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Thread: Brake Pedal Feel Issue

  1. #1
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    Brake Pedal Feel Issue

    1999 M3 had terrible brake pedal feel. Replaced the booster with a brand new unit in hope of fixing the issue. During replacement master and ABS unit were both completely removed and essentially dry of any fluid.

    After everything was back together I extensively bled using both the traditional 2 man method and power bleeder. Drove the car around, activated the ABS and rebled. Pedal gets hard after a few pumps while the ignition is off but when the ignition is on the pedal feels like crap - several inches of play in which the brakes do essentially nothing. The brakes "work" in that once I get past the first few inches of mush the car stops but the pedal feel is killing me.

    Ive now bled the car many times pushing many litres of fluid through it. No bubbles come out anywhere. I've tried various tricks I've read about to activate the ABS/ASC while on jackstands (in addition to driving it to activate ABS) and nothing seems to help.

    I also tried using a MittyVac but after pulling a vacuum and opening the bleeder, it seemed like relatively little fluid came out. Could this be indicative that there's a problem? Should the MittyVac bleed tube fill completely with fluid or should it slowlyish trickle out?

    Any ideas/suggestions before I take it to the dealer in hopes that putting the ABS into bleed mode will solve the issue? Sorry for the long thread and thanks in advance, this problem is driving me crazy.

    UPDATE: Car bled by dealer - no change whatsoever in pedal feel...
    Last edited by VengeanceM3; 12-30-2008 at 12:54 AM.

  2. #2
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    This is still likely a booster issue since the MC pumps up well when the booster is inactive. Most likely you need to adjust the length of the rod that activates the booster and MC. Were these all original to the car, or could they possibly have been messed with? I made mine feel a lot better by making this adjustment. Just be careful you don't make the shaft too long and prevent the booster from releasing.

  3. #3
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    Endoforce5, good suggestion, but are you sure e36 has an adjustable rod for the booster, i thought it was the e30 which had the adjustment?

  4. #4
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    Sorry, I'm not sure about which BMW's are adjustable. I have not had this problem with my BMW's. My experience was on an acura based system. You may have to modify the factory rod if it is not adjustable. Sometimes the factory tolerances stack up in your favor and sometimes they don't.

  5. #5
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    Nope, e36 booster does not have an adjustable pushrod unfortunately.

    Any other ideas? I had the car bled at the dealer today to no avail so I guess that rules out air in the system...

    Any tests/things I can look at to really rule out potential causes of the problem? Any help would be greatly appreciated.
    Last edited by VengeanceM3; 12-30-2008 at 01:56 AM.

  6. #6
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    Could be something with the brake lines...

  7. #7
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    What pads and have you used them on the track?


  8. #8
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    Quote Originally Posted by VengeanceM3 View Post
    Pedal gets hard after a few pumps while the ignition is off but when the ignition is on the pedal feels like crap - several inches of play in which the brakes do essentially nothing.
    If the pedal gets firm when the ignition is off, it's not the master. The fact that the pedal gets mushy when the ignition is on points to something that works only when the car is on: booster or ABS unit.

    When the ignition is on, does pumping the pedal make it firmer? (consistent pedal feel) If not, there's no air in the system.

  9. #9
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    Thanks for the help guys.

    Pads are PFC-Z with 5 DE days but have ~50% left still.

    Pedal does firm up with ignition off but with ignition on pumping does not make the pedal more firm.

    And when I say the pedal is spongey I'm talking 2-3" before the pedal has any firmness.

  10. #10
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    Sometimes caliper retraction can be an issue too. You might try new pads or pad spacers to reduce the travel to the rotors when the calipers retract. A spacer between the MC "input shaft" and the booster may also help. I'm sorry I don't have the link handy but you could do a google search to learn the basics of how a brake booster system works. The info is certainly there. The tolerances in the stock system can have a great effect on feel.

  11. #11
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    Thanks, Ill have to throw some new pads in and see if that helps.
    Could this be an issue at the calipers? Anyway to tell if a caliper needs to be rebuilt?

  12. #12
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    We experienced similar issues a few years ago when we changed types of brake fluid from one high temperature brand to another. Evidently, something involved in the swap (when the two mixed) inside the master cylinder damaged the seal(s) just enough for them to have fluid bypass when ignition was on despite feeling pretty firm when vehicle wasn't running. We chased the spongy pedal with repeated bleeding, ABS activation, checking of calipers, pads, lines, etc to no avail. Found no bubbles when we bled. Ran liters of fluid through the system so that everything seemed normal....except that the pedal feel was awful when the power brake system was powered-up. Replaced the brand-new master cylinder with another brand-new master cylinder (this one was only in contact with the second brand of high-temp brake fluid) and once we got all of the subsequent bleeding done the problem was solved. Close inspection of the first brand-new master showed absolutely no signs of damage or failure....but it was obviously the culprit. I have direct knowledge of others experiencing similar master cylinder failure issues when switching brands of high-temp brake fluids (most notably when one of them was ATE's version).

    So, given the relatively low price of a new master cylinder compared to the angst of continuing to chase this particular demon, I'd give that a try based on my personal experience of it being the unexpected solution.

    Good luck.

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  13. #13
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    Bring this one back...

    Can anyone who thinks they have fixed this either via a new MC or new booster measure the pedal travel needed to get past the "mush"?

    With the car off, my pedal travels 2" before it pretty much stops and I feel like I would then be really hard on the brakes.

    With the car running, it goes 2.75" to get to the same feeling.

    But that extra 3/4" makes it tough to heel/toe.

    Just wondering if the people who have had this problem had some crazy amount of travel that replacing the booster or MC fixed.

    Or to ask another way, how long is the "long pedal" we are all trying to fix?

    FWIW, I have changed both my MC and booster, and bled, and bled, and bled.

    I guess I am thinking I want the car to feel like it does with the engine off when it is on, which feels about perfect.

    Matt
    1994 325is Spec3

  14. #14
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    FWIW, Ive now changed the master, booster, abs pump, SS lines, all 4 calipers are rebuilt with SS pistons and solid guides, and ive pushed countless liters of fluid though it all, including every trick Ive read to flush the ABS of air. Pedal still feels pretty terrible on the street - though with the PFC-06 pads I threw on at the track, it certainly has no problem stopping and is actually setup quite well for heel-toe. I can try to measure the pedal travel later today or tomorrow.
    Last edited by VengeanceM3; 05-17-2009 at 11:37 AM.

  15. #15
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    What pads are you using on the street? Have you tried another set during this process?


  16. #16
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  17. #17
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    Sounds exactly like the issue I have with my 99 e36 323is...It's a mushy feeling, I can actually press the pedal all the way down to the floor with EASE when i'm driving(the thing still brakes hard though) I have only 8k miles on brembo oem replacements and hawk hps pads.

    I'm actually going to change my brake lines to SS lines soon. From what i've read in this thread and elsewhere it sounds like the brake lines have expanded over the years and there is not alot of pressure in the lines.

  18. #18
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    Quote Originally Posted by Le Nitro View Post
    Sounds exactly like the issue I have with my 99 e36 323is...It's a mushy feeling, I can actually press the pedal all the way down to the floor with EASE when i'm driving(the thing still brakes hard though) I have only 8k miles on brembo oem replacements and hawk hps pads.

    I'm actually going to change my brake lines to SS lines soon. From what i've read in this thread and elsewhere it sounds like the brake lines have expanded over the years and there is not alot of pressure in the lines.
    I went the brake line route and the pedal is still mushy The only thing that helped "slightly" are Axxiss ultimates. The mushiness is not gone but at least the brake grabs faster.

    I may try the MC next...
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  19. #19
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    check your wheel bearings... if they be bad, the rotor could be pushing the pistons back into the caliper.

    If you really want good pedal, feel dump the booster and install a dual master setup. It's a LOTTA WORK, but it's only way to go get proper pedal feel.
    like2short
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  20. #20
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    Quote Originally Posted by matt325 View Post
    Bring this one back...

    Can anyone who thinks they have fixed this either via a new MC or new booster measure the pedal travel needed to get past the "mush"?

    With the car off, my pedal travels 2" before it pretty much stops and I feel like I would then be really hard on the brakes.

    With the car running, it goes 2.75" to get to the same feeling.

    But that extra 3/4" makes it tough to heel/toe.
    I guess I am thinking I want the car to feel like it does with the engine off when it is on, which feels about perfect.
    Add another. I've got the same issues. Also affects HnT. In my case it shows up about one lap in on a run, once I've used the brakes hard once or twice. Brake is firm when off.

    Starting to sound like this is just a semi-common E36 issue. I've thrown enough good money after bad with this car over 12 years that I may just live with this rather than try changing one expensive component after another.

  21. #21
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    Unfortunately its an e36 thing. I had the same problem when I was running stock brakes and was only temporarily resolved with new pads. But once the pads were down to 50/60% the pedal would fall below the plane of the gas pedal and be firmly spongy. Nothing bleeding could resolve. My abs, brake master and booster are 148k miles old.

    All these problems went away when I upgraded the brakes to big brakes. Always firm and consistent lap after lap.

  22. #22
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    Fatigued calipers?
    Craig Brickner
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  23. #23
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    Quote Originally Posted by TIATO View Post
    All these problems went away when I upgraded the brakes to big brakes. Always firm and consistent lap after lap.
    same here except when the pads get low (under 25% left), then the brake pedal gets soft again

  24. #24
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    Quote Originally Posted by Car54 View Post
    Fatigued calipers?
    What do you mean by "fatigued?" I have a new MC (and reservoir), new stainless lines, all rebuilt calipers, fresh fluid, and I still get the sinking pedal. It's certainly not as bad as what's being described here, but the hydraulic boosted systems in my E28s always felt much better on track, fixed calipers (M5) or floating (535). I haven't replaced the booster, but I have done the vacuum line. Wheel bearings are all new (last season). Nothing I did ever really affected braking performance; the MC marginally improved feel.

    My symptom is generally longer travel than I'd like (a good bedding of the pads does help that, but heel/toe is still not as easy as it was in my E28s), and an *occasional* sinking pedal. It seems to happen at almost random spots, but it's repeatable. For instance, at Mid-Ohio the pedal seems funny braking before T12 (right-hander before Thunder Valley) nearly every time through, but it's good on most of the track. No idea what would be different about that spot.

    When the pedal sinks, the car still slows perfectly well. I have pretty much given up on it. $400 for a booster is a lot of money to throw at it just to "see if it works." Maybe next winter I'll change it, but as long as the car can haul down effectively, I can deal with a funky pedal from time to time. If anyone can give a rational, valid explanation of what component (booster or ABS pump are the only two left!) could cause this behavior, then I'll replace the parts. It's not pad knock-back unless brand-new wheel bearings have too much play or rotors are excessively out of true (no shimmies or shakes, though). It's not the MC unless I and everyone else has had an out-of-box failure (I'd believe one person in this forum did, but not everyone who replaced the master). It's not sticky calipers--when I rebuilt mine I replaced guide pin bushings, guide pins, and the rubber parts, and had no visible wear inside the rotor. I get even pad and rotor wear and no pulling under braking. It's not the brake lines, unless my brand new ones are somehow compromised. There is no fluid loss.

    So, either calipers can wear out in a way that I'm completely unaware of, or the booster is the issue, or the ABS pump somehow is affecting things (even when I don't engage the ABS?). I'd love to know. As is, my system works, it just lacks feel. The only consistent answer I've heard is that "fixed calipers cure the problem." Well, for classing reasons that's not an option.

    -tammer

  25. #25
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    Maybe it's just the MC design/size problem. Are there any other (maybe bigger) MC that could fit into an E36?

    It seems like if MC can pump out quicker, then the calipers will grip sooner and the pedal will reach the firmer state sooner.

    Are there any bigger size BMW MC that will mate with an E36 booster?
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