No announcement yet.

Weak brakes

  • Filter
  • Time
  • Show
Clear All
new posts

  • Weak brakes

    I am having a brake issue on my M3.
    I have always thought the brakes were not as good as they should be, and have trouble getting the abs to engage, even when I try to stomp the pedal hard.

    Since I have had the car, all rotors and pads were replaced and calipers completely rebuilt. System was flushed and bled with Ate super blue, and all rubber lines to the calipers and the two over the subframe have been replaced with Goodridge stainless lines.

    Fast forward to this season, and I took the car for a warm up drive around the neighbourhood to scrub any surface rust off everything, then went for a run up to grouse mountain from my house out by Seymour mountain. (about 35-40 min round trip)Got back to the house and pulled the wheels off as the brakes did not sound right to me. When I pulled the wheels off, I found the rear rotors still rusty and the fronts clean. The rear pads look almost new (after 1000 miles on the car).

    Is this an ABS pump issue or M/C issue or brake bias valve you think?
    If I bleed the rears I get fluid fine, so the line or T is not plugged, it just doesn't seem to clamp the rears very well.

    Also, my ATE m/c has a circle with a 30 in it. Is that the normal m3 m/c.
    Last edited by Jake; 07-21-2012, 05:08 AM. Reason: Got rid of the odd formatting

  • #2
    Sounds like the rear calipers are sticking, or there is insufficient hydraulic pressure to displace their pistons.
    I would exercise the rear calipers by pulling them off the hubs and check that the dust boots are intact. If the boots are intact, then w/o disconnecting the hydraulics push them in and out several times after introducing some rust penetrant and lube inside the dust boots. See if you can get them to move freely. If the boots are compromised, you'll need to rebuild or replace them.
    If they work fine during the exercise, you may need to check the functioning of the ABS unit.



    • #3
      How do I check the abs unit?

      The calipers are not sticking and have already been rebuilt.


      • #4
        Another note.
        the first pump on the brakes is a fair amount softer and longer than a second pump when braking, although not stupidly long, and it does not go to the floor.


        • #5
          I have the exact same problem and have been trying to solve it for about 2 months. The rear calipers only grab on the inside of the rotor but the outer edge of the rears is spot rusting. I have also changed the lines, rebuilt the calipers, bled about 8 times with Super blue, and just today changed put a new bias valve in. I have also put in a new booster and MC! Rear calipers slide freely, and with them off the rotors but hydraulically connected, they with engage plenty far enough by just pressing the pedal 3-4 times. I have plenty of pad and rotors are well within spec.

          My pedal feel is crisp 50% of the time and a little dull 50% of the time but never squishy or goes to the floor.

          I also have no clue what is causing the rears to not engage fully and I'm about out of things to check or replace. I have no ABS unit so I don't think that is your problem either.
          Last edited by fronton; 07-21-2012, 08:59 AM.


          • #6
            Originally posted by Todd black 88 View Post
            Another note.
            the first pump on the brakes is a fair amount softer and longer than a second pump when braking, although not stupidly long, and it does not go to the floor.
            I ran into this on a non-BMW I was working on. Problem was a loose axle nut - the hub would slightly wobble, which caused the rotor to push the pads further back in the calipers. So, the first press on the brake pedal would be long, to move the pads back out to the rotor. The next press would be OK, until you got off the brakes and drove enough to push the pads back in. Unfortunately, the wobble caused by the loose axle nut also trashed the wheel bearing and the hub, so I had to replace all the pieces.

            Anyway, just a thought...


            • #7
              Todd, are you certain that your brakes were working properly after all the work you had done? This being your first drive of the season, I thought perhaps you had all the work done before putting it away last season and are just now finding out. I ask because I am now second guessing all the work I did, particularly if I bent the new hard lines correctly.


              • #8
                The car had weak brakes since I got it. I rebuilt everything and it's still the same, no bite and next to zero rear brakes. I have never been able to get the abs to engage, no matter how hard I try.


                • #9
                  Originally posted by Todd black 88 View Post
                  Also, my ATE m/c has a circle with a 30 in it. Is that the normal m3 m/c.
                  I think that's one of your problems. The stock M/C is 23mm and even the 7 series M/C is only 25mm:

                  You've got the wrong M/C for starters.


                  • #10
                    Go buy 2 quarts of cheap dot4 brake fluid and a pressure bleeder. Put the car on jackstands and bleed it with an experienced friend until the system is properly purged. Then fill with ATE Blue only if it feels satisfactory. While the car is on jackstands (and all wheels removed), check all wheel bearings for play. If they have any amount of play, you will experience piston knock-back. Also, I think that your system is still full of air which is why you can't pressurize the rear calipers. Even if you had kept your old rear rubber lines and they had clogged shut, the MC's pressure would still be enough to push the pistons. Had you been closer to me, it would have been a pleasure to bleed your brakes with you.

                    One trick to dislodge air pockets is to smoothly pump the brakes while the fluid is already pushed by the pressure bleeder. You need some flow.
                    Last edited by LeeVuong; 07-23-2012, 04:21 AM.

                    [email protected]

                    1969 2002 racecar
                    1989 M3 racecar
                    e39 Touring


                    • #11

                      The brakes have been bled and bled and bled again, both manually and with a pressure bleeder, by myself and an experienced friend and by the local dealership, and I still cannot get the abs to engage. My e30 cab brakes are waaaaaaay better at this point.
                      i understand the "pad knock back", but it's only the first pedal application that is a little longer than the rest, no matter if I am stationary or moving. The pedal feels hard not spongy, but there is no bite and the rears are worse than the fronts it seems.


                      • #12
                        I'm not saying this is your problem but I've stopped using super blue years ago. You mention rebuilt the calipers so I wanted to mention what happened to us. I rebuilt calipers on one of our e30s using super blue bleeding every 3mo. Well it started having issues with hard brakes. Super blue attracts tons of moisture absorbing that ends up eating and corroding the internals of lines, fittings, and calipers. One car we have it completely froze the rear calipers and one front caliper. Bought all reman calipers from cardone, replaced the lines and started using prestone dot4. That was 8yrs ago. I track my M3 with prestone dot4. Don't get me wrong i'm sure super blue and others are good for application of track use but should be bled very often like every event. Even then you can expect to consider brake pads and calipers consumable items. Just my thoughts.


                        • #13
                          Hmm I did not know it absorbed water quicker than regular brake fluid.


                          • #14
                            With the engine off if you pump the brakes say 6 times hold the foot on the brakes and start the engine does the brake pedal go down, this indicates the brake booster is working as it should.

                            Are the discs and compound pads installed standard or do you have hard compound pads installed ?

                            Standard wheels and tires ?

                            ABS could be tested on some grass for lock up.

                            Stainless lines make the diagnosis harder due not able to lightly clamp the hose shut to block off the fluid flow to the caliper and test pedal feel.

                            At this stage I would not worry about the rust on the discs or the ABS unit due when the pedal problem is fixed I think these issues will solve them selves.
                            On my car the rear discs have surface rust like yours & don't clean up like the front after a run I suspect this is totally normal.


                            E30 M3 1987
                            Mini Clubman GT
                            BMW E36 323 Msport
                            Toyota Corona
                            KTM 200EXC
                            Honda CB50 (1979)


                            • #15
                              May want to clean out the rear brake press reducer. They can get gunked up pretty bad.