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Thread: Brake Pedal Feel Issue

  1. #51
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    does the pedal firm up if you do a second push? if so, it could be pad taper, caused by caliper twisting. if it is always soft, taper is not likely the problem. brakes can be so frustrating-trying to chase too many variables.

  2. #52
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    Quote Originally Posted by smeyer1116 View Post
    does the pedal firm up if you do a second push? if so, it could be pad taper, caused by caliper twisting. if it is always soft, taper is not likely the problem. brakes can be so frustrating-trying to chase too many variables.
    No, not really. I give a tap with the left foot heading into a big braking zone (for T7 at the end of the back straight at Mid-Ohio, for instance, but it doesn't improve matters. Here is a picture of a set of Hawk HT-10s I removed during the weekend. You can see two things here: the (minimal) taper I get, and a nasty tendency Hawk pads have to disintegrate quickly when they get thin. Notice how one outboard pad (on the right in the photo) is almost gone? Before the session, all of the pads looked identical. I was warned of this when I started using the HT pads, but this is the first time it's happened to me. Glad I took the advice to check every session once they're past half-worn.



    -tammer

  3. #53
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by tammer View Post
    ..Notice how one outboard pad (on the right in the photo) is almost gone? Before the session, all of the pads looked identical. I was warned of this when I started using the HT pads, but this is the first time it's happened to me. Glad I took the advice to check every session once they're past half-worn.
    When I was running stock brakes (I now have StopTechs that I got from Jack a couple of years back) I also used Hawks. The first thing I'd do on taking them out of the box was to take a grinder to the head of the rivet that holds the clip to the inboard pad. The clip then drops right off.

    This allows swapping pads inboard to outboard, with the taper leading or trailing, to equalize wear. It's a no-cost, no-brainer measure to improve pad life. I don't understand why Hawk even bothers to install those clips on race pads. PF doesn't, as I recall.

    Slight thread hijack: several years ago I bought a set of the brass guide pin bushings that Shea mentioned, but I never installed them and obviously never will now. I've got the full set of 8 for both axles, including guide pins and circlips, all shiny and new. If anyone wants to make a semi-reasonable offer for them, they could be yours (BW sells them for $55 per axle.)

    Neil

  4. #54
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    PM sent, Neil.

    -tammer

  5. #55
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by tammer View Post
    The piston retracts enough that the wheel will spin freely when jacked up, but I thought that is normal, healthy behavior (no pad dragging/caliper binding)
    Yeah that's normal, but they shouldn't retract too much. If you wear off, say, 0.5mm from each brake pad, then the single piston has to adjust by 1mm to maintain clearance. It does that by an odd process of "walking" on the square edges of the caliper seal. If the piston is either too tight or too loose in the caliper bore it won't do that right, and even a small amount of extra pad to rotor face clearance translates to appreciable pedal travel. Have you rebuilt your calipers lately? I used to burnish the pistons and the caliper bore with Scotch-Brite to make sure everything moved smoothly.

    I don't know that this is the most likely thing, but then again you've already chased the obvious. As Scott said, "brakes can be so frustrating - trying to chase too many variables."

    Neil

  6. #56
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    Quote Originally Posted by NeilM View Post
    Yeah that's normal, but they shouldn't retract too much. If you wear off, say, 0.5mm from each brake pad, then the single piston has to adjust by 1mm to maintain clearance. It does that by an odd process of "walking" on the square edges of the caliper seal. If the piston is either too tight or too loose in the caliper bore it won't do that right, and even a small amount of extra pad to rotor face clearance translates to appreciable pedal travel. Have you rebuilt your calipers lately? I used to burnish the pistons and the caliper bore with Scotch-Brite to make sure everything moved smoothly.

    I don't know that this is the most likely thing, but then again you've already chased the obvious. As Scott said, "brakes can be so frustrating - trying to chase too many variables."

    Neil
    The calipers were rebuilt 3 events ago. I have a spare set of rebuilt front calipers that I keep around in case one hangs up at the track; I can try putting them in. I want to do this sequentially, though, so I can figure out what the culprit is. I think the order will be:

    1) Motul fluid
    2) Brass guide pins (caliper flex)
    3) Replace booster vacuum line and check valve
    4) Different pad manufacturer
    5) Switch calipers to fresh(er) rebuilds
    ------ (that's the list of cheap/easy fixes)
    6) New booster
    7) Disable ABS pump

    -tammer

  7. #57
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    Tammer, those bushings aren't spec legal (or I would have bought them!).

    See you at NJ?
    Brian
    SE36 #206

  8. #58
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    Quote Originally Posted by bbh03 View Post
    Tammer, those bushings aren't spec legal (or I would have bought them!).

    See you at NJ?
    I know, but I can be the guinea pig this year and figure out where the problem lies in the stock system. If the bushings are the only thing that improve it, it might be worth asking for a rules change. If not, I've risked a relatively small amount of money. I'm really curious about this now, though.

    -tammer

  9. #59
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    Got it - go for it.
    Brian
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  10. #60
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    Tammer:
    i was at mid ohio and had similar problems with a soft pedal after there was pad wear. i have had it before, and it goes away when i put new pads on. i have a really smart friend who explains it this way:
    1. pads taper because the outer edge is meeting a rotor which is traveling faster than the inner edge meeting point. same with leading/trailing edges.
    2. this causes pad taper out to in, and leading edge to trailing edge
    3. with pad taper of only 40 thousanths, you will get a long, soft stroke, because the piston is pushing the "thick" part of the pad first, then the pad cocks to get full contact.
    rebuilding calipers can make this worse, because the new seal will pull the pad back slightly further than the worn seal did-therefore, you have to make up more distance when you first apply pressure.
    suggestion: measure the pad thickness, see if there is taper-might be the answer
    scott

  11. #61
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    Quote Originally Posted by smeyer1116 View Post
    Tammer:
    i was at mid ohio and had similar problems with a soft pedal after there was pad wear. i have had it before, and it goes away when i put new pads on. i have a really smart friend who explains it this way:
    1. pads taper because the outer edge is meeting a rotor which is traveling faster than the inner edge meeting point. same with leading/trailing edges.
    2. this causes pad taper out to in, and leading edge to trailing edge
    3. with pad taper of only 40 thousanths, you will get a long, soft stroke, because the piston is pushing the "thick" part of the pad first, then the pad cocks to get full contact.
    rebuilding calipers can make this worse, because the new seal will pull the pad back slightly further than the worn seal did-therefore, you have to make up more distance when you first apply pressure.
    suggestion: measure the pad thickness, see if there is taper-might be the answer
    scott
    That makes sense and could be the issue. I do get visible taper front-to-rear along the pads; if there is taper top-to-bottom (from outer rotor edge to inner rotor edge), it's too small to see with the eye. I'll pull the new pads off and measure them this weekend. If this is the culprit, what does one do to correct it besides brass guide pins (not SE36 legal, as Brian pointed out) or shimming with extra backing plates (only marginally effective, you have to wait until the pad is worn enough to fit another backing plate in the caliper)?

    -tammer

  12. #62
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    Tammer,
    Is the pedal firm when you are sitting still and apply the brakes? Are you only having issues when driving? That would at least narrow down the possible cause to the caliper and pads.

    My pedal feels the same (mushy) regardless of moving or not. So it isn't pad compound, pad taper, or even guide pins.

    P.S. I have Motul 600 in the car now, and have had similar results with AP Racing Fluid and ATE.
    Last edited by matt325; 05-27-2009 at 06:14 PM.

    Matt
    1994 325is Spec3

  13. #63
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    Tammer,
    Is the pedal firm when you are sitting still and apply the brakes? Are you only having issues when driving? That would at least narrow down the possible cause to the caliper and pads.

    My pedal feels the same (mushy) regardless of moving or not. So it isn't pad compound, pad taper, or even guide pins.

    P.S. I have Motul 600 in the car now, and have had similar results with AP600 and ATE.

    Matt
    1994 325is Spec3

  14. #64
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    Quote Originally Posted by matt325 View Post
    Tammer,
    Is the pedal firm when you are sitting still and apply the brakes? Are you only having issues when driving? That would at least narrow down the possible cause to the caliper and pads.

    My pedal feels the same (mushy) regardless of moving or not. So it isn't pad compound, pad taper, or even guide pins.

    P.S. I have Motul 600 in the car now, and have had similar results with AP600 and ATE.
    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

  15. #65
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    Tammer:
    i have an E30M3 with the brass bushings (legal in Mod) it does not cure the problem, just postpones it as a result of less caliper twist. i wish i had a solution, but it seems that as long as you have calipers that can deform, you will have this problem to some extent. my very smart friend is working on it, if he comes up with something practical i will post it. right now, the brakes work, just feel mushy.

  16. #66
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    I can confirm that brass bushings dont fix the problem (at least not for me). Basically the only thing I havent done (short of getting a BBK) is changing the front wheel bearings. I have quite literally the exact same symptoms as Tammer. When I switched in brand new PFC06 pads the brake feel did improve marginally but as soon as my worn (~50%) PFC-Z street pads were back in the pedal was the same as always.
    Last edited by VengeanceM3; 05-28-2009 at 01:31 AM.

  17. #67
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    I figured I'd chime is even though I haven't made much of an effort to fix the problem. I picked up this mushy pedal feel half way through my driving school at Watkins Glen. I really have to push the pedal deep and hard to brake. It makes it very difficult/awkward to heel toe since the pedal goes down to so far. I'll be trying a few things imentioned in this thread in the coming weeks to see if I can resolve it.

  18. #68
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    I put used HPS pads on 4 brand new rotors. I got a long pedal instantly. Unfortunately I replaced the rear callipers at the same time so I have tow variables to consider...

    After reading this tread I took a look at the rotors and one can clearly see a different pad transfer rate (colour) from the outside to the inner hub. Sounds like pad taper mismatch with the new rotors.

    I guess the recommendation to match pads to rotors is not just a way to sell more parts !

    I'm keeping the brass bushings. And buying more rotors. Interesting that it's the cheapest part of the entire system.

  19. #69
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    Quote Originally Posted by Franky goes View Post
    I put used HPS pads on 4 brand new rotors. I got a long pedal instantly. Unfortunately I replaced the rear callipers at the same time so I have tow variables to consider...

    After reading this tread I took a look at the rotors and one can clearly see a different pad transfer rate (colour) from the outside to the inner hub. Sounds like pad taper mismatch with the new rotors.

    I guess the recommendation to match pads to rotors is not just a way to sell more parts !

    I'm keeping the brass bushings. And buying more rotors. Interesting that it's the cheapest part of the entire system.
    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.

  20. #70
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    ^^^

    But how come some cars even race cars with 100's of thousands of miles do not have these symptoms? I am having this issue as well. Before I thought it was fixed but now I switched to pfc z rated front pads and the pedal felt awful. The pads stop great and the brakes work well but the pedal was terrible. I bled it using the old fashion (2 person style) and it helped it slightly, even bled it at the master, which seemed to help the most, but it's still mushy and long. In case you guys didnt know about a year ago I went through this problem and went about trying to find a solution. I replaced the master cylinder, which did nothing, followed by the booster, which seemed to correct it but I was never truly satisfied with my pedal feel. Just yesterday when I swapped in the pfc z rated from HPS' my pedal went back to that awful feeling again. Before it was manageable but now it feels about as bad as it ever has.

    It's interesting people have talked about left foot braking feeling (right foot on the throttle) but under normal braking (off the throttle) the pedal is mush. I tried left foot braking on the street today as I was fooling around and it seemed to feel firm while on the gas. It could be in my head since my left foot is not used to really touching the brakes so it's hard to say if the pedal was really higher and firmer.

    I honestly have no idea what to do at this point. I'm basically just going to deal with it until somebody can find a true solution. Let's keep this thread updated as much as possible with any new ideas.

    -Nick
    Last edited by savage217; 06-26-2009 at 12:19 AM.

  21. #71
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    Quote Originally Posted by savage217 View Post
    It's interesting people have talked about left foot braking feeling (right foot on the throttle) but under normal braking (off the throttle) the pedal is mush. I tried left foot braking on the street today as I was fooling around and it seemed to feel firm while on the gas. It could be in my head since my left foot is not used to really touching the brakes so it's hard to say if the pedal was really higher and firmer.
    When you're on the throttle there is no longer a vacuum in the intake to replenish the booster so you lose the assist.
    S50'ed 318is

  22. #72
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    Quote Originally Posted by brew View Post
    When you're on the throttle there is no longer a vacuum in the intake to replenish the booster so you lose the assist.
    I tried disconnecting the brake booster and the pedal feel was awesome. Too bad I can't say the same for braking, it took my whole weight on the brake pedal to get it to actually stop. I dont understand how some people could track the car that way. Honestly I was pushing as hard as I could with my leg to stop the car and it didnt even stop anywhere near the power they normally do with the booster.

  23. #73
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    This is what you need for pedal feel Nirvana!

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  24. #74
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    Quote Originally Posted by savage217 View Post
    I switched to pfc z rated front pads and the pedal felt awful.
    So all you did was push back the pistons and put new pads on the old rotors? Might you just be feeling the new flat pads having to wear themselves into the wear profile of your old rotors?

    I swap/rotate pads all the time to even out wear. It does take a bit for the pad to wear in (first few laps). There is some wisdom to replacing or turning rotors when they start to get "unflat".

    If I put old pads on new rotors, I do bed them in, partly to wear the pad flat again. You can look at the rotors and tell when the pads are flat because they've deposited material everywhere, with no bare (material-less) rings.
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  25. #75
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    Quote Originally Posted by Evergreen Dan View Post
    So all you did was push back the pistons and put new pads on the old rotors? Might you just be feeling the new flat pads having to wear themselves into the wear profile of your old rotors?

    I swap/rotate pads all the time to even out wear. It does take a bit for the pad to wear in (first few laps). There is some wisdom to replacing or turning rotors when they start to get "unflat".

    If I put old pads on new rotors, I do bed them in, partly to wear the pad flat again. You can look at the rotors and tell when the pads are flat because they've deposited material everywhere, with no bare (material-less) rings.
    I guess it's possible since before the pedal was higher. I did kind of break them in though; did a few 70-30 stops and have driven on them a bit now. Hopefully it does get higher.

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