bmw r1200gs lc rear brake failures

Discussion in 'GS Boxers' started by grace, Oct 31, 2017.

  1. pistole

    pistole Long timer

    Joined:
    Jan 11, 2013
    Oddometer:
    2,338
    Location:
    earth
    Hi. I will share this with riders here pertaining to the updates that have occurred to the pressure modulator.

    My issue is the failed pressure modulator. Dealer has ordered that latest part number. It is the 5th iteration of that part from BMW.

    This is a known issue where I am from (at least to the dealers).

    Once resolved I will update.

    Thank you all

    Attached Files:

    Motorius likes this.
  2. dirttransitions

    dirttransitions Been here awhile

    Joined:
    Oct 4, 2017
    Oddometer:
    208
    Location:
    Athens oh
    hope that works for you!!!
  3. Frog_1976

    Frog_1976 Adventurer

    Joined:
    May 6, 2020
    Oddometer:
    10
    Location:
    The Netherlands
    Yesterday I was redeay to go, to make some logging, but at the point of driving off the alarm of the rear wheel pressure came on.
    But to give you a idea off how the logging will look, I attached picture.
    (Don't know how I would be able to attach a CSV file).

    It's not much, just a drive out the garage.......... adn back down again :-).

    Will fix the tire, and give it a other try soon.

    Greets


    André
    logging brake module.PNG
  4. Frog_1976

    Frog_1976 Adventurer

    Joined:
    May 6, 2020
    Oddometer:
    10
    Location:
    The Netherlands

    Hope this will solve the issue for you.

    Is this still a warrenty case, (its not like the paint is comming off) it's a real safety issue?

    Kind regards


    André
  5. JimsBeemer

    JimsBeemer 2017 R1200GSA, 2016 R1200RT Supporter

    Joined:
    Jan 4, 2014
    Oddometer:
    743
    Location:
    San Jose, CA
    That would have been me, and thanks! Very helpful in the discussion.
    Jim
  6. pistole

    pistole Long timer

    Joined:
    Jan 11, 2013
    Oddometer:
    2,338
    Location:
    earth
    Update.

    1. It's not the brake reservoir (duh).

    2. It's not the rear master pump (duh also).

    3. It's not the type of brake fluid (x2 duh).

    4. It's not how you bleed or how many times you bleed (ok duh).

    5. It's a failed pressure modulator aka ABS pump which has been updated 5 times in part numbers since the LCGS came out.

    .

    Log your complaints with bmw and request the latest part number for the ABS pump.

    Ok. Done
    Motorius and Candubrain like this.
  7. Sailorlite

    Sailorlite Long timer Supporter

    Joined:
    Feb 18, 2006
    Oddometer:
    1,289
    Location:
    Seal Beach, CA
    Ok. Done for you maybe. But in my case the dealer, after numerous BMW-guided attempts to fix, yesterday replaced the rear master cylinder.
  8. Hypersonic

    Hypersonic OnTheRoadAgain

    Joined:
    Jul 14, 2015
    Oddometer:
    67
    Location:
    GREECE
    What if the bike is out of warranty?
    Solo Moto likes this.
  9. sizzlingbadger

    sizzlingbadger Been here awhile

    Joined:
    Jan 28, 2013
    Oddometer:
    517
    Location:
    New Zealand

    So how come the latest bikes with the latest ABS pump still have this issue ?
    18415, Motorius and Pch123 like this.
  10. pistole

    pistole Long timer

    Joined:
    Jan 11, 2013
    Oddometer:
    2,338
    Location:
    earth
    34519444398
    Pressure modulator
    From: 01/01/2019
    To: -
    Price:
    Supersedes:
    34519898518 (08/01/2018 — 04/11/2019), Exchangeable retrospectively
    34518566956 (07/01/2016 — 07/26/2018), Exchangeable retrospectively
    34518561705 (08/01/2015 — 09/24/2018), Exchangeable retrospectively
    34518554180 (04/21/2014 — 12/18/2015), Exchangeable retrospectively
    34518549461 (08/01/2013 — 05/21/2014), Exchangeable retrospectively
    34518534990(09/01/2012 — 08/01/2014)

    .

    Good question : why do the newer bikes also suffer from a soft brake ? Guessing here : perhaps your "new" bike may have an old pump.

    The above cut/paste is from realoem and shows the parts history of the pressure modulator (the number of revisions , 7 , is shocking).

    Concentrate on the latest years (ie , 16 to 18 , 18 to 19 and the new number above). See the overlap. Ie , your bike can have a build date up to 11 Apr 2019 and yet have the old pump.

    Am gonna test the heck out of the new bike now and report further. Rear brake pedal is hard , about an inch of travel at the end of the pedal.

    .

    As an aside : there was thread on the european site about air in the rear brake circuit :

    https://www.gs-forum.eu/threads/umfrage-wer-ist-von-luft-im-hinteren-bremskreis-betroffen.153022/

    interesting reading.
    sizzlingbadger likes this.
  11. Frog_1976

    Frog_1976 Adventurer

    Joined:
    May 6, 2020
    Oddometer:
    10
    Location:
    The Netherlands

    Hello Pistole,

    Good to hear it's fixed for you, must be a relieve to know you can trust your rear brake again.
    You sayed in the biginning you did'nt trust the ABS module / pressure modulator, and you were spot on :-).

    Can you maybe explain a little bit more on how the failure mode exactly works?
    I am still curiuos on how it's possible that air gets into the system without loosing fluid?
    And I still like to know if there is a propotional valve in the circuit, or if it used the pump to activate the rear wheel?

    With kind regards

    André
  12. pistole

    pistole Long timer

    Joined:
    Jan 11, 2013
    Oddometer:
    2,338
    Location:
    earth
    hi Andre.

    the reason why I suspected that ABS pump was because locally where I am at (Asia) , the dealers are well aware of the problem with the rear brake & repeated bleedings. Without even telling me to bring in my bike for diagnosis , when I described the problem to the dealer's technician , he ordered the pump for me straightaway. Mind , this is long past warranty and the pump is not cheap.

    as for why and what is happening in the pump : I cannot say. The tech also does not know bec they have never opened one up before to have a look.

    basic analysis :

    1. air causes the rear brake circuit to fail. How do you know this ? When you have no/soft rear brake , you bleed rear , air comes out and you get back your rear brake. No disputes here.

    2. There are no leaks in the entire braking circuit. Am not talking about the Hayes calipers on the 1250s. So no fluid is getting out. No disputes here.

    3. whatever the condition of your rear brake , the front works fine. This points to a separation between the fr and rr brake circuits, at least from a bleeding point of view. No dispute.

    4. when you have no/soft rear brake (whilst the bike is driven) , the fr to rr linking does NOT work because the pump cannot build pressure in the rear circuit. I know , I know : people here have been saying the linking still works because they "SEE" the brake actuation numbers on their on-board-computer. That's wrong. The computer "sees" the pump actuation , but there is no pressure going to the rear brake caliper. How do I know this ? When you have no rear brake , brake as much and as hard as you like using the fr brake lever and the rear caliper is COLD. If the actuation numbers are to be believed , you would have a hot rear caliper. Maybe some dispute here / Maybe not.

    5. When you bleed and get back your rear brake, try riding ONLY USING YOUR REAR BRAKE. Do not touch the fr lever. The rear does not soften. How do I know this ? I tested and could keep my rear brake as long as I didn't touch the fr lever. If I started to use the front lever , the rear dies.

    6. I was able to bleed the rear caliper whilst applying pressure to the front brake lever (engine off). Okay. Deep breath. This is supposed to be impossible , ya. We all know they are separate circuits and this is not supposed to happen. But I could do it and fluid level duly falls in my FRONT master reservoir. Note : I was only able to do this a few times and eventually (a) could not repeat it anymore and (b) it caused my abs error light to come on, intermittenly.

    7. ABS error light : whatever the condition of your rear , the abs light does not come on. Ie , the system cannot detect a total failure in the rear pressure circuit. How do I know this ? Well if you have no rear brake and the ABS doesn't know anything about it , it obviously does not test for it.

    8. ABS front works whatever the condition of your rear brake. ABS rear does NOT work when you have no rear brake (duh).

    9. Eventually , from a deduction process , you can tell where this is going. The problem is a linking issue in the pressure modulator. Understand that the linking is done by the pump. When you squeeze the fr lever , your hand pressurises the front calipers , but the pump actuates the rear circuit. When you step on rr brake pedal , your foot pressurises the rear caliper , not the pump. Linking if Fr to Rr. Never Rr to Fr.

    10. But why does the linking cause the rear brake to fail ? I don't know. I can guess though. How the rear is pressurised by the pump is probably done in pulses (think fuel injector). Ie the pump builds and accumulates pressurised fluid in the unit. When called upon to pressurise the rear , the electric solenoids (there are many in the unit) actuate to flow pressurised fluid to the rear circuit. As for how it controls how much pressure to go to the rear , I don't know. If definitely does not know how much pressure there is in the rear circuit (because if it did , it would throw an error when your rear brake dies on you). It may be working on a set algorithm , eg , pulse rear X number of cycles when front circuit pressure is Y. Guessing here , sorry.

    11. Long story short , the linking function is causing air to build in the rear circuit.

    12. We come full circle now : where does this air come from ? The chap selling the rear reservoir mod is , sorry , not the solution. The rear brembo master is also , sorry , not the solution. Type of brake fluid = no. High temp fluid = no. Low viscosity rear fluid = no. Hang 20 kgs on your rear pedal overnight = no.

    13. Speculation : the method used in the pressure modulator (hence its name , its not called an "abs pump") to build pressure in the rear circuit to produce the linking effect is causing air to build/enter the rear circuit. There.

    14. I think that it is the way she pulses the fluid that causes the brake fluid to aerate. Aerate meaning that air bubbles is built in the fluid when its "beaten" by the solenoid at high frequency. How do I know this ? Go back to my point about how my rear brake survives when I only use it and not the front (ie , force the bike not to link).

    15. Now , we understand that brake fluid will only aerate when there is existing air in the container to mix with the fluid. Imagine a can of brake fluid. Say it is totally full with no air inside. You can shake it no matter how long and how vigorously and no air will be introduced into the fluid. Ie , brake fluid itself has no air in. Its the air around it that when shaken aerates the fluid.

    16. Again guessing : there is a pocket of air trapped somewhere in the pressure modulator which when the solenoid pulses causes the brake fluid to aerate thus producing bubbles in your rear circuit. This is the reason why bmw steadfastly asks dealers to jump through hoops , use / don't use the computer when bleeding , hang a weight on the rear pedal overnight , etc. BMW is trying to find and get ALL THE AIR out of the pump. Sometimes if works , sometimes it doesn't. This is evident because some bikes are okay , some suffer.

    17. The SEVEN iterations of the pressure modulator : you will notice that of all the parts on the GSLC , the part which has evolved the most is the pump. Nothing else can match its 7 revisions. Ie , there are more revisions than the bike has been around, years wise. Is this a coincidence? I don't believe is coincidences, sorry. I know that the bike has acquired things like cornering ABS and hill hold over the years. Could these have mandated pump updates ? Maybe. But probably not. Cornering ABS and hill hold was a result of multi axis inertia measurement capability and software. Ie, the IMU sensor tells the computer the bikes attitude (eg , leaned over in a corner or stopped on an incline) and the software works out what to do and tells the PRESSURE MODULATOR how to proceed.

    18. Hence again full circle : its the pump.

    19. I would like to hear people's opinion on this , if possible , since alot of it guessing , but educated guessing.

    20. thanks for reading and sorry for the length.
    D-Star-R, slipknot, Mrmerlin and 5 others like this.
  13. Frog_1976

    Frog_1976 Adventurer

    Joined:
    May 6, 2020
    Oddometer:
    10
    Location:
    The Netherlands
    Hello Pistole,

    Thank you for writing this all down, I like your reasoning.

    Like you say, it's strange the ABS module part nr is changed so many time's, BMW is not the company that changes part quikly.
    It could be that it just changed because they changed brand/supplier, but still, not a commen thing to do.

    Curious if more people have it done on the LC models outside Asia, as this is the first time I hear about it being a known issue.

    Again, thanks for the write up, and test the &*^% out of the rear brake :-), enjoy the ride.

    Kind regards

    André
  14. Callisto224

    Callisto224 Long timer Supporter

    Joined:
    Jan 5, 2010
    Oddometer:
    7,387
    Location:
    Smyrna, GA
    Has anyone else confirmed Pistole's theory that the rear brake works fine if the front brakes are not used? And, if the front brakes are used, the rear no longer works?

    It would be interesting to see temperature readings of the rear caliper in both instances.
  15. Frog_1976

    Frog_1976 Adventurer

    Joined:
    May 6, 2020
    Oddometer:
    10
    Location:
    The Netherlands
    After my latest rear brake bleed, It stays firm.
    Even after 2000 km it did not changed and I use 99% of the time only the front brake lever.
    (I still use DOT 4 Lv from Kroon oil, nothing special).

    So I won't be able to test it.


    Kind regards

    André
    Callisto224 likes this.
  16. Candubrain

    Candubrain Been here awhile

    Joined:
    Jan 13, 2018
    Oddometer:
    568
    Location:
    Kincardine, ON, Canada
    I've done close to 900Kms since I hung a weight on my rear brake pedal for 2 full days, I did not bleed it afterward as the pedal stroke came back up to normal and I have not had any further issues with brake fade. I've done a mixture of off-road, gravel road and highway riding.
  17. mkccowboy

    mkccowboy Been here awhile Supporter

    Joined:
    Oct 24, 2010
    Oddometer:
    115
    Location:
    Colorado
    I’ve had rear brake issues on both my 16 and 18 GSA. By 2500 miles rear pedal would go soft. Tech at shop I work at here in Denver area was having similar issues on his 15 GS. He flushed his and my brakes and replaced fluid with Motul 600 racing brake fluid. He and I both have not had the issue to this point. I’m now over 3000 miles since fluid replacement and believe he is near same. So far we both are still good. Keeping my fingers crossed.
    Callisto224 and Candubrain like this.
  18. sizzlingbadger

    sizzlingbadger Been here awhile

    Joined:
    Jan 28, 2013
    Oddometer:
    517
    Location:
    New Zealand
    Mine takes around 4000kms to go soft, its quite a gradual process. I bled the rear again recently and use a slightly different technique to try and get the fluid to flow through faster (in the hope that any bubbles didn't have chance to float back to the high point in the system between foot-pedal pumps). Managed to get some air out of the system and the pedal is nice and hard now. Let's see how long it lasts this time.
  19. Hypersonic

    Hypersonic OnTheRoadAgain

    Joined:
    Jul 14, 2015
    Oddometer:
    67
    Location:
    GREECE
    Same situation with mine too.
    Not reached yet 900km since the 4 x 12V7Amp Pb batteries weight.
  20. Hypersonic

    Hypersonic OnTheRoadAgain

    Joined:
    Jul 14, 2015
    Oddometer:
    67
    Location:
    GREECE

    Nice post!
    No apologies for the length! We should thank you for that!!
    I can say that I agree or believe you!

    But, some brainstorming, about...

    #4. As soon as, I will have the rear soft again, I will TEST it, because I thought that rear was linked-worked, even if the pedal was soft !
    If it's not working as linked, with the pedal soft, it's not good !!!
    I will paint (permanent marker) the rear disk to see if the pads clear the color ... ??

    #5. I didn't bleed the rear (yet) but hung a load on the lever. So, I somehow pressurized the air in the rear cirquit... I rode 200-300km using Front and (sometimes) rear, but rear is still OK. Where did the air go and for how long it does not re-act
    with the fluid? I can't get used to use only rear, not even for tests! It's even hard to use (sometimes) the rear for tests!!

    #6. You say bleeding rear with -engine off- and you get later an ABS error light... Engine off but bike switch/electronics on ? I think that the ABS pump is working even if the engine is off, as long as the battery is OK. This front/rear fluid linkage on separate ( ? ) circuits has to be confirmed....

    #8. I can say >> that ABS rear DOES work when you have NO rear brake... I usually don't use rear at all, so when the time comes to use it I just realize that I don't have rear.... So I use the front and also press the rear lever all the way down and the rear ABS is working (rear wheel does not block)... OK, you can say that it works as ABS but not as pressure modulator!

    #10. Definitely agree with you...

    #16. Where have all the bubbles gone ? We have a closed circuit... I think that the brake works as the old no-ABS brakes.
    Fuild reservoir>hose>master+pedal>hose>caliper....
    As there is the ABS control added, there should also be on the ...master>a hose to >ABS unit...
    When I press the pedal, I increase the pressure in master, which sends this same pressure to the caliper AND the ABS unit...
    No matter how much force use on the brake pedal, the ABS keep the pressure where it should between the master and the caliper...
    So, the bubbles are in the hose circuit of caliper and ABS... ? And maybe close to the ABS ?
    After the weight on the pedal the bubbles are pressurized/forced back in the ABS (away from the master>caliper circuit) ?
    And the bubbles get active again when the ABS unit starts to work (fast solenoids frequency) as a real Anti-lock Braking System and not as a brake link controller ?
    Could the constant use of the rear to its limits so the ABS gets activated, makes the rear soft again, faster than normal use ? << Nice TEST ...
    pistole likes this.