versa.

  5. #80
    Join Date
    Aug 2013
    Location
    Seattle, WA
    Posts
    1,433
    My Cars
    1999 BMW M3 Coupe
    There's no "torque to spec" to these poly mounts. The instructions are more or less to tighten until the bushing begins to "bulge", then back off slightly. This isn't too difficult for the softer cylindrical trans mounts where it doesn't take much, but the harder and larger motor mounts don't really bulge or deform, at least not until you get them damn tight. That's what I'm still tweaking. I definitely had them too loose initially, because tightening them this past weekend reduced low RPM NVH.

    But yeah, I hear you on the street/track thing. I'm trying to toe the line in the middle as much as it's possible to do. I have a pretty high tolerance for NVH and I don't really drive a ton of street miles. I've had my GC suspension with linear springs on it for several years, for example. Then I did an intake and exhaust, and now I stiffened up the suspension and mounts to a level that's firmer but still way more civilized than solid delrin/aluminum. I've been in racecars before, and my car is nowhere near that level of sounding like "someone hitting metal with a sledgehammer" when shifting or braking or anything else. It's just an adjustment from many years on rubber and wanting to make sure I don't have anything legitimately broken. It's growing on me already.
    1999 M3/2/5 - Titanium Silver - Track/Weekend Toy


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