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Z3 Rear Suspension - Side Hop

Discussion in 'E36/7 Z3 (1996-2002)' started by Philip Ross, Jun 8, 2009.

    Philip Ross guest

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    My "new" (second owner) 1996 Z3, 67k miles, does a little side-step when going down the street in a straight line, if I hit a little bump or manhole dip. Even my wife has mentioned it when she is driving by herself.

    My local wrench says it's "convertible wiggle" and that there's not enough power to wear those suspension bits out. While I am a 4 door sedan type of guy, my seat cheeks are calibrated to Hans Stuck specs and this Z3 handles like no BMW that I've driven. My wrench says his parts source doesn't keep those parts in stock, which means that folks aren't buying them, hence they aren't wearing out. Since it has the biggest engine that they put in that model that year (also the smallest and only), I beg to differ.

    I replaced both upper rear-shock mounts last year. They were torn apart.

    Someone suggested the sub-frame bushings might be the culprit. Are there other wear points in the rear suspension that should be replaced at the same time?

    What do you think?
    Phil
    Buckeye Chptr
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    tbdbitl

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    Z3 Side Hop

    Phil -

    Not sure if I can tell you how to fix it, but when I was test driving Z3s, the dealer that I was working with had several in stock - this was a few years ago. Part of the test drive was an entrance ramp to the local freeway that was concrete, and of course expansion joints. I must have driven 5 different Z3s from different years and mileage, and they would all do a sideways hop when I hit the expansion joint under acceleration.

    I later drove a Z4 (albeit a new Z4) down the same course, and got no side hop.

    I was told by the salesman that this was normal for a Z3 - the rear suspension design was older, and BMW had cured the hop in later 3 series (E46) and the Z4.

    Jerry (former Buckeye!)
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    mooseheadm5

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    Check rear subframe bushings. The power has nothing to do with them wearing out, it is just the design. They are rubber and they age and rip. Just because Worldpac doesn't stock something doesn't mean there is no market for it.
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    steven s

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    Some of this is inherent it the Z3 (as well as the 318ti which share the same rear suspension). As stated, subframe bushings are a good place to start. Also look at the trailing arm bushings. I kinda like the hop. :D

    willconltd guest

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    While the Z3 does use a semi-trailing arm package, there was a real weak point in the sub-frame busings on the Z3. Replacing them with Urethane bushings goes a long way to settling the rear end so you don't get all those wiggles.

    The stock subframe bushings were so poor that you could manually move the whole subframe around by hand with the car on a lift. In this photo, you can see that they are hollow bushings. I estimate they could deflect by 1-2 inches in normal driving. I also think this added to the sub-frame issues experienced by a few Z3 owners.

    Ireland Engineering came out with a bushing replacement pretty early in the life of the car that resolved this issue.

    You can see in this picture that the sub-frame bushings are hollow.

    [IMG]

    [IMG]

    Its a must have for any Z3. They also make stiffer race style bushings, but I think these are unnecessary for a regular use car.

    http://store.nexternal.com/shared/StoreFront/default.asp?CS=ireland&StoreType=BtoC&Count1=251461207&Count2=168601632
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    steven s

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    Polyurethane is only going to increase the hop since it is less compliant.
    I went that root. If I need to replace my bushings again I'm going back to stock.

    willconltd guest

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    What bushings did you use?

    My experience is that the rear sub-frame moves too much with the stock bushings, not too little.
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    bcweir

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    Urethane will behave differently than the stock rubber bushings.

    Urethane bushings were not originally designed for street use, as they don't compress or expand the way rubber bushings do. They're designed to be more rigid and harder, and instead of absorbing the energy from bumps and impacts, they dissipate it through the rest of your car's structure.

    For this reason, they're not recommended for regular street use (at least not by people who are not trying to sell them to you).

    The difference between a glass smooth racetrack and most public streets and highways will seem like night and day to a urethane bushing.

    If BMW had thought urethane was superior to rubber in terms of performance, urethane likely would have been an OEM install. Price would not have been a concern, since as a volume buyer, BMW could have certainly fought for and gotten a price similar to or cheaper than rubber.

    If you want to retain the factory ride and behavior, get the factory replacement rubber, not the cheap Chinese bushings. Those are made of an inferior grade rubber that while cheaper, will not hold up for very long. Don't be surprised if you find yourself replacing these cheap Chinese parts in another six months.

    willconltd guest

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    The bushings I reference are not Chinese made, but are hand made right here in America by Ireland Engineering. I do not recommend the Orange or track Urethane bushings as they can be too harsh, but the IE "Green" bushings were designed specifically for the Z3 in a normal non track driving environment.

    The initial concern was the play in the sub-frame, which the Green bushings make a dramatic difference. This is especially a night and day difference when exiting a decreasing radius off ramp. They eliminate the rear end wiggle that is rather unsettling in regular driving.

    In this specific case, the factory rubber is far inferior to the IE bushings because they allow far too much play in the rear end. This becomes much more pronounced with the M cars.

    So while I may agree with your sentiment that buying cheap bushings off Ebay is a bad idea because you don't know what quality you are getting, the IE bushings are an upgrade that BMW should have done from the factory.

    This is the first time I have heard anyone speak negatively about these bushings, and I can only assume they didn't get the IE Green bushings or more than likely Steven doesn't have a Z3 and is generalizing from his Ti with an engine swap.

    The difference is night and day, and anyone who has done it on the Z3 can tell the difference in taming the rear end wiggle.

    All of this being said, not replacing the bushings may also be a cause of the differential mount tearing away from the trunk floor, but thats probably just my opinion, but my opinion on Z3s means something.
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    steven s

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    I have Ireland's. Subframe and rear trailing arm bushings.
    Like I said. I would not do it again.

    I recall a crest in the road that my car always stepped out a bit.
    After installing the polyurethane, the twitch was even more pronounced.

    It is works for you, great. It does not work for me.
    My ti serves as my daily driver in the spring/summer and sees about 3 or 4 weekends]on track.

    willconltd guest

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    Well, rather than try and argue with you, I find that you are trying to apply your experiences with a 318ti with a swapped motor to a Z3. First, they do share the same basic rear suspension design, but the geometry is different for the Z3. Its a popular upgrade to the TI, but its not the same. Also, I would estimate that a 328Ti would weigh somewhere over 3000 lbs and have a completely different center of gravity than the Z3. The Z3 has the entire driver cabin shifted back approximately 14 inches over the other E36 cars. So your experiences probably with your Ti probably do not apply to the Z3.

    Rather than try and argue with a Non-Z3 owner, I will suggest that someone looking to resolve this issue do a search is the Z3 forum over at Bimmerfest. Its by far the most knowledgeable place on the internet when referring to Z3 issues.

    http://www.bimmerfest.com/forums/forumdisplay.php?f=7

    Most people who do the trailing arm bushings or who add the adjustable trailing arm bushings are dissatisfied with their performance. I have never met anyone who has had negative opinions of the IE Subframe bushings. Everyone I know who has a M Z3 has the IE bushings installed in their cars.

    Whenever someone makes a list of the best Mods for the Z3, IE bushings are usually in the top 3.
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    steven s

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    That's true. It's not an accurate comparison.
    It's only my experience with my car.

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