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Thread: Brake Pedal Feel Issue

  1. #76
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    Bumping this up to see if anybody has discovered a solution to nasty pedal feel in the E36.

    Quote Originally Posted by tammer View Post
    Rock hard when sitting still with car off. Soft when the car is started (booster engaged). Soft when braking with high vacuum (off-throttle), harder when braking at full throttle (left foot). Braking performance is good no matter what--no fade, no pulling. Pedal consistency (travel and feel) is the issue.

    Quick recap ... New MC, soft lines (SS), rotors, pads (multiple sets), wheel bearings. Rebuilt calipers.

    -tammer
    tammer has described exactly my problem. In chasing it I moved to a UUC/Wilwood brake kit / braided steel lines (four wheel) and pedal feel has improved somewhat, but still not anywhere near what is desired. I have had the car bled by the dealer to no avail, I've pushed endless fluid through it using many techniques (foot, vacuum, pressure…). Regardless of pad selection the pedal just won't firm up. Feels as though the first 2-3 inches is a sponge and after you get past that there is some nice firmness to be had.

    I've not gone about replacing the master cylinder yet, which I suppose I could do. Would be happy to disconnect ABS entirely if it would help. Wheel bearings are new on all four corners.

    Ideas? Thoughts?
    Last edited by Evil Spoonman; 12-14-2009 at 12:46 PM.
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  2. #77
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    I'm currently running M3 brakes with the 328 MS with similar results. Bled the brakes at least 3 times, checked to see if the system holds pressure (which it does), booster is good, and I just recently replaced the check valve and seal at the booster since I suspected a vacuum leak.

    Since the brake system was completely dry at one point I'm going to bleed it again after winter. If things aren't good enough then I will make a custom line so I can install my M3 MS.

  3. #78
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    Someone mentioned caliper return issues, and I agree. Particularly with Hawk pads on the rears, there is a spring clip arrangement that is supposed to attach to the caliper piston allowing the pad to be subject to both in and out movement of the piston. If you install the pads without clipping that spring around the caliper piston, excessive space is created and a couple of pumps are required to take up the slop. I have seen this in E-36s and Minis. Check rear pad installation and be certain the spring clip on the pad clips around the caliper piston. I agree with others you do not have a booster, master or caliper problem though it is necessary to get full command of the abs through computer operation to bleed properly. You can order the software from Autoengineuity for a lap top and it comes with cabling to go to the OBD connector.

    Good luck.

  4. #79
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    I have a 94 325i Spec 3 and experienced all of these rather annoying symptoms. In an effort to increase feel and maintain a firmer pedal, I had the Mc and booster replaced. Although it helped some, it by no means solved the problem. The motor makes plenty of vacuum so I know it is not that problem. According to my far more imformed shop (James Mus, you're the man) it is a symptom of the design. In the E30's, there is some adjustment to aid the driver, in the E36, BMW removed this functionality.

    The only "solution" I have found for major braking zones, turn 1 at Summit and VIR for instance, is to not just tap the brakes to set the pads, but rather to press just a little bit further than "pad set" in an effort to push as much fluid into the system, then lift the pedal, thus refilling the MC. Then after that is all done, crush the pedal to stop the car.

    Yes, it sounds like a lot, but you can accomplish it rather quickly and have a pedal which is much nicer to work with in threshold situations.

  5. #80
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    I too have been working with this problem for months. I track a 94 325 with a brake pedal that feels like a nice pillow. Like all the others, I've bled countless time and racked my brain. I am about to replace the master cylinder after reading the post from Akard on the first page of this thread. I'll also replace the pads and examine the current PFC 01's (?) that i have in there for pad taper.

    I dont want to resign the problem to a "design flaw", as i know that other cars exactly like ours do not suffer from this issue. Let's get this problem solved.

    Thanks all for the research already done before i got here.

    Adham

  6. #81
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    Quote Originally Posted by jonmacs22 View Post
    The only "solution" I have found for major braking zones, turn 1 at Summit and VIR for instance, is to not just tap the brakes to set the pads, but rather to press just a little bit further than "pad set" in an effort to push as much fluid into the system, then lift the pedal, thus refilling the MC. Then after that is all done, crush the pedal to stop the car.

    Yes, it sounds like a lot, but you can accomplish it rather quickly and have a pedal which is much nicer to work with in threshold situations.
    So far, this is the only thing that's helped me as well. Left-foot press/release before nailing the brake.

    Still, if there is a definitive cure, I'd love to know.

    -tammer

  7. #82
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    Quote Originally Posted by tammer View Post
    So far, this is the only thing that's helped me as well. Left-foot press/release before nailing the brake.

    Still, if there is a definitive cure, I'd love to know.

    -tammer
    Somewhere on VHS tape I have some foot-camera video of Ricky Rudd at Sears Point. Coming into T11 (high speed run into tight hairpin) he did about three quick left foot pumps before going into hard braking and heel toe.

  8. #83
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    Speaking logically we can eliminate a few things:

    - Hard lines
    - Flexible lines
    - Calipers
    - Pedal geometry
    - Brake fluid type/bleed method
    - Pad selection


    What remains as part of the system?

    - ABS and its associated lines and hardware
    - Master cylinder
    - Booster


    So lets start eliminating the rest:
    - Does removing ABS cure the problem? Anybody with ABS entirely removed from their cars but still using a stock master and booster chime in here? I will disconnect mine if necessary to answer this.
    - Does replacing the master cylinder help? I'm quite willing to swap mine if nobody else has data on this.
    - Removing vacuum from the booster results in a very firm pedal (tried this personally) but unfortunately little stopping power.

    Further questions:
    - Is there a way to insert a limiting valve at the booster vacuum line to deliver less vacuum to the booster (assuming less vacuum = less assist)?
    - If BMW simply gives us garbage master cylinders for the E36, could we perhaps create a conversion kit to a different sort of BMW master, or a different master entirely? Would an increase in master cylinder bore allow us to run a non-boosted brake system without it requiring so much effort?


    It seems like the E36 community has simply accepted the fact that the brake pedal sucks unless you get an expensive dual master setup. That's silly, we can do better.
    Last edited by Evil Spoonman; 12-14-2009 at 07:24 PM.
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  9. #84
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    Quote Originally Posted by Evil Spoonman View Post
    Speaking logically we can eliminate a few things:

    - Hard lines
    - Flexible lines
    - Calipers
    - Pedal geometry
    - Brake fluid type/bleed method
    - Pad selection


    What remains as part of the system?

    - ABS and its associated lines and hardware
    - Master cylinder
    - Booster


    So lets start eliminating the rest:
    - Does removing ABS cure the problem? Anybody with ABS entirely removed from their cars but still using a stock master and booster chime in here? I will disconnect mine if necessary to answer this.
    - Does replacing the master cylinder help? I'm quite willing to swap mine if nobody else has data on this.
    - Removing vacuum from the booster results in a very firm pedal (tried this personally) but unfortunately little stopping power.

    Further questions:
    - Is there a way to insert a limiting valve at the booster vacuum line to deliver less vacuum to the booster (assuming less vacuum = less assist)?
    - If BMW simply gives us garbage master cylinders for the E36, could we perhaps create a conversion kit to a different sort of BMW master, or a different master entirely? Would an increase in master cylinder bore allow us to run a non-boosted brake system without it requiring so much effort?


    It seems like the E36 community has simply accepted the fact that the brake pedal sucks unless you get an expensive dual master setup. That's silly, we can do better.
    Can we eliminate calipers? They can flex, as can pad backing plates under load.

    I replaced my master cylinder with new. No improvement. Others have reported the same (negative) result. However, due to class limitations I can't replace my MC with a larger-diameter one. This should be done as an experiment.

    This winter I will be replacing the booster vacuum line and check valve, as well.

    I don't know if simply disconnecting the ABS would rule that system out as a problem area, as it would still be a part of the physical plumbing from pedal to brake.

    -tammer

  10. #85
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    ^I'm sure you could insert a reducer at the brake booster valve to help make the brake pedal feel harder.

  11. #86
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    Quote Originally Posted by tammer View Post
    Can we eliminate calipers? They can flex, as can pad backing plates under load.
    True, there can be movement in the calipers. However, moving from stock sliding calipers to single piece calipers does not solve the problem. Moving to dual masters does solve the problem. Even an aftermarket pedal setup on stock calipers solves the problem. While calipers are indeed imperfect, I think that can safely be assessed as background noise vs the actual root cause.

    I replaced my master cylinder with new. No improvement. Others have reported the same (negative) result. However, due to class limitations I can't replace my MC with a larger-diameter one. This should be done as an experiment.
    I will look into this.

    I don't know if simply disconnecting the ABS would rule that system out as a problem area, as it would still be a part of the physical plumbing from pedal to brake.
    As you say, electronically disabling the ABS won't help. I was actually planning to separate the ABS entirely from the rest of the system leaving only the master, booster, and running my own discrete to-wheel lines if necessary. Perhaps there is 'give' in the ABS system someplace causing problems?
    Last edited by Evil Spoonman; 12-14-2009 at 08:09 PM.
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  12. #87
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    You can remove one caliper, or two, at a time, from the system by pinching off the flexible line with a hose clamping plier. It will not hurt the line and it will keep pressure from hitting that caliper. This way you can tell if any particular caliper is the source of the slop. I still would tend to believe the rears are the source if not because of the clip arrangements on the pads but also the self adjusting handbrake mechanism that ratchets as the pads wear.

  13. #88
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    Quote Originally Posted by Evil Spoonman View Post
    True, there can be movement in the calipers. However, moving from stock sliding calipers to single piece calipers does not solve the problem. Moving to dual masters does solve the problem. Even an aftermarket pedal setup on stock calipers solves the problem. While calipers are indeed imperfect, I think that can safely be assessed as background noise vs the actual root cause.
    I don't know if this is universally true; most people I know running stock MC w/ Stoptechs or Alcons (per Prepared class rules) don't experience the problem. It's primarily stock-MC/stock-caliper cars.

    Quote Originally Posted by Evil Spoonman View Post
    I will look into this.
    I think an E36 M3 master on a non-M E36 may work. Definitely worth checking, especially if you can pick up a used MC for cheap.

    Quote Originally Posted by ka3oxi View Post
    I still would tend to believe the rears are the source if not because of the clip arrangements on the pads but also the self adjusting handbrake mechanism that ratchets as the pads wear.
    I'm not sure I understand what you're saying here. The handbrake can be removed completely without having any effect on the hydraulic system or any parts connected to it.

    -tammer
    Last edited by tammer; 12-14-2009 at 08:54 PM. Reason: Automerged Doublepost

  14. #89
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    Quote Originally Posted by ka3oxi View Post
    I still would tend to believe the rears are the source if not because of the clip arrangements on the pads but also the self adjusting handbrake mechanism that ratchets as the pads wear.
    Um, yeah right...The handbrake mechanism has nothing to do with your brake pads. The parking brake system is a cable actuated redundant system that has nothing to do with the hydraulic brake system. The brake cable actuates brake "shoes" on the inside of the rotor hub. The hydraulic system actuates pads against the visible rotors via the calipers.
    Last edited by Michael9218; 12-14-2009 at 09:05 PM.

  15. #90
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    My apologies, but there are certain models that do not have the independent handbrake shoes and use the pads through a mechanical arrangement to actuate. It is still certainly the case in MINIs and older E-36s. Volvos consistently used shoes inside the rear discs as a drum brake until the front wheel drivers in which they adopted the ratcheting pad arrangement. Yes, I could be wrong in you case but you still can separate the rears from the system hydraulically by clamping off the flexible line and then you can test it, carefully. If the pedal get rock hard, you know where the problem lies.

  16. #91
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    ...I hate to be a debbie downer, but I doubt you could clamp the hose off. The clamps they sell for brake lines are to stop fluid when the caliper is being serviced, NOT when there is real pressure in the lines. Think about the hundreds of PSI in those lines, then think about your clamp. Besides most folks with upgraded brake systems are running steel braided lines, good luck clamping those. ...continue with discussion.
    Regards, Nate.
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  17. #92
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    I first noticed this problem last summer when I began moving new fluid through the system. It seemed in my case that changing from what looked like Guiness in my lines to nice, clear fluid upset the pedal feel.

  18. #93
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    Interesting thread.

    I too have been chasing this in my 98 M3 for years without success.

    Not sure whether this is a valid data point, but my 00 MCoupe, which I believe has substantially the same setup has never suffered from it.

    Admittedly I now have Stoptechs on the front, and previously had Brembos, but both delivered a nice high, hard pedal.

    I've just got used to the M3 pedal.

    It just catches me when I move from one car to the other, either hit the windscreen or miss the stop at the end of the driveway

  19. #94
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    Nate:

    On this one I will disagree. I have done it with both braided metal lines and rubber lines. It does not take much crush pressure to seal them off. Now if you would be concerned about deforming the lines, I would have to agree. And pinching them off with vice grips might not be advisable. But, once again, I have done it and with no ill affects with nothing more than radiator hose clamp pliers. The steel braided lines keep the hose from expansion and offers little additional strength on crush.

    I appreciate the discussion as we may give this gentleman some theory to work with and I'm always up for learning new things, but this one I have done many times over the space of 45 years as a mechanic on a variety of vehicles. Thanks for your thoughts.

    David

  20. #95
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    Quote Originally Posted by Brent 930 View Post
    ^I'm sure you could insert a reducer at the brake booster valve to help make the brake pedal feel harder.
    We looked into doing this but it is a massively expensive process (one-off parts, labor hours, fab work, etc) which is illegal for most of the spec classes.

    I have a feeling that if there was a semi-reasonably priced solution, many of the classes (Spec E36, Spec 3, etc) would allow the piece. It is just a question of a reputable shop developing such a part.

    J

  21. #96
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    It's amazing what is illegal regarding racing.

    Actually a reducer might not work because then it could hinder the braking itself.

  22. #97
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    Reducer doesn't make any sense as the pressure will equalize. On my old 95 M3 I tried (via Brenneman technique) to disconnect the booster. Not fun in a 3000lb 255whp car headed to turn 10 at Road Atlanta. I think I bent my steering wheel pulling on it. I eventually just incorporated 2-3 left foot pumps headed down any major striaght. It sure freeks out the guy behind you. Pobst had a great article in Sports Car about this 3 or 4 years ago. In a car with stock brakes, switch to the brass guides, change fluid often (jump the abs to flush it as well), and plan on replacing pads when 1/2 worn. If not, learn to drive around it.
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  23. #98
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    I'm going to go back to a previous post in this thread:


    Quote Originally Posted by BMWParkingOnly View Post
    I had the bright idea to 'rotate' my track pads on my M3 for the last event I did. I put the inners on the outside and vice versa. The result - an EXTREMELY long pedal. Swap back immediately and viola, pedal back to normal (not great, just normal). I think what we're seeing is 'cupping' of the rotor as it is hot which tapers the pad from inside to outside radius and taper of the pad from leading/trailing edge. This combines to an effective knock-back of the pad/rotor interface resulting in a longer pedal.
    I think a true floating rotor would help this scenario as well as a fixed caliper position instead of the sliders.

    That's my theory and it seems to be supported by most of the evidence supported here.
    Everyone seems to have the same story here, symptoms and solutions are consistent. What that says is design flaw.

    A restrictor will not make a difference, it won't 'firm' the pedal the way you want it to. Instead, the quick pump will be slow and less effective than before.

    I firmly believe the issue at the core is related to pad knock-back. THis is supported with my own findings (one of which is above) as well as the discussions here about fresh pads helping the issue. The stock type rotors change shape as they are heated in a brake event (they 'cup' or 'tulip'). That coupled with any axial play/run-out knocks the pad away from the rotor and thus, the piston back into the bore. So the next brake event requires you to close the gap first before the pad bites the rotor. The rotor has changed shape again (not cupped) because it has cooled and the pad face isn't parallel to the rotor.
    Now, allow the caliper to rotate relative to the rotor (flex in the sliders) and have additional pad taper and you have a combination of movement that results in a lot of pedal travel to get to the firm pedal point.

    The booster only amplifies the force you apply at the pedal. If you can get a firm pedal with the engine off, you don't have a leaking MC seal. The flex you feel is compliance in the pedal, firewall, lines and flex at the caliper itself.

    I haven't tried this yet - anyone here have the Euro semi-floating rotors and experienced the issue?

    I use the same rotor on the street and the track and only swap pads. It takes several sessions before I get even wear indications on the front rotors (inside and outside of the rotor from center to edge). Then when I swap back, my street pads take a long time to contact the entire rotor surface as well. All that contributes to knock-back and thus, pedal travel.

  24. #99
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    David - my appologies, I was wrong.

    Knockback - This is hardly a design flaw, considering that most systems struggle to get the piston to retreat. If you believe that rotor-pad gap is the culprit, shim your pad closer. Guys on the street might have to deal with excess chatter or rattle.
    Last edited by TOOLEAN; 12-15-2009 at 03:22 PM.
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    Quote Originally Posted by tammer View Post
    I don't know if this is universally true; most people I know running stock MC w/ Stoptechs or Alcons (per Prepared class rules) don't experience the problem. It's primarily stock-MC/stock-caliper cars.
    Fair enough. This is why I figured switching to a single-piece caliper would help, because it seems people have had success when they do so. That being said, I still have the problem with Wilwood Superlites all around. It could be that Wilwoods suck, but they seem reasonably similar to said Stoptechs. Anybody else have this braking setup?

    Quote Originally Posted by thefoxguy82 View Post
    I first noticed this problem last summer when I began moving new fluid through the system. It seemed in my case that changing from what looked like Guiness in my lines to nice, clear fluid upset the pedal feel.
    We should try Guiness, maybe it is an excellent hydraulic fluid. (I just want an excuse to buy some, shhhh.)

    Quote Originally Posted by BMWParkingOnly View Post
    Everyone seems to have the same story here, symptoms and solutions are consistent. What that says is design flaw.

    A restrictor will not make a difference, it won't 'firm' the pedal the way you want it to. Instead, the quick pump will be slow and less effective than before.

    I firmly believe the issue at the core is related to pad knock-back. THis is supported with my own findings (one of which is above) as well as the discussions here about fresh pads helping the issue. The stock type rotors change shape as they are heated in a brake event (they 'cup' or 'tulip'). That coupled with any axial play/run-out knocks the pad away from the rotor and thus, the piston back into the bore. So the next brake event requires you to close the gap first before the pad bites the rotor. The rotor has changed shape again (not cupped) because it has cooled and the pad face isn't parallel to the rotor.
    Now, allow the caliper to rotate relative to the rotor (flex in the sliders) and have additional pad taper and you have a combination of movement that results in a lot of pedal travel to get to the firm pedal point.

    The booster only amplifies the force you apply at the pedal. If you can get a firm pedal with the engine off, you don't have a leaking MC seal. The flex you feel is compliance in the pedal, firewall, lines and flex at the caliper itself.

    I haven't tried this yet - anyone here have the Euro semi-floating rotors and experienced the issue?

    I use the same rotor on the street and the track and only swap pads. It takes several sessions before I get even wear indications on the front rotors (inside and outside of the rotor from center to edge). Then when I swap back, my street pads take a long time to contact the entire rotor surface as well. All that contributes to knock-back and thus, pedal travel.
    This is interesting, thanks for the thorough thought process. I can see what you're saying, and how it would act to create the condition I experience. I would like to know if you have any thoughts as to how it would continue to affect me with a single piece caliper setup?
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