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Thread: Mk60 ABS diagnosing a locking wheel

  1. #1
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    Mk60 ABS diagnosing a locking wheel

    Hello,


    I installed a Mk60 system last year and the system worked flawlessly for three events and half way through the forth event the right front tire was locking uncontrollably when applying the brakes. The pedal did feel a tad bit softer than normal, but it was not alarming at all. Because only one tire was locking the car wanted to spin around the locking tire. Unfortunately I did not have the fault light installed at this time so I do not know if the ABS was turning on the fault light. I do have a laptop with INPA so I was able to log in and read the codes and saw one about a pressure sensor, but when I logged in later to write it down the code was not there. I do not know if the pressure sensor code was old or not. I packed up and went home and the car was undrivable.


    I let the car sit for a few weeks then brought it to a parking lot and slammed on the brakes ten times and the ABS was working fine again. I could not get it to lock. I did install a fault light and it was obviously not on because everything was working fine. When I installed the system I did install a "power switch" to the Mk60 module for testing purposes. When I turn off the ABS system the fault light turns on as expected and when braking hard BOTH front tires lock at exactly the same time which is a different outcome than when the system was malfunctioning and only the right front was locking.


    My questions are:

    1. When the system has a fault and is disabled, the ABS fault light is supposed to turn on and the ABS is completely turned off, correct? So if you slam on the brakes with the light on, the brakes will lock, correct?
    2. If there is a ABS valve or solenoid issue and one tire is allowed to lock, can the computer see that wheel is locking and throw a fault? If it sees one tire locking will the system shut off completely? It was very dangerous having one tire locking as the car wanted to spin.
    3. What if the ABS is working fine and there is a mechanical failure like a sticking caliper or a cracked rotor that is mechanically locking a wheel, will the computer see the locking wheel and shut off the ABS so at least all the tires lock at the same time?
    4. I think I either have a mechanical brake failure (but nothing is obvious) or the ABS pump has a bad valve or something related to the right front. Either way it was disappointing that I cant replicate the issue again and I have no codes. I am uneasy to compete in the car at this point and have no idea how to diagnose this intermittent problem. I wish I could just throw in a new MK60 pump for piece of mind, but they are insanely expensive.



    Any insight is appreciated.

    Last edited by bimmerbumm193; 07-20-2021 at 11:22 AM.
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  2. #2
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    I only have opinions and a bit of understanding to add.

    1) My understanding, the fault light only reports a small subset of errors. I've read, wheel sensors and ABS off, and that's all. All others are reported via CAN.
    2) I think it's possible that for any reason a wheel locks while the ABS is trying to regulate it, ABS will eventually record a fault. There may be a time lapse, or multiple events needed?
    3) See #2
    4) I believe ATE, and others, sell rebuilt solenoid units. I *think* you could also buy a MK60 for most any car and transfer the solenoid unit to your ECU. Some of the used MK60s for VWs etc can be much cheaper than the E46 M3 unit.

    Sorry I can't be of more help.

    - - - Updated - - -

    Oh, one more thing. I don't use INPA, but use one of the Foxwell BMW diag tools. (Usually around $150).

    Using those, you can run service tests that activate the ABS solenoids per wheel, and show wheel speed per wheel, and show line connection per wheel, etc. I'd think the INPA routines would be available for that also. Might give you a clue as to what's happening.

  3. #3
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    Do you have a brake bias valve installed? Is there a chance the ABS was just inop and the right front tire was just the first one to lockup or was the ABS pulsing through the pedal while the front right tire was locked up? Why was the car "undrivable" - Was this just due to the ABS being inop or did you try to pull ABS fuse/relay and go back out with the ABS inop to see if the lockup situation improved?

    I would try driving without ABS if this happens again to see what happens with the ABS turned off. It is typically a rear wheel that becomes unloaded with the ABS inactivated and is the first to lockup based on my experience but if you have a bias valve installed that may change this up a bit. Just some talking points to help think this through.

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    Quote Originally Posted by olemiss540 View Post
    Do you have a brake bias valve installed? Is there a chance the ABS was just inop and the right front tire was just the first one to lockup or was the ABS pulsing through the pedal while the front right tire was locked up? Why was the car "undrivable" - Was this just due to the ABS being inop or did you try to pull ABS fuse/relay and go back out with the ABS inop to see if the lockup situation improved?

    I would try driving without ABS if this happens again to see what happens with the ABS turned off. It is typically a rear wheel that becomes unloaded with the ABS inactivated and is the first to lockup based on my experience but if you have a bias valve installed that may change this up a bit. Just some talking points to help think this through.
    Excellent ideas!

  5. #5
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    Following, I had a couple single-wheel lockups a few weeks ago at Sonoma with my Mk60 setup.

  6. #6
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    Aeronat and Olemiss thank you for the insight.

    -I do not have any bias controller, the system is 100% stock E36 M3 calipers and plumbing with just the Mk60 installed with E46M3 master cylinder.

    -When I said the car was undrivable when the right front was locking up, I meant that for 5 turns in a row the front right tire was locking and the car was trying to rotate around the locking tire. There is no way the car was raceable in that condition. The first time it happened the car was completley sideways and almost ended up in the trees.

    - When I disable the ABS with the power switch to the Mk60 unit the car locks both front tires very evenly and easily and I dont think you could even race it in that condition either. Is there something about the E46 master cylinder bias when installed in the E36 that makes it so front biased?
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  7. #7
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    Yea, both the E36 and E46 have a lot of rear (edited) bias with the OEM setup. They depend on the ABS. If you want to run without ABS, you'll definitely want a bias valve.
    These cars are tough to run without ABS, with stock bias, and with stock booster, especially if you trail brake a decent amount.
    Last edited by aeronaut; 07-22-2021 at 08:40 AM. Reason: changed "front bias" to "rear bias"

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    Strange. That was not my experience at all with the stock e36 m3 system. It was ALWAYS one unloaded rear tire that would lockup on me when running without ABS. Got pretty good at driving without it but it took 3 plus years of horrible braking performance to get there.

    Must have some serious front bias in the e46 system if its locking up the tires getting fully loaded by weight shifting during the braking zones.

    OP,

    Definitely recommend a bias valve in the cabin to help you tune if ABS goes down. It takes a lot of practice to drive without but worth it if it keeps you on track considering how fickle e36s seem with regards to the aged ABS systems.

  9. #9
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    Quote Originally Posted by olemiss540 View Post
    Strange. That was not my experience at all with the stock e36 m3 system. It was ALWAYS one unloaded rear tire that would lockup on me when running without ABS. Got pretty good at driving without it but it took 3 plus years of horrible braking performance to get there.

    Must have some serious front bias in the e46 system if its locking up the tires getting fully loaded by weight shifting during the braking zones.

    OP,

    Definitely recommend a bias valve in the cabin to help you tune if ABS goes down. It takes a lot of practice to drive without but worth it if it keeps you on track considering how fickle e36s seem with regards to the aged ABS systems.
    OH CRAP, I wrote that WRONG. Fixed above. My experience is the stock 36 and 46 have a lot of REAR bias. Sorry. The rest of my comments in that post are correct. UG.

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    Which is why its so strange that the OP is having FRONT wheels lockup when ABS is inop.

    OP, what pad compounds are your running? Are you running the same compound F/R? That points at something amiss with your rear brake circuit if you are able to lockup both fronts wheels with ABS inop as the rear should lockup TWICE as fast as fronts on an e36 with the weight transition involved.

  11. #11
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    Quote Originally Posted by olemiss540 View Post
    Which is why its so strange that the OP is having FRONT wheels lockup when ABS is inop.

    OP, what pad compounds are your running? Are you running the same compound F/R? That points at something amiss with your rear brake circuit if you are able to lockup both fronts wheels with ABS inop as the rear should lockup TWICE as fast as fronts on an e36 with the weight transition involved.
    I think I just figured it out. A stock E36 M3 has a master with the same bore front and back, the E46 M3 master I installed with the MK60 has 25MM bore for the front and 22mm for the rear. So when the ABS is inoperable I have way more front brake bias than stock. But it is common practice to install the e46 master when installing the Mk60 system, but I guess its just so reliable that nobody has encountered this issue yet when it stops working??

    I have PFC 08 pads front and rear. The braking on the car was always stellar, pre and post Mk60 install.

    I am going to an AutoX this weekend to see if I can get the issue to happen again in the safety of a parking lot instead of at high speeds in the woods at a hillclimb

    I personally feel the ABS was working on three wheels and the four wheel solenoid was getting hung up, but it wasnt enough to trip a code. I might be able to do what Aeronat suggested and get a replacement solenoid unit.
    Last edited by bimmerbumm193; 07-22-2021 at 05:04 PM.
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  12. #12
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    Awesome. I would venture to say no one mentions it because it is MUCH better to have the fronts lockup than the rears. If the rear wheel locks up, almost instant loopage.

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    Hmmm. FYI, a smaller M/C will move bias to that axle.
    Although, the math for M/C's on a common piston rod, is a bit different.

    - - - Updated - - -

    Quote Originally Posted by olemiss540 View Post
    Awesome. I would venture to say no one mentions it because it is MUCH better to have the fronts lockup than the rears. If the rear wheel locks up, almost instant loopage.
    Very true, rear lockup first is pretty damn scary.

  14. #14
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    [QUOTE=aeronaut;30707990]Hmmm. FYI, a smaller M/C will move bias to that axle.
    Although, the math for M/C's on a common piston rod, is a bit different.

    Oh man this makes my brain hurt...let me know if my logic makes sense.
    - I started with a tandem cylinder that had 25mmF/22mmR and replaced it with a tandem 25/25.
    - increasing the rear bore means less brake pressure to the rear for the same distance traveled with the pedal
    - Since this is a tandem piston setup and the front and rear are locked together the result is less brake pressure on the rear

    So this makes sense as to why my car locks the fronts first, where a stock 25/22 m3 locks the rears first....right?

    - - - Updated - - -
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  15. #15
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    As an update on my end:

    My issue seems to have been resolved, as well as fixing an inconsistent feel pedal, after tightening a loose clamp on the vacuum line to the brake booster. Tightened, fixed apparent vac leak, and now the brakes and pedal are very consistent with no lockups.

    Not sure if that helps the OP or anyone else, but just wanted to close the loop for my issue.

  16. #16
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    [QUOTE=bimmerbumm193;30715232]
    Quote Originally Posted by aeronaut View Post
    Hmmm. FYI, a smaller M/C will move bias to that axle.
    Although, the math for M/C's on a common piston rod, is a bit different.

    Oh man this makes my brain hurt...let me know if my logic makes sense.
    - I started with a tandem cylinder that had 25mmF/22mmR and replaced it with a tandem 25/25.
    - increasing the rear bore means less brake pressure to the rear for the same distance traveled with the pedal
    - Since this is a tandem piston setup and the front and rear are locked together the result is less brake pressure on the rear

    So this makes sense as to why my car locks the fronts first, where a stock 25/22 m3 locks the rears first....right?

    - - - Updated - - -
    If you were using a balance bar, yes. But a balance bar ensures the input pressures to both M/C's are the same. A dual piston/single-rod M/C doesn't keep the input pressure the same like a balance bar, it keeps the travel distance of the pistons the same. So I'm not sure. I need to draw this out, and create a model. I'd love to add this option to my M/C brake-bias spread sheet.

    Bottom line, if that's what you changed, and that's what happened, you have your answer. (How's that for a cop out. )

  17. #17
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    Quote Originally Posted by mslevin View Post
    As an update on my end:

    My issue seems to have been resolved, as well as fixing an inconsistent feel pedal, after tightening a loose clamp on the vacuum line to the brake booster. Tightened, fixed apparent vac leak, and now the brakes and pedal are very consistent with no lockups.

    Not sure if that helps the OP or anyone else, but just wanted to close the loop for my issue.
    Thank you for updating us and glad you fixed it.

    UPDATE on my end also. I have done three events so far and no lock ups. The only thing I did was rebled the brakes.
    So as a recap....I installed the mk60 early last year, did two events, parked it for winter and DID NOT bleed it before this season started since it only had two events on it (but it did sit over winter). Then I did one event in the spring and it worked great, then on my second run at the second event it locked up for 5 corners in a row. I wonder if it is really that sensitive to fresh fluid and bleeding? I did remove and reinstall the vacuum hose that fixed your problem...but I didnt see any issues.
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  18. #18
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    Very odd. Maybe, maybe, there was air in one of the lines, causing one of the pressure sensors to read significantly different than the other, confusing the ABS.

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