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Thread: Fishtailing rear end

  1. #1
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    Fishtailing rear end

    I have a 2000 M Roadster with 54,000 miles on it. Tires are new Michelin Pilot Super Sport. When driving normally, on a straight road, the rear end of the car starts fishtailing at around 50 - 60 mph and seems to get worse as speed increases. Steering doesn't seem to be affected but the fishtailing is violently felt in both driver and passenger seats. I don't see any evidence of rear subframe separation...the spot welds in the trunk floor look good.
    I'm not sure what to look for and will appreciate any help in diagnosing this problem.

  2. #2
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    Did it do it before the tyres were fitted?

  3. #3
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    My 99 coupe would tramline terribly, frightening in the wet over 40 mph.Still not sure why.

  4. #4
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    When was the last time you had the suspension aligned?

    I have a '98 M with the same tires. I had some rear tramlining yesterday over some tar seams in the road where the rear wiggled a bit, but that was at 25 MPH. If you are having that happen at 60, you need to see what's up with the rear end.

    Have you replaced the rear shock mounts yet?

    1998 M Roadster, Dinan Stage 3/M50 intake, Ground Control 500# coilover suspension, 3.73 diff


  5. #5
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    Yes, but maybe not as noticeable. I have put on only a few hundred miles with new tires.

    - - - Updated - - -

    Suspension was aligned when new tires were installed...maybe 300 miles ago. I have not yet replaced rear shock mounts... as far as I know suspension is all original.

  6. #6
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    How many miles on the suspension? Assuming it's all 16-17 years old, you may be seeing the results of grippier tires pulling at worn out points. When I bought mine the rear shocks were shot (at 109K miles) and at a certain speed the rear end had a rotory sensation, sort of like J.Lo walking down the street. New RSMs and shocks (among other things) solved the problem.

    1998 M Roadster, Dinan Stage 3/M50 intake, Ground Control 500# coilover suspension, 3.73 diff


  7. #7
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    Quote Originally Posted by Telecomtodd View Post
    How many miles on the suspension? Assuming it's all 16-17 years old, you may be seeing the results of grippier tires pulling at worn out points. When I bought mine the rear shocks were shot (at 109K miles) and at a certain speed the rear end had a rotory sensation, sort of like J.Lo walking down the street. New RSMs and shocks (among other things) solved the problem.
    If that kind of expense is necessary to correct a J.Lo sashay...how much would it cost if the rear action resembles that of Nicki Minaj?

  8. #8
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    Beacoup dollah, boyyyyyy.

    rear_zpsrhkogcsb.jpg

    1998 M Roadster, Dinan Stage 3/M50 intake, Ground Control 500# coilover suspension, 3.73 diff


  9. #9
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    I'm crying here, stop it!



    Two (2) points: brand new tires definitely have tread squirm, from the tall tread blocks, and I very recently replaced the shocks on a 37,000 mile virgin '99 Coupe and they were totally shot__virtually no resistance whatsoever to compress/extend their shafts (they had been used for an undetermined amount of time with H&R springs).

    In the past, I've publicly stated that the OE M shocks were toast by 42,000 miles (amazes me the number of cars I see with excess of 100k on original suspensions ); I think it's time to revise that number downward! Konis are my recommendation: good ride and xlnt control.

  10. #10
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    slightly OT but will original shocks show as SACHS on the tube? I was under the 137k 2.8 roadster i just purchased and they looked pretty untouched.
    13 Grand Cherokee Limited V8 - Daily Driver - Wife
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  11. #11
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    Before you even get into all of that, have you looked at the most simple causes of vibration?

    I know the OP said "fishtailing," but is it truly fishtailing, meaning the back end does not maintain traction, or does it just feel "loose?"

    Bent wheels first, then alignment. Depending on what is found in the alignment, bent suspension arms or needs bushings or mounts.

    Original bushings on a 17 year old car will be in need of replacement. Rubber ages, no matter the storage conditions or mileage.

  12. #12
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    Can you post your alignment specs?
    -Abel

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  13. #13
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    Quote Originally Posted by 328 Power 04 View Post
    Can you post your alignment specs?
    Data is always a good place to start...

    wondering if he's ended up with a bent trailing arm and has a toe or asymmetric camber problem.

    - - - Updated - - -

    Quote Originally Posted by lpschafer View Post
    I have a 2000 M Roadster with 54,000 miles on it. Tires are new Michelin Pilot Super Sport. When driving normally, on a straight road, the rear end of the car starts fishtailing at around 50 - 60 mph and seems to get worse as speed increases. Steering doesn't seem to be affected but the fishtailing is violently felt in both driver and passenger seats. I don't see any evidence of rear subframe separation...the spot welds in the trunk floor look good.
    I'm not sure what to look for and will appreciate any help in diagnosing this problem.
    When you're sitting at a standstill - engine off - but key in and turned so the steering wheel is unlocked: how much play do you have in the steering wheel at the rim? None? Small fraction of an inch? Or you can rock the wheel back and forth more than a fraction of an inch? ... what I'm thinking, is that you might have a lower steering column flex disc that's gone, a steering box that's gotten loose, or a rod end that's become likewise? ... I'm assuming that when you say fishtailing, that you're not actually losing traction in the rear, but the car is wandering left then right then left etc... that can be caused by asymmetric alignment front or rear, or by loose steering system components.

  14. #14
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    Quote Originally Posted by Randy Forbes View Post
    (amazes me the number of cars I see with excess of 100k on original suspensions );
    Sorry (180k miles, bought about a year ago). I swear the reason I'm just finishing replacing mine is because everything else is also old! (maybe also because I totaled it and had to get it rebuilt).

    Too bad you probably don't have a frame alignment machine, I'd make a trip to FL for someone I could trust.

  15. #15
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    Quote Originally Posted by LannVouivre View Post
    Sorry (180k miles, bought about a year ago). I swear the reason I'm just finishing replacing mine is because everything else is also old! (maybe also because I totaled it and had to get it rebuilt).

    Too bad you probably don't have a frame alignment machine, I'd make a trip to FL for someone I could trust.
    For some perverse reason, I wish I did have a frame alignment rack!

    Not so much to un-pretzelize a car/chassis, but for the sake of alignment checking. Could you imagine some future purchaser of my house/shop, wondering why there's a 5' x 12' x 1' (preferably Starrett) granite slab in the garage...

    If only those things were free

  16. #16
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    Quote Originally Posted by Randy Forbes View Post
    Could you imagine some future purchaser of my house/shop, wondering why there's a 5' x 12' x 1' (preferably Starrett) granite slab in the garage...
    "Incomplete bomb shelter," or, "I got it for free from a dumpster," or, "I'm *really* in to metamorphic rocks..." I suspect any of those would fly better than, "I did automotive body repair out of my garage." I think a lot of people are a bit touchy about "amateur" (you're a professional) auto repair.

  17. #17
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    Incomplete bomb shelter...found one of them in St. Louis in the basement of a house we were looking at. Looked up at the ceiling and could see the paint had lightly covered "fabric". What kind of "fabric" would you put in a bomb shelter built in the 50s? Asbestos, of course! Passed up that deal...

    1998 M Roadster, Dinan Stage 3/M50 intake, Ground Control 500# coilover suspension, 3.73 diff


  18. #18
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    Quote Originally Posted by Telecomtodd View Post
    How many miles on the suspension? Assuming it's all 16-17 years old, you may be seeing the results of grippier tires pulling at worn out points. When I bought mine the rear shocks were shot (at 109K miles) and at a certain speed the rear end had a rotory sensation, sort of like J.Lo walking down the street. New RSMs and shocks (among other things) solved the problem.
    any pics or vids of that JLo stuff?.......lol

  19. #19
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    Quote Originally Posted by lpschafer View Post
    Yes, but maybe not as noticeable. I have put on only a few hundred miles with new tires.

    - - - Updated - - -

    Suspension was aligned when new tires were installed...maybe 300 miles ago. I have not yet replaced rear shock mounts... as far as I know suspension is all original.
    Maybe you got a bad alignment?

    If you were happy with how it drove and they changed the alignment, then it is going to drive differently afterwards (either better or worse). Did you get the before and after alignment specs?

  20. #20
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    Quote Originally Posted by jrkoupe View Post
    any pics or vids of that JLo stuff?.......lol
    butt%u0025252520car_crop.jpg

    1998 M Roadster, Dinan Stage 3/M50 intake, Ground Control 500# coilover suspension, 3.73 diff


  21. #21
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    Sorry this has taken so long...I've been away from home. Here are alignment specs:
    Left Front: Camber = -1.0 Caster = 7.1 Toe = 0.16
    Right Front: Camber = -0.9 Caster = 7.7 Toe = 0.17
    Left Rear: Camber = -1.6 Toe = 0.88
    Right Rear: Camber = -1.1 Toe = 0.23

  22. #22
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    your rears are kinda not equal?????????........that could be fishy...no pun intended

    look how equal your frts are.......

  23. #23
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    Fishtailing rear end

    Total toe and cross Toe looks outa wack.
    But how are your rear control arm bushings?


    Sent from my iPhone using Tapatalk

  24. #24
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    Subframe bushings? My 98 Z3M, with 90k on original SF bushings, did some odd moves over uneven pavement. With IE subframe bushings, it didn't do that anymore. I hadn't realized how bad it was until I felt the new bushings. The manners of the car got better in every way. It feels like the rear tires now follow the front tires, like they are supposed to. I think every Z3 should have IE subframe bushings.

  25. #25
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    Quote Originally Posted by LannVouivre View Post
    "Incomplete bomb shelter," or, "I got it for free from a dumpster," or, "I'm *really* in to metamorphic rocks..." I suspect any of those would fly better than, "I did automotive body repair out of my garage." I think a lot of people are a bit touchy about "amateur" (you're a professional) auto repair.
    Ahh, see, there is a fatal flaw in your logic... you see, my friend, granite is an igneous rock, not metamorphic...

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