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Suspension Bushings...

Discussion in 'E39 (1997-2003)' started by JDiazAmador, Mar 31, 2010.

    • Member

    JDiazAmador

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    I'm going to be replacing the front shocks on my 2000 528i with Sport Package (shocks will be Sachs sport package which I understand are basically the same as OEM). One of the front shocks is leaking. As far as I know the are the original ones.

    I'd like to take care of any other items that can be handled while the front suspension is apart. I think most of my bushings are OK, since there is no vibration at highway speed.

    Does any company offer polyurethane bushings for the stock sway bars? I remember that from my car-crazy youth as a cheap and easy way to make the sway bar a little tighter without replacing it.

    Sport package front bar is 24 mm (for I-6 engine). I would plan on replacing the rear sway bar with either the stock M5 part (16.5 mm) or the Dinan (17 mm), depending on cost. I prefer a more neutral handling balance, instead of "stock understeer".
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    bcweir

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    Polyurethane bushings are going to be harder than the original

    This is also going to affect your ride quality.

    Do you plan on taking this car to the track? Are all of the streets in your locality as smooth as glass?

    Polyurethane bushings differ from rubber bushings in the regard that they don't compress and stretch the way rubber bushings do. They have a very slight amount of flex but not much.

    These bushings were initially developed for track use, where ride comfort is not nearly as important as increased control on the track. Since this application is not likely to see uneven surfaces and potholes on a paved and maintained race track, they would only appear to last longer than rubber bushings because they're not being subjected to the same ride environment as a street car.

    You can use these for the track if you don't mind the loss of ride comfort in exchange for better control, but don't be surprised if you find yourself replacing these after they crack in six to twelve months due to using them on poorly maintained streets and roads.

    By the way, did you check to see if that swaybar is compatible with your car? As I recall, the M5 uses a completely different suspension system from non-M cars. Not all M5 parts interchange as a straight bolt-in, and an M5 differs in a whole lot more than just body parts and drivetrain.

    Just my $.02, but I think paying extra for urethane for a car that won't see a race track is a waste of money, and the loss in ride quality might not be an acceptable exchange in the bargain.

    Up to you. Godspeed!
    • Member

    Brian A

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    Its a big deal changing Control Arm bushings to polyurethane since a lot more road shock is transmitted to the frame. I'm not so sure about swaybar bushings; swaybars don't get a lot of 'impact" shock transmitted to them.

    I have polyurethane swaybar bushings on both my E30s (Eibach kits) and when I switched from stock, I didn't notice any difference in noise. "Ride quality" was improved, but just because the stifffer swaybars reduced body roll a little, which I liked. Likewise, since the Eibach kit is adjustable, I was able to tune the under/oversteer on the car more to my liking.

    Sorry: can't answer your original question about a source for polyurethane bushings for stock swaybars. Doesn't seem like it would do much for performance though. Swaybars only get a twisting force through them, so rubber or poly shouldn't matter.
    • Member

    JDiazAmador

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    I made many changes to the suspension on my first generation (1984) Mazda Rx-7. Polyurethane sway bar bushings do not make a big change in ride quality, because most of the time the sway bar is going up and down "together" (both ends at the same time).

    It's only when a bump is felt on only one side of the car that firmer sway bars will make the ride quality harsher. I think it's a good trade-off for the reduced body roll. Increasing sway bar stiffness also seems to improve the steering, because the car rolls less before beginning to change direction.

    I've heard all the rear sway bars on the E39 are compatible, and the front bars are only different between I-6 and V-8 cars.

    E39 Sway Bars (mm):

    Stock: F: 22.5 R: 13
    Sport Pkg: F: 24.0 R: 14
    M Sport II: F: 25.0 R: 15
    E39 M5: F: 27.0 R: 16.5
    Dinan (I6/V8): F: 25/28 R: 17
    • Member

    bcweir

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    You can go to realoem.com if you want to see your suspension

    If we're talking basic suspension physics, you're correct. But if you're doing an apples to oranges comparison between a 26-year or older Japanese sports car and a 10 year old German sports sedan, your comparison may come up short of the facts in some ways.

    The only thing that a first generation RX-7 has in common with an E39 BMW is that they're both automobiles. The two vehicles are completely different and have almost nothing in common with one another. Auto technology changed a lot between 1984 (the last production model year for the 1st generation RX-7) and 2000. What's true for a first generation RX-7 is not necessarily true for an E39 5-series.

    It's best to view each car in their own merits, and not on a very limited comparison with one another.


    http://www.realoem.com


    It's helpful if you have the last 7 digits of your VIN number, or if you know the month and date of manufacture for your vehicle (this should be on a label on your driver's side (left front) door jamb). BMW is constantly making running changes to these cars, so knowing this information will usually help bring up the correct information.

    Don't believe everything you hear -- especially if your source didn't bother to check to be certain. You're not the first person, or the last, to make a very expensive purchase error based on an assumption and not checking to be sure. An E39 M5 isn't just an E39 with a hopped up engine.

    The figures you stated are just measurements. They say nothing about suspension type, design, mounting points, types and sizes of the bushings. IF measurements were all that mattered, you could simple weld a steel girder to your rear suspension and call it a anti-roll bar.

    Tahoe guest

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    Is it the left (driver's) side front shock that appears to be leaking. It may not be the shock leaking at all. The power steering reservoir is famous for leaking at the cap on e39s. I replaced the gasket on mine and it stopped for a little while but leaks again. I would not recommend polyurethane bushings on your car. Remember it's supposed to be a luxury performance sedan. It will never be a Lotus. I put an M5 rear bar on my 540i/6 with stock sport suspension because it was recommended as an inexpensive upgrade to help neutralize handling but frankly, I didn't like it much. The car felt light up front at speed. The real improvement came by replacing both front and rear bars with Eibach bars. Those and the stock sport suspension are sweet.
    • Member

    bcweir

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    Sounds like you found a better plan, Tahoe

    You've got some great ideas
    • Member

    JDiazAmador

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    ...Except that they are both rear wheel drive, and both have nearly 50/50 weight distribution.

    Obviously the RX-7 has a much cruder suspension than the E39. It was made up of parts that were already in the Mazda "parts bin" because Mazda did not know if the car would be a success.

    1st Gen RX-7 (last model year 1985), were notorious for oversteer. It was caused by a live axle that could not match the car's roll angle. The outside rear tire would eventually start to roll with the car after a certain degree of roll angle was reached, and then "wheeee". Driving an old RX-7 was a great way to develop great opposite-lock reflexes. I cant tell you how many times I spun mine out on the autocross track.

    Tahoe, Still got that M5 rear sway bar?

    Tahoe guest

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    Sorry, sold it some time ago.
    • Member

    ND4SPDLSC

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    You should not get a significant amount of ride degradation from polyurethane anti-roll bar bushings. You may notice more squeaking if the frame to bar bushings are not greased properly. When switching to a larger bar, you may notice some increased ride harshness, but it will not be enough to outweigh the perceived performance benefit of the larger bar diameter.

    Polyurethane control arm bushings will affect ride much more though.
    • Member

    JDiazAmador

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    Does anyone know a manufacturer for polyurethane bushings that will fit the stock sway bar on the E39's?
    • Member

    shanneba

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    Power Flex shows sway bar bushings for the E39, check with Bimmerworld, VAC or BMP design online.
    • Member

    JDiazAmador

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    Thanks for the info, shanneba.

    I got the front shocks changed about two weeks ago (replaced with Sachs sport package OEM equivalents). We ended up changing the upper control arm bushings, which were cracked.

    The car feel a *lot* better now on the highway and in corners. The new shocks raised the front end of the car slightly (I was really too low anyway). So I plan to do the rear shocks soon.
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    whorse

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    The universal polyurethane swaybar bushings in the performance section at autozone fit and they are cheap!!
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    JDiazAmador

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    Whorse, I will check that out!
    • Member

    ND4SPDLSC

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    Anyone know if the Energy Suspension universal bar bushings fit? I may be swapping in an M5 front bar and a Dinan rear bar at some point.
    • Member

    JDiazAmador

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    Bushings, Sway Bars and Shocks

    My car definitely feels better with the new shocks and upper control arm bushings in the front. It makes me want to bring the whole suspension up to at least new OEM standards if not better. The car feels great in corners now. When I had the cracked control arm bushings, I felt an "imprecision" or "uncertainty" that I couldn't put my finger on.

    Power Flex seems to have polyurethane bushings for all the stock BMW sway bar diameters.

    I'd install the Dinan rear sway bar if I could get a M Sport II (25 mm) front bar. Right now I have M Sport I which I believe is Fr 24 mm / Rr 14 mm. I believe the Eibach bars are sold only as a F+R set.

    I'd be interested in purchasing your used sway bars if anyone has M Sport II or M5 sway bars that the removed as part of an upgrade. But unless they are coming from an I-6 car, I can only use the rear (I-6 and V-8 front bars are different).

    Now Bavarian Auto has a really good deal on Bilstein Sport shocks for the E39 rear. Something like $85 each. I already installed Sachs in the front (the version to match the M Sport suspension).

    What do you guys think of the combination of Sachs Sport front / Bilstein Sport rear? If the rears have stiffer damping, it might actually be beneficial since it will help control body roll and probably reduce understeer. I pretty much never have anyone riding in the back seat anyway.
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    CRKrieger

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    Shocks have only a negligible effect on body roll. Primary effect comes from springs; secondary from anti-roll bars. Shocks almost nothing.
    • Member

    JDiazAmador

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    Maybe what I'm noticing is a damping of the rate of body roll, changing from worn out old shocks to new ones.
    • Member

    CRKrieger

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    That would make sense. Although it won't ultimately change the roll angle, it could certainly stabilize the handling as it keeps it from rolling farther, and recovering from excess rolling, with good damping.

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