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Thread: '87 K75s Front Brakes . . .

  1. #1
    Registered User kentuvman's Avatar
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    '87 K75s Front Brakes . . .

    I've experienced and read about the pulsing front brakes on the "S" model.

    I've read Don E.'s threads on all he did to resolve the problem.

    I've gone down the same path as Don - replaced the front wheel bearings, installed EBC floating rotors & EBC HH brake pads - the dang front brakes still pulse & shutter when trying to use the front brake by itself while coming to a stop. The use of both brakes diminishes the problem.

    I do have a reference point but to make a change will be expensive . . . my R65LS had a brake rotor conversion from Spiegler Performance - I learned about this when interviewing the owner and writing a brake story for MOA. The front brakes on the R65LS are also dual and work so smoothly I could sing about it! The other thing - the EBC rotors will start to build up rust on the surface, even in the garage - when I rode it out to CA and left it covered for a couple weeks, corrosion had formed and I used 0000 steel wool to remove it - the Spiegler rotors don't do that.

    Realize the front fork engineering/ geometry is different between the R65LS and K75s

    Aside from this issue, I like the bike so much, I want to solve this problem - the next step is to have Spiegler convert my original rotors - the only problem is . . . I tossed the old rotors in the trash can after installing the EBC's - I did feel some improvement at first.

    I've spoken with other K75s owners - one guy I met at a rally this weekend said his used to do it but not anymore - and he's using the stock OEM BMW rotors.

    The input I'm seeking from you is: am I chasing a dream here or is the pulsing here to stay? My axle is straight and the steering head bearings don't bind in any way. I believe my front wheel is balanced, as I've ridden over 90 without any signs of out of balance.

    If consensus says give the Spiegler rotors a try, I'll need to purchase a set of used K75 rotors, as they need the hubs to do the conversion - would a set like these work?
    http://cgi.ebay.com/ws/eBayISAPI.dll...tchlink:top:en

    Want to figure this out.
    Ken Tuvman
    Excelsior, MN
    K75s, R65LS, R60/5

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    Registered User kentuvman's Avatar
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    Update

    I've been running the Bridgestone BT45's on the K and while I like them, they wear fairly quickly.

    I received a new set of ME880's today. Discovered the front tire size of the BT45 is 100/80-18

    The front tire spec in the BMW owners manual is 100/90-18 which means I've ran the incorrect size for the past 15k miles. Not sure this will make any difference but interested to find out when I get the new tires installed.

    Also discovered, after looking at my receipt, the EBC rotors I purchased are MD604's which correspond to a K100Rs - according to another website, the correct rotor is the MD611

    The tech support person at EBC is back from vacation on Thursday - I'll give him a call and try to sort this out. I still like the Spiegler conversion rotors better.

    Before I roll the dice on another set of rotors, I want to be sure I know the source of the problem! A great bike - just trying to make her a little better!
    Ken Tuvman
    Excelsior, MN
    K75s, R65LS, R60/5

  3. #3
    Mars needs women! 35634's Avatar
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    Running 100-80's shouldn't cause pulsing. Have you checked the rotors for lateral runout?
    1987 K75S
    Original litter
    Original owner
    2012 Ural Gear Up

  4. #4
    Registered User kentuvman's Avatar
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    Quote Originally Posted by 35634 View Post
    Running 100-80's shouldn't cause pulsing. Have you checked the rotors for lateral runout?
    No - sounds like a good suggestion - how would I does one do that?
    Ken Tuvman
    Excelsior, MN
    K75s, R65LS, R60/5

  5. #5
    Registered User kentuvman's Avatar
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    Probably like starting an "what kind of oil thread is best" . . .

    I've been reading about pulsating brakes on certain model BMW bikes and mine qualifies - since I can safely stop the bike, I'll probably just put up with the nuisance - it's really a shame I can't figure it out - but I haven't seen anyone else who can either . . .

    Found this familiar story:

    My this sounds familiar. The K75S is also prone to this sort of problem. Bad enough that people have sold their bikes after going through 3-4 sets of very expensive rotors. I had the problem with THE K75S..

    I tried Braking rotors (mount to the stock centers) - worked for a while, then the problem was back.

    I tried good used BMW rotors - worked for a while, then the problem was back.

    I tried honing the brake disks with a brake hone. Made no difference.

    I tried new wheel bearings (on the advice of a sagely BMW mechanic) - - worked for a while, then the problem was back.

    I tried new wheel bearings a second time - it made no difference, problem remained. I checked the wheel for out-of-round and out-of-plane - it was perfect.

    I tried more aggressive pads in the hope they would wear off any munge sticking to the disk and make the problem go away. They made no difference, problem remained.

    I even tried having a set of rotors Blanchard ground (a double-sided grinder - sort of what is done when they're manufactured.) It made it MUCH worse - unrideable actually.

    I finally put on a set of EBC rotors and EBC pads. They are still on the bike and the current owner reports no problems. Is that the answer? Perhaps, but the current owner doesn't ride it as much as I did, so it may just not have hit the mileage needed to trigger whatever is causing it.

    I share your pain. In no case did the rotors measure out of specification. There was no discernible play in the wheel bearings and no roughness. The calipers weren't dragging. I was not a super aggressive rider - and rarely did any full-on braking.

    I can imagine BMW is as puzzled as I was as to the real cause.

    I sent one rotor away to a friend at the University of PA Metallurgical Department. They did a surface analysis of the rotor surface and found spots on it - shaped like a brake pad - where the actual composition of the stainless rotor had changed. I attributed this to instances where I had washed the bike and put it away wet (without riding it..) and later found the pads rusted solidly to the rotor (requiring some force to break free.)

    The EBC rotors I put on were a high-carbon steel, not a true stainless steel. They don't seem to rust, but they also are probably a better match for braking purposes.

    Pisser isn't it? Like I said - I feel your pain.
    Ken Tuvman
    Excelsior, MN
    K75s, R65LS, R60/5

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