ABS problems

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  • LateFan
    R3V Elite
    • May 2013
    • 4399

    #1

    ABS problems

    My son's car has had some ABS issues and we're a bit stumped.

    The ABS light comes on often now, but pretty randomly, and sometimes before the car has even moved. When the light is on, the system is disabled as I understand it, and so does no vibrating on slippery stops. When the light is off, he says it was jerking even on dry pavement, like it wanted to work all the time when braking.

    We changed both relays on the ABS unit, as well as the one above the driver's knee near the steering column (oh, this is an '86 ES, 175k miles). We tested each corner sensor with a multi meter and got normal readings. No gunk on the teeth or sensors.

    So if the new relays haven't fixed it, are we looking at the pump? He says now he feels no jerking, but hears a hum or buzz (like from the pump??) when braking.

    What is the pump worth? Is it risky to put a good used one in?

    Thanks -
  • LateFan
    R3V Elite
    • May 2013
    • 4399

    #2
    wait a minute......$2700 new and/or NLA?? wut?

    Comment

    • E30 331is
      E30 Enthusiast
      • Sep 2011
      • 1166

      #3
      I have the same issues. Just been dealing with it. Let me know if you figure it out.

      Comment

      • Jb325is
        R3VLimited
        • Oct 2003
        • 2136

        #4
        You sure you don't have the sensors swapped left to right?
        - '88 m54 coupe

        <3

        Comment

        • LateFan
          R3V Elite
          • May 2013
          • 4399

          #5
          Don't think so - It's all original, we didn't swap any, worked fine before.

          Comment

          • Maddog
            Advanced Member
            • Dec 2006
            • 111

            #6
            When you say normal reading, are you referring to mV readings? The mV reading should increase as the wheel increases in rotation. The wheel not doing this has the faulty sensor.

            Comment

            • LateFan
              R3V Elite
              • May 2013
              • 4399

              #7
              I'll check with him on that. I remember being the wheel spinner and him checking the mV, per Bentley I think.

              Would just one wheel sensor cause this? The buzzing noise was an interesting clue. He's off at school so I'm relaying info.

              Comment

              • LateFan
                R3V Elite
                • May 2013
                • 4399

                #8
                Found some notes he made on the wheel sensors.

                Front L: .989 kΩ
                Front R: .985 kΩ

                Rear L: 1.02 kΩ
                Rear R: 1.011 kΩ

                Then I spun the wheels steady speed - as fast as you can by hand - to measure mV AC. L & R were stable and consistent.

                Teeth were OK, no gunk build-up.

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