‘Pulsing’ front brake at slow speeds - BMW F800 Riders Forum & Registry



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  1. #1
    nsseverson's Avatar
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    Hey there fellow f800 riders, I have a 2014 GS that I recently inherited. I’m noticing that when coming to a low speed stop (intersection or a stop sign) the front brake and lever seems to pulse. What I mean by that is it seems to vary slightly in pressure in the lever as well as braking in the front wheel but in a repetitive fashion that is slow.

    I’m not a brake expert, and unfortunately most shops are closed during this quarantine - but how does a novice wrencher (On a new bike to me) verify what’s going on here?

    FYI the brake fluid in the front reservoir is very slightly milky, so I’ll be bleeding that and putting new fluid in later this week. That wouldn’t cause pulsing would it? I examined the front rotors but they look fine - albeit not sure what I’m looking for.

    Your help is greatly appreciated.



    Nick
    Venice, CA 

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  3. #2
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    potentially it could be the ABS pulsing the brake as it thinks you're locking up (especially at lower speeds) check the ABS ring located on the wheel is clean and free of any dirt, mud or other items it could mistake for one of the reading marks.
    BMW F800ST, 2010, Black, Fuzeblock, Sat Nav, BMW Tank Bag, Givi Touring Screen, 

  4. #3
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    Start with flushing the fluid like you're planning, what you're seeing is extreme water contamination in the brake fluid. That contamination 'could' be causing your problem due to the way water compresses more easily than brake fluid. I'd run a full bottle through the front, and then a reservoirs worth from a second bottle. Use the rest of the second bottle to do the rear brake. Pro tip, use a syringe to empty the reservoir then refill with fresh fluid before flushing. No need to push known bad fluid through.
    Next I'd check wheel bearings, check them for smoothness and check to see if the wheel has any play. If that fails, then the next step would be check the rotors for warping. Easiest way to do this is with a dial indicator to check for runout. Don't worry about spending big bucks here, a cheap harbour freight setup will be fine and should cost less than $40.

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  7. #4
    AKBeemer's Avatar
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    I recommend checking the runout on the rotors first. Easy to do and the most likely suspect; in your case it sounds like one of the front disks is the problem. If you do not own a dial indicator, then they are fairly inexpensive at Harbor Freight, or watch this video: https://www.youtube.com/watch?v=Jf27EI93f74
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    I dont know what tools do you have at home but you could block somehow one of the front brakes at a time an see if the pulse is related to one of them or not

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    I seem to have this problem every 10K miles or so on my F650GS. The rotor was not warped. I believe the pulsing is the result of friction pad material building up on the brake disc. Try cleaning the disc with a Brillo pad, then brake cleaner, followed with denatured alcohol to clean off any remaining deposits. Give that a try before doing anything else. On my bike that works for a while, but eventually I will need to replace the disc with a new after-market one. You can also remove the brake pad and sand it a bit to remove any glazing and then reinstall the pad.
    Richard - Current bikes: 2016 BMW R1200RS, 2018 16.6 kWh Zero S, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2005 Triumph T-100 Bonneville, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior. 

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  12. #7
    nsseverson's Avatar
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    Thank you all for you’re replies! I’m going to start with the fluid and also clean the disks - unfortunately my management company is telling me I cannot do ANY work in my garage... they caught me right in the middle of lubricating my chain.... THE HORROR. I’ll just to the rest with a closed garage door.... and a respirator haha



    Nick
    Venice, CA 

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  14. #8
    notacop is offline The original Schwartz Wald Troll
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    Can't blame the management really. So mechanics like to clean with gasoline and sometimes things go boom. Closing the garage door can help some if you aren't too loud.
    A friend and I used to hide in my garage when working on projects. Somehow another neighbor got blamed for all the noise we made.
    Gawd, hadn't thought of that in years, thanks for the giggle!

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    Nick. This problem came up in the f800GT forum a week or so ago and has been mentioned several times over the years. I also had this problem (on a GT). Firstly, and without wanting to offend other posters, it is most unlikely to be a warped rotor. Not sure about the GS but ours have "floating" discs. This allows for better heat dissipation (meaning you would have to be braking hard repeatedly to get them hot enough to warp) and also allows for a very slight amount of warpage, because they"float" on bobbins. After trying most of the remedies suggested I found that cleaning the sensor rings, as suggested by DJ123, with denatured alcohol (front and rear) cured the problem. Don't know why this would be so as they looked perfectly clean to me to start with and didn't look much different afterwards. Try it, as it only takes a minute or two.

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    On my 2010 F650 GS, moving from BMW front rotor and pads to an EBC front rotor and pads eliminated the recurring issue I was having with pulsating front brakes. I had the same pulsing problem with two BMW rotors. The problem has not returned since moving to the EBC parts. It may be a coincidence, but if I do have to replace the front rotor again I will stick with the EBC.

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    I should have added to my response a week ago that I also switched to an EBC rotor and HH pad and have not experienced the pulsing problem since then.
    Richard - Current bikes: 2016 BMW R1200RS, 2018 16.6 kWh Zero S, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2005 Triumph T-100 Bonneville, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior. 

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    Redned: What are the sensor rings?

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    Thank you Richard230, for saving me the trouble of making a similar comment. The only difference I would add is do NOT use a Brillo pad (steel wool), but instead use a 3M ScotchBrite pad.

  22. #14
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    Quote Originally Posted by Selden View Post
    Thank you Richard230, for saving me the trouble of making a similar comment. The only difference I would add is do NOT use a Brillo pad (steel wool), but instead use a 3M ScotchBrite pad.
    Sorry, You are correct. I thought a Brillo pad was one of those plastic-wool scrapers. I think I got the brand mixed up with the 3M pad. I stand corrected. It has been a while since I bought a pad like that and the Brillo name just stuck in my mind.
    Richard - Current bikes: 2016 BMW R1200RS, 2018 16.6 kWh Zero S, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2005 Triumph T-100 Bonneville, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior. 

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    Jim. The sensor ring is the slotted metal ring fitted just below the rotor mounting bolts. It has many slots and "lands" around its circumference. This allows the magnetic sensor to calculate the rpm of each wheel and compare them. If there is a difference in rpm, the ABS assumes one wheel has locked up and and is activated. As it is magnetic and the slots are fairly large, I don't how my cleaning of them could make any difference....but it did.

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