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Inconsistent speed independant braking vibration. 850 1996

Good day.

I have a 96 850T sedan with automatic transmission, sport suspension, and a typically shot ABS computer. Thanks ATE. I have attempted to disable the faulty ABS controller by disconnecting all ABS fuses excluding the one that makes the speedo go limp. I have also pulled the pump connector and placed it into a zip-lock, and filled in the connector with... uh... I forget... but I filled it.

My problem is that when I hit the brakes too hard, I get a nice constant vibration throughout the vehicle that is so intense that it reverberates through the car for a couple seconds after I've released the brakes. Again, the tone of the vibration DOES NOT change with the speed of the car. The tone is the same no matter what speed the car is traveling.

I think it's ABS related, but it feels so mechanical. I'm considering getting my ABS computer rebuilt, or replacing it outright. Is there anything mechanical it could be?

-Luke
--

-- Lucyen Gabbard
96 854 Turbo 90k / 86 745 GLE 240k








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    Inconsistent speed independant braking vibration. 850 1996

    If the ABS unit is disabled/disconnected and you have the vibration....
    The rear rotors are warped.
    The first time I had this problem on my 98 V70 I spent two weeks looking for the problem.
    I replaced the front rotors, pads, bled the system, disabled the ABS, replaced the rear pads and finally replaced the rear rotors, zimmerman cross drilled. Problem solved.
    Then a year later it started again, I put another set of rotors, brembo solid and no problem since.

    A defective ABS unit will cause vibration but you only feel that on the brake pedal and eventually the vibration stops and the speedometer will stop working as well.








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    Inconsistent speed independant braking vibration. 850 1996

    I can't think of any mechanically induced vibration that wouldn't be effected by speed. I think you're on the right track suspecting something you've done to the ABS especially since it only seems to happen when you brake hard. Although...... if your motor mounts are bad the motor could be shifting during hard braking. Hmmmmmm








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    Inconsistent speed independant braking vibration. 850 1996

    Most of us on this board usually send defective ABS controllers to Vic in California. About $150 to rebuild it, and it never fails again.
    http://home.earthlink.net/~vicrocha/


    If your abs is completely disconnected, I don't understand the vibration unless your rotors are warped beyound reason.

    Klaus
    --
    (V♂LV♂s 1995 854T, 1998 V70R)








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      Inconsistent speed independant braking vibration. 850 1996

      Well, after a breif experiment where I found me a hill, and got the car to start doing it by slowing from 25-40 MPH and braking somewhat hard for a few minutes, I unplugged the ABS connector, rebooted the car, and tried it again with an ABS un-damning shudder.

      I've reconnected my ABS computer and will be taking my car to the local indy to get the mechanical problem evaluated.

      So... If some fool (like me) had improperly torqued some lug nuts -- causing the rotors to warp, would retorqing them appropriately fix the problem, or is it new rotor time?

      --

      -- Lucyen Gabbard
      96 854 Turbo 90k / 86 745 GLE 240k








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        Inconsistent speed independant braking vibration. 850 1996

        Answer to retorquing lug nuts is "NO." Once rotors are warped, you can't unwarp them no matter what you do. Don't even try to turn them to fix the problem...it won't. Buy new Brembo's or Zimmerman's from www.fcpgroton.com and be done with it if your rotors are really warped. Otherwise, I would suspect a bad caliper that's sticking. Feel the tires near the brakes after a run and see if one or more of them seems excessively hot.
        --
        1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.








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    Inconsistent speed independant braking vibration. 850 1996

    The discs on these are apparently prone to warping. When we bought our 1996 and drove it in the mountains for the first time, I could get a frightening shudder after a few braking episodes - apparently, the discs would heat up and warp, causing dramatic shudders. New front discs and pads helped, though I think I may eventually need to do the same on the back.

    But this shuddering pretty well stopped when my foot came off the brake, so that may not be it. I would suspect a suspension problem.








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      Inconsistent speed independant braking vibration. 850 1996

      - to add to the Rotor issue - my rear caliper seized/stuck off and on for awhile - it would cause the odd vibration until it finally seized. When it did, the vibration was so bad I thought it was the ABS issue everyone seems to have since the whole car shaked when braking (at any speed). I guess the rotor being as warped as it was at that point, didn't help.







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