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Thread: ABS intermittent

  1. #26
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    Quote Originally Posted by aeronaut View Post

    Do explain.
    In one case, ABS went into "ice mode", limiting maximum braking force by 30-40% coming into T10 doing over 140 at Road Atlanta. I didn't leave that much on the table. The other was a cold track/cold tire/old tire situation, for which I take the blame. Not enough traction to get the wheels turning again after lockup and ABS activation, especially once I hit frosty grass. Without ABS I might have still have gone off, but I could have slowed the car in the grass enough with the wheels locked to have avoided contact.

    I tried pulling the ABS fuse once, and had the car snap 90 degrees at 130+. Haven't tried it again. It surprised the crap out of me, as I rarely get into ABS operation on track. Guess I'm not braking hard enough...
    '95 M3 S54 Track Toy
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  2. #27
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    Ug, ice mode. That crap scares me.

  3. #28
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    Update:
    Resistance of sensors checked, all ok. (1.02-1.12K ohms).
    Resistance of brake pedal travel sensor checked, ok. (250-550 ohms, while still installed in car).

    I'll check voltage output of the 4 sensors when I get a 3rd hand.

    FYI, the bavauto blog referenced above, and the Bentley manual, are wrong and/or confusing on the pin outs at the ABS computer to measure the ABS sensors.
    For a 1995 E36 M3, non traction control, here's what I figure out as the correct pin orientation, and location of the 4 abs sensors at the ABS computer connector:



    Oh, For the record, I'm talking about this controller/computer and this connector (ABS controller under the glove box, to the right).




    Last edited by aeronaut; 05-02-2017 at 04:31 PM.

  4. #29
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    Quote Originally Posted by aeronaut View Post
    Update:
    Resistance of sensors checked, all ok. (1.02-1.12K ohms).
    Resistance of brake pedal travel sensor checked, ok. (250-550 ohms, while still installed in car).

    I'll check voltage output of the 4 sensors when I get a 3rd hand.

    FYI, the bavauto blog referenced above, and the Bentley manual, are wrong and/or confusing on the pin outs at the ABS computer to measure the ABS sensors.
    For a 1995 E36 M3, non traction control, here's what I figure out as the correct pin orientation, and location of the 4 abs sensors at the ABS computer connector:

    Oh, For the record, I'm talking about this controller/computer and this connector (ABS controller under the glove box, to the right).
    Thanks for this! Going to try tonight. What pins did you check for the pedal sensor?

  5. #30
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    Quote Originally Posted by olemiss540 View Post
    Thanks for this! Going to try tonight. What pins did you check for the pedal sensor?
    I just unplugged the sensor at the brake booster. And clipped the meter to the sensor. Easy access.

  6. #31
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    HPDE this weekend was 'fun'. FAR too much rear bias. Rears lock up at what feels like when fronts are at 50%. That can't be the best setup even with ABS on.
    Anyway, some moments of 'blue smoke' and a few good slides into slow speed corners...trail braking was touchy with that much rear and so little front.
    And seriously, it was FUN if not fast.

    Measured voltages at senders today. No joy; all 4 looked ok at the slow speeds I could turn the tires by hand.

    I guess off to a dealer this week and pay my dues to get codes (hopefully) read.

  7. #32
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    Quote Originally Posted by aeronaut View Post
    HPDE this weekend was 'fun'. FAR too much rear bias. Rears lock up at what feels like when fronts are at 50%. That can't be the best setup even with ABS on.
    Anyway, some moments of 'blue smoke' and a few good slides into slow speed corners...trail braking was touchy with that much rear and so little front.
    And seriously, it was FUN if not fast.

    Measured voltages at senders today. No joy; all 4 looked ok at the slow speeds I could turn the tires by hand.

    I guess off to a dealer this week and pay my dues to get codes (hopefully) read.
    This is spooky, very much the same as my recent battle. I went with a staggered pads compound to correct my rear bias issue, but not before making the rear tires more of an octagon than a circle.... Let us know what the dealer finds.

  8. #33
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    Dealer says NO CODES found. 150 bucks, and didn't even get a car wash. lol.

  9. #34
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    Quote Originally Posted by olemiss540 View Post
    This is spooky, very much the same as my recent battle. I went with a staggered pads compound to correct my rear bias issue, but not before making the rear tires more of an octagon than a circle.... Let us know what the dealer finds.
    What pad setup do you have?

  10. #35
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    I have run PFC 01 all around, PFC 08 all around, PFC 01F PFC 08R and am now on Hawk DTC 70F/DTC 60R.

    Front bias seems corrected with the PFC 01F/08R and DTC 70F/60R and would love to keep running the PFC's but was trying to save on the budget. Will probably go back since the Hawks have had pad deposit issues on first weekend (new centric rotors all around) and not as much stopping power as the 01's IMO....

  11. #36
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    Hmmm...maybe I'll get me a set of PFC11's for the front before next weekend.

  12. #37
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    Final UPDATE (unless)...
    I replaced 3 of 4 ABS sensors (received 1 of 4 bad replacement from Rock Auto, so couldn't use it), and intermittent ABS problem reoccurred during 2nd track session of the day. Removed that 4th sensor (front) to replace with the other used sensor I had, and a friend noticed a crack in it (even though it tested properly).

    So, replaced the cracked one with the old one, then ran 1.5 days without any ABS failures. YAAAAA!!

    Moral of the story...
    - sensors measured OK in both resistance and voltage, but replacing sensors has fixed the problem (at least for now, will update if it shows up again).
    - Rock Auto has disappointed me. 1 bad sensor received (dry rotted), and the replacement for that was an incorrect sensor (opened box containing wrong sensor). And now they're out of stock. I wouldn't be posting a bad review on Rock Auto if the replacement they sent had been NEW, but it was obviously a return item in an open box, with the internal packaging (plastic bag) cut open, containing the wrong part #.

  13. #38
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    Well, CRAP. Problem isn't fixed. Back to trying to figure out what's going on. Same symptoms as original post, which started 2nd lap of first session.

    https://vid.me/b2Gi

  14. #39
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    Check the pedal travel sensor yet? Those were the EXACT same symptoms I had, which continued after replacing all 4 ABS sensors. Turned out to be the pedal travel sensor.
    97 M3 - SCCA TT Prepped
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  15. #40
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    Quote Originally Posted by matthugie View Post
    Check the pedal travel sensor yet? Those were the EXACT same symptoms I had, which continued after replacing all 4 ABS sensors. Turned out to be the pedal travel sensor.
    Yep, and I just retested.
    Resistance is exactly as described in this bavauto debug post, (https://blog.bavauto.com/14248/bmw-d...es-and-others/).
    That is:

    "Start the engine, and as the pedal is slowly depressed, the resistance should stay at the 250-ish ohms. As the pedal movement stops and the pedal is pressed harder, the resistance will go up to a maximum of about 1000 ohms. When installed in the vehicle and performing this static test, you will likely not be able to push the pedal far enough to reach the 1000 ohm threshold. You may only get up to around 500 ohms."

    and

    "remove the sensor (secured by a wire snap ring) and test the resistance by manually moving the plunger. You should see a steady increase from about 250 ohms up to about 1000 ohms and then at about 2/3 compression of the plunger, the resistance should go to a full open circuit (infinity ohms)."

    I also tested the wires from the pedal sensor to the ABS computer, and they tested good.

    Although.....the resistance went to full-open at 'only' 1" travel of the plunger. Hard to believe that'd be the issue?
    Last edited by aeronaut; 06-03-2017 at 05:16 PM.

  16. #41
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    The strangest thing...I can not seem to replicate this on the street. I haven't had the opportunity to get above 80mph then brake hard, but still. Accelerate to 60mph, hard braking, and ABS obviously kicks in, car squirms, modulate a little, and slow rapidly. Repeat. All ok. I'll likely have a chance to get above 80mph tomorrow, and see what happens.

  17. #42
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    +1 pedal sensor

    My friend and I both had the same ABS symptoms 5 or so years back. Both were early (4/94) '95 M3s. No ABS codes, wheel sensors checked OK. ABS light would go on. When reset, ABS light stayed off on the street for weeks. Came back on track. When ABS activated on track it caused a severe turn to the left (locked front left?), of course in heavy braking zones at the end of straights. We both had agricultural expeditions.

    New pedal travel sensor, with the correct colored cap fixed it. Apparently, there can be cracks in the circuit board inside that will lead to intermittent failures. For $80 or whatever it cost then, it wasn't worth trying to reflow the board or see what was wrong.

    Kind of like your cracked wheel sensor, it might only exhibit under stress.

    Nice recovery, by the way.
    Dave

    '87 M6, '95 M3, '04 325XiT. '15 328XiT


  18. #43
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    Quote Originally Posted by arctic745 View Post
    My friend and I both had the same ABS symptoms 5 or so years back. Both were early (4/94) '95 M3s. No ABS codes, wheel sensors checked OK. ABS light would go on. When reset, ABS light stayed off on the street for weeks. Came back on track. When ABS activated on track it caused a severe turn to the left (locked front left?), of course in heavy braking zones at the end of straights. We both had agricultural expeditions.

    New pedal travel sensor, with the correct colored cap fixed it. Apparently, there can be cracks in the circuit board inside that will lead to intermittent failures. For $80 or whatever it cost then, it wasn't worth trying to reflow the board or see what was wrong.

    Kind of like your cracked wheel sensor, it might only exhibit under stress.

    Nice recovery, by the way.
    Thanks, wish I had in-car vid for the fun of watching my arms flail.

    Ok, so that's 3 folks stating the exact same symptoms, and the same solution; pedal travel sensor.
    Oh why not, I'll order one.

    Thanks for all the help folks. Again, I'll update as I learn more.

  19. #44
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    I've resoldered every one that's tested bad on GT1. Never had to buy a new one.

    Don

  20. #45
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    Just watched the video. Nice drift entry into T5!

  21. #46
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    Quote Originally Posted by OCRentAPopo View Post
    Just watched the video. Nice drift entry into T5!
    Thanks!

    As you know, T5 is a LOT of fun with heavy and late trail braking....except when your back-end locks up at 50% braking capability!

  22. #47
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    Update. No joy. Replaced ABS computuer with used, replaced brake pedal travel sensor with new.
    Symptoms continue to piss me off.
    Will be hunting down a used ABS pump I guess.

  23. #48
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    You can rewire the pump with actual wires, fairly easy and straight forward if you trace the connections on a piece of paper

  24. #49
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    I may end up trying that. I'm having no luck finding a used or rebuilt one of the same part number.

  25. #50
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    Quote Originally Posted by aeronaut View Post
    I may end up trying that. I'm having no luck finding a used or rebuilt one of the same part number.
    I have one i have rewired. Would be willing to send to you to try out if you have the same 3 channel 95 m3 abs pump. It is sitting spare in my garage, and if it works for you would just ask you to send me back your old one in case i need one (can rewire it if i ever need it).

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