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    variable spongy brakes

    I recently rebuilt my calipers (a job I've done before), put in new pads, and did a brake fluid flush. I did this in part because it's a new track season, and also because I had a spongier brake than I was comfortable with. When I was done the brakes felt less grippy, so I bedded them in and got my grip back and stopping power back. But the variable sponge was still there.

    After doing some research my conclusion was that if a gentle press of the brakes causes the brake pedal to drop significantly further than stabbing the brakes, that there was either a leak or the brake MC was bad. Since I track my car I watch my brake fluid level like a hawk. I also did a visual inspection and came up (literally) dry. Brake MC it must be!

    So I replaced the brake MC, flushed the entire system again including the clutch, and....still spongy. If I stab it I still get a very different pedal feel and travel than if I ease into them. So what, after two flushes, and a new MC could cause this? Air in the lines? Note that I use a pressurized system to push the fluid through the lines. I feel confident I'm doing this as best I can, or at least as best as I've done the previous 10 brake bleed jobs and all of them were successful.

    Here is the last tricky bit, and my current suspicion. I might have air in my ABS unit, but without functional ABS I can't force the unit to activate. Since it's a track and dry weather car with aspirations of being a Pro3 car, I'm tempted to just bypass the ABS unit all together and make my like simpler. It's never worked and I have no intentions of spending the time/money to make it work.

    Thoughts? Other suggestions? Anyone had this before? Maybe I'll post a video demonstrating the difference in the pedal.
    -------------------------------------------------
    1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
    2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

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    I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

    #2
    I have the exact same problem actually and I'm quite fed up with it; there is a way to cycle the valves in the ABS unit (the dealer should be able to do it iirc) but I'm not sure what it entails.
    paint sucks

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      #3
      Just looked into it. Read through this thread a bit: http://www.r3vlimited.com/board/showthread.php?t=251112
      paint sucks

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        #4
        I just read through that thread, and sadly by the end the fix was to replace the shoddy "OEM equivalent" pads with a better pad. I'm running PF06 front and back, and before that HP+. And in either case a pad shouldn't cause the pedal to feel different depending on the quickness with which it is depressed.

        I had not tried bleeding while tapping on the ABS unit though. Maybe that'll loosen some air up...
        -------------------------------------------------
        1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
        2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

        sigpic

        I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

        Comment


          #5
          Yeah unfortunately there doesn't seem to be a definitive answer for you. If I were you I would try and bypass the ABS to tell if that was the problem. I haven't yet replaced my master cylinder, so I'm not yet to that point.
          paint sucks

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            #6
            Originally posted by Earendil View Post
            I just read through that thread, and sadly by the end the fix was to replace the shoddy "OEM equivalent" pads with a better pad. I'm running PF06 front and back, and before that HP+. And in either case a pad shouldn't cause the pedal to feel different depending on the quickness with which it is depressed.

            I had not tried bleeding while tapping on the ABS unit though. Maybe that'll loosen some air up...
            it shouldn't.. but it can! however in your case, both the PF06 and HP+ are good pads so you must have an issue somewhere else, like air in the lines.

            Try tapping the calipers with a wrench while you bleed them. I tend to get a lot more air bubbles out that way.
            Build thread

            Bimmerlabs

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              #7
              I have this issue as well, but only occasionally. I drove my car in the snow and activated the ABS a few times, that seemed to make it worse. Eventually I'm probably going to remove the ABS and replace the master. If that doesn't work, I'll sell the damn car. Haha.

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                #8
                I just pulled my master and checked it out and there are no fluid leaks externally; I am hesitant about just replacing it now as I don't just want to throw money at the problem.

                I have bled my brakes probably 6 times since going to the E32 master for the 24V swap, at least 2 of those were full system bleeds, and yes I tapped the calipers with a wrench during the bleed in an attempt to get the air out. Either my master cylinder failed internally in some uncommon way, or there is somehow still air trapped somewhere. I'm looking into options to bypass the ABS temporarily.
                paint sucks

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                  #9
                  I'm in the same boat as you, and sometimes the clutch pedal does the same thing, I can't drive the car if I can't shift:(

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