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Thread: Brake Pedal Feel Issue

  1. #101
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    Quote Originally Posted by TOOLEAN View Post

    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.
    It has nothing to do with a shim or a fixed 'gap', the pad (and ultimately piston) gets knocked back into the bore by a change in geometry of the rotor with thermal cycling and/or brake torque application and release. This isn't something that is designed into a system to reduce brake drag. The piston seals, etc. do that.

    You eliminate it by changes in the system (floating rotors, fixed position calipers, etc). Or you mask it by a change in the ratio of MC to piston bore size, but if you do that - it changes other performance aspects of the system.

    Quote Originally Posted by Evil Spoonman View Post
    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?
    If the rotors are standard OE cast iron units (not full floating or semi-floating designs) it could be the root in your case. Otherwise the ratio of MC bore to piston bore (effectively generating brake torque from pedal force) as well as pad surface area. In your case (UUC kit, right?) what MC are you using now?
    Last edited by BMWParkingOnly; 12-15-2009 at 03:21 PM. Reason: Automerged Doublepost

  2. #102
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    Quote Originally Posted by BMWParkingOnly View Post
    If the rotors are standard OE cast iron units (not full floating or semi-floating designs) it could be the root in your case. Otherwise the ratio of MC bore to piston bore (effectively generating brake torque from pedal force) as well as pad surface area. In your case (UUC kit, right?) what MC are you using now?
    This is a UUC four wheel kit. Wilwood Superlite front and rear, braided steel lines, UUC's E46 M3 rotors, ATE Superblue fluid, and I get this problem with both street and track pads (DTC-05 and Carbotech XP12 respectively). Using a stock E36 328i Master Cylinder. From what UUC tells me, this kit is designed specifically for this car as far as caliper piston size is concerned. Moving to this setup DID improve pedal feel, but the firmness and excellent modulation that comes with doesn't show up until a good ways through the travel. Fluid was flushed by me (bleed, go engage ABS, bleed, repeat method), and by the dealer (special tool to cycle ABS). No improvement.
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  3. #103
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    It's only "knockback" if the long pedal is noticed after a series of left-right transitions.

    Much more common is "piston cocking", due to pad taper. Look closely at this extreme case of pad taper:



    See the gap between the pad and the lower part of both pistons? That gap reopens each time you release the brakes, and needs to be reclosed each time you reapply the brakes, causing a long pedal.

    Fixing this is hard Obviously, minimizing taper will help. Knockback springs might help to keep the piston rotated to match the pad, dunno.

  4. #104
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    ^ Are the smaller pistons on the leading edge of the caliper?

  5. #105
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    Quote Originally Posted by Greg S View Post
    ^ Are the smaller pistons on the leading edge of the caliper?
    All four pistons are the same diameter (1.75"). Heaven knows why - it causes the pads to wear more at the leading piston. I'm hoping that flipping them every day will even things up.

  6. #106
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    Quote Originally Posted by flink View Post
    All four pistons are the same diameter (1.75"). Heaven knows why - it causes the pads to wear more at the leading piston. I'm hoping that flipping them every day will even things up.
    I questioned this design as well when I got them. Seems smaller leading edge pistons would be standard on all multi-piston calipers. My DTC-05s got a slight visible taper after a few thousand (hard, I've been abusing them) street miles, I swapped them and it seems to have evened out fine.
    Last edited by Evil Spoonman; 12-15-2009 at 07:10 PM.
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  7. #107
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    Quote Originally Posted by Evil Spoonman View Post
    I questioned this design as well when I got them. Seems smaller leading edge pistons would be standard on all multi-piston calipers. My DTC-05s got a slight visible taper after a few thousand street miles, I swapped them and it seems to have evened out fine.
    Yup. I don't know how that pad got so tapered (it came that way from the previous owner). The passenger side pads hadn't done that.

    Maybe the cocking angle got so high that the trailing piston bound up in the bore and stopped applying full pressure. I noticed scoring marks on all eight pistons when I was replacing the seals.

    I'm not very impressed by the superlites. They seem flimsy, they bend rather a lot under pedal pressure and they have this poorly-chosen piston size problem. I'll wait and see how they get on as the pads wear down before making any replacement decision.

  8. #108
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by Evil Spoonman View Post
    Using a stock E36 328i Master Cylinder.
    So you'd have the option of switching to the larger diameter E36 M3 M/C, which ought to firm things up and reduce pedal travel, while increasing pedal effort somewhat. Not an inexpensive swap at $500 or so.

    I get some pad taper even with my staggered piston size StopTechs. Nothing like as bad as the photo above though. To equalize wear I do flip the pads periodically, which is reasonably quick to do with these and most fixed caliper designs. The StopTechs did give a noticeably better pedal feel when I fitted them, although I still wouldn't say it's the firmest brake feel ever.

    I'm inclined to agree that there is something in the E36 brake system design that doesn't allow the firmest pedal.

    Neil

  9. #109
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    Quote Originally Posted by flink View Post
    It's only "knockback" if the long pedal is noticed after a series of left-right transitions.

    Much more common is "piston cocking", due to pad taper. Look closely at this extreme case of pad taper:



    See the gap between the pad and the lower part of both pistons? That gap reopens each time you release the brakes, and needs to be reclosed each time you reapply the brakes, causing a long pedal.

    Fixing this is hard Obviously, minimizing taper will help. Knockback springs might help to keep the piston rotated to match the pad, dunno.
    Is it me, or is the rotor also not centered and true to the caliper?
    Perhaps, it is flexing but doesn't look right.

  10. #110
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by ncoker View Post
    Is it me, or is the rotor also not centered and true to the caliper?
    Perhaps, it is flexing but doesn't look right.
    That's because one of the pads shown is more worn and tapered than the other. The floating rotor self-centres to accommodate that.

    Neil

  11. #111
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    Quote Originally Posted by NeilM View Post
    The floating rotor self-centres to accommodate that.
    Floating rotors allow that much axial movement? Wow. I thought it was a fraction of a mm, just enough to thermally decouple the hat.
    Dan Chadwick
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  12. #112
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    Angle of the camera make it look not centered.

    Might also be because (don't know...) that the rotor bolt that holds it to the face of the hub isn't installed. The rotor will flop around without the wheel on.

    The caliper is a FSL - it's not the biggest and so isn't the stiffest caliper. It's a good caliper for the money, but not as good as more expensive calipers.
    Last edited by osborni; 12-17-2009 at 12:50 PM.
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  13. #113
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by Evergreen Dan View Post
    Floating rotors allow that much axial movement? Wow. I thought it was a fraction of a mm, just enough to thermally decouple the hat.
    Depends on the particular design. BMW floating rotors (E36 M3 Euro and E46 M3 CSL) don't allow any axial movement of the friction disk, only radial. But then they're (normally) used with sliding calipers. I haven't measured my StopTechs, but I'd guess their axial freedom of movement at fractions of a millimetre, as you suggest. I've seen motorcycle and other rotors that allow much more though.

    But I think osborni is likely right — we don't really know the circumstances under which the photo was taken, so it's a bit hard to know what we're seeing.

    Neil

  14. #114
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    Nice suggestions are there for brake pedals. I am going to utilize it very soon.

    BMW Parts Wheels
    Last edited by Simi Smith; 12-18-2009 at 03:54 PM.

  15. #115
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    While browsing around on wilwoods website, I noticed a residual pressure valve part number 260-1874. Their website said

    "Residual Pressure Valve 10lb, Red, w/o Fittings.

    Wilwood two pound residual pressure valves retain a minimum brake line pressure to help eliminate excessive pedal travel in both disc and drum brake systems"


    I wonder if this might help some of the op's squishy-ness

    Here is the link
    http://wilwood.com/MasterCylinderValves.aspx
    Last edited by BMWjiggaB; 01-03-2010 at 11:14 PM.

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  16. #116
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    ^ Yes Residual Pressure Valves would help (in theory) but I hesitate because this is more of a "band aid" fixe. These were orginally designed for cars that were converted from drum to disc brakes in the rear. These also create a nasty "knee" in the pressure plot measured within the brake line (post vavle). On the other hand, it would be a cheap, quick, test.
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  17. #117
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    Has anyone come up with a fix for the pedal travel on the e36? I have a 1995 m3 and it just feels like slop when driving around town. Sure when you're on the track you stomp on it and don't notice it much, but just pressing on the pedal does not brake compared to other cars.

    In comparison we have an 04 Jetta Wagon 8V that has strong braking power on just a little press of the pedal. What can be different from these two cars? How is the e46 m3? Does it have the same problem? I feel like I need to swap a booster in or something. The e36 just feels so sloppy.

    (BTW Just installed New Rotors, Hawk HPS all around, SS lines, Bled w/ power bleeder then two man method until I was blue in the face just this past weekend. I then noticed after this that the pedal feel did not feel like that of ordinary other passenger vehicles that I drive on a regular basis.)

  18. #118
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    Quote Originally Posted by Pink View Post
    ... two man method until I was blue in the face
    Stop sucking the brake fluid out by mouth?

    Have you considered pad knockback? Try tapping the brakes lightly once before braking, then brake. The first tap may bring the pads back in contact with the rotors. If this solves the problem with fresh rotors and pads, I'd suspect a wheel bearing, maybe.

    If you have this with used pads / rotors (e.g. when swapping in pads at the track), then some of it will be that the two have to wear to mate to each other (something that takes a few laps).

    Or it could be just the way it is -- some pedal travel before you start getting friction.
    Dan Chadwick
    Boston Chapter BMW CCA Instructor Development.
    Near-Orbital Space Monkeys, E30 M50-ish
    Driving Evals on-line evaluations for Driving Schools. Paper forms are just wrong.

  19. #119
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    As much as I like Mcclaskz I will say that trying out the non boosted setup at Road A probably was not the place to try and get used to it. LOL But I have been running non boosted for 3 years now and I love the way the brake pedal feels. It is high and firm and I have no trouble generating enough brake force. I can get into the abs anytime I want to. Now I will say I am 6'2 and athletic so I may be more physically able to deal with the unboosted setup than some.

    Now I do have some anecdotal evidence that may throw some extra light on the subject. In the stripped out car when I hit the brakes sitting still with the motor off I get a lot of fluid flow noise through the lines up under the rear of the car. It seems to be coming from the splitter fitting up around the fuel tank. It just seems like no matter how new the pads are there is a lot of fluid flow noise to the rear of the car when the brakes are applied. Just my own observation.
    Ryan
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  20. #120
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    It seams there is some confusion between knockback and some other issue. YMMV, bad boosters can cause problems that seam like knockback. Knockback has already been described, my personal experience is with bad wheel bearings causing it. Air in the lines or ABS system can also feel the same. The only real option is the slowly work through all the potential problem areas with new parts.
    - Ian
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    46mm wheel bearing socket for rent - $30 deposit + $10 fee. PM for details.

  21. #121
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    Simple improvement

    Hello, I am new to the forum. I just remembered watching a Youtube of Jackie Stewart test driving Benton F1 from the nineties and telling the mechanic to add a “wooden wedge” somewhere on the brake pedal for, I am guessing, a better feel. We all agree that the performance of the brakes is acceptable for these particular cars when properly maintained. The issue is the break pedal travel primarily when trying to h&t, at least to me it is. I would like the brake pedal to feel like hitting a brick wall but that is not going to happened with this hydraulic system. After reading everybody's comments and thinking about what my preference would be I decided to simply add “thickness” to the pedal. Just for testing purposes I duck-taped square peace of ½ in thick wood on top of the brake pedal. When I drove it the brakes felt just right to me. I did not feel weired or as if I had to beck of my foot to engage the brake. There was a good stopping force before the pedal got too deep and at that point it already felt firm. I am planning on making this “pedal pad” out of Aluminum and fitting it to the pedal with nice bolts and shims for adjustment. I have to say I have not had chance to test it on the track, but I can not see the drawbacks. I am also planning to replace/improve all the bushings for the pedal just to take that play out of equation as much as possible. We all know that the top racing teams deal with these kinds of adjustments all the time just to make the driver happy.

  22. #122
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    Bump....

    Has there been any solution found to the terrible e36 brake pedal?

    I don't have to abide by any class rules; just a daily driven canyon car, so ANY cost effective solution would be awesome.

  23. #123
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    Left foot tap before every brake zone. New pads pads when 1/2 used. You get used to it. Brakes work fine.
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  24. #124
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    Quote Originally Posted by Pink View Post
    Has anyone come up with a fix for the pedal travel on the e36? I have a 1995 m3 and it just feels like slop when driving around town. Sure when you're on the track you stomp on it and don't notice it much, but just pressing on the pedal does not brake compared to other cars.

    In comparison we have an 04 Jetta Wagon 8V that has strong braking power on just a little press of the pedal. What can be different from these two cars? How is the e46 m3? Does it have the same problem? I feel like I need to swap a booster in or something. The e36 just feels so sloppy.
    I have both E36 318is and E46 M3 and the pedal feel and brake effectiveness on both are like night and day. E36 pedal goes to floor and feels generally mushy while E46 M3 needs only little pedal pressure until you are activating ABS.

    I have devised a plan for E36:

    1. E36 M3 master cylinder with +13.5% more piston area and hence same amount less pedal travel (already have the part, just need to install it)

    2. Teflon/steel brake hoses (already on the way)

    3. change brake pedal leverage by drilling new hole for brake cylinder piston bit lower on pedal arm. This should shorten the pedal travel and increase the required pedal pressure. I think perhaps 5-10mm or so should yield noticeable difference.

    The last one is so obvious I wonder why no-one has tried it and reported how it works? Perhaps there is something I have missed but to me it seems pretty straightforward and effective mod

    I think I will also devise DIY BBK from Wilwood parts. Big rotors to maximize effective pad lever arm, high Cf pads and moderately sized brake caliper pistons (allowed by big rotor and high Cf pads) to keep pedal travel in check.

  25. #125
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    Mushy pedal

    I have also been chasing this long pedal for some time.

    1998 328i
    Stock calipers, fully rebuilt, brass guides
    Stainless lines
    ATE Blue fluid
    Carbotech pads
    Cross drilled rotors
    Beld, bled, bled - pedal, pressure, ABS valves cycled, etc.
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    I am currently playing with an adjustable valve installed on the vacuum line to the booster. This is a false hope I think.

    I have assessed all the pad knock back info, BUT this happens when the car is sitting and not moving - car off: pedal is good, car on, pedal travel sucks.

    Let me know how the re-drilled pedal feels. I cannot wait to get a firm pedal.

    Cheers.

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