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Left Front Brake Caliper Issue

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  • Left Front Brake Caliper Issue

    1990 M3, car was pulling to the right under braking. I knew the right front caliper had been rebuilt and I had a kit for the left front. Additionally the RF wheel would be warm and the LF cool after a drive. With the caliper rebuild complete I figured I should bleed out the nasty old fluid before bolting up the clean caliper. Set up a catch bottle and stepped on the brake. Oddly, I had a firm pedal and no fluid went in the catch bottle. Also realized that fluid did not readily drip from the line while the caliper was off. Detached flex hose and blew compressed air through: clear. Detached hard line from ABS, blew air, clear.

    Do I need to have the caliper attached in order for fluid to flow from the ABS control unit? I'm thinking that my LF caliper was not receiving fluid pressure and that is why the car pulled right.

    Do you have any recommendations where I should look next? What can I test or clean?


  • #2
    the valve inside the ABS that controls left front is stuck in a closed position.
    Safest way to try and free it up would be by using the BOSCH ABS 2 LED tester but few german brand garages would still have them.

    Another way is to apply 12 V to the appropriate pin below the black cover on the ABS unit itself.
    See here for detailed description

    Shadetree mechanic's way would be to put it all back together and find a quiet stretch of Gravel road and do whilst nobody is driving behind you some emergency stops from 20mph to stand still. Car will pull to the right so be aware and start at low speed to get a feel for it.


    • DadsM3
      DadsM3 commented
      Editing a comment
      Thank you for this recommendation. I ended up replacing the ABS unit.

  • #3
    I ended up posting this question on the S14 Facebook group as well. I want to thank the group for responding to my question and recommending Jordan Sarette and for my ABS issue. Jordan responded right away, shipped a rebuilt ABS module, and answered my questions along the way. The rebuilt unit is beautiful and works well.​