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Thread: 1992 K75S front brake rotor interchangeability

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  1. #1
    broadstone
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    1992 K75S front brake rotor interchangeability

    I recently took delivery of 2 used but in excellent condition front rotors from a 1991 K75 to replace the very rusted ones on my as-is purchased 1992 K75S. The seller assured me that the 91 and 92 rotors were the same but in looking at them side- by- side there are a couple of visual differences. On my 92 the discs are secured to the mounting plate with bolts; the 91 uses rivets. Also, the 1991 rotors are a couple of thousaths of an inch thinner. Before I pull off the front wheel can anyone tell me if they are interchangeabl or provide any other info that could be helpful? Thanks

  2. #2
    A bozo on the bus deilenberger's Avatar
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    Sounds as if your '92 rotors have been replaced by a former owner.

    From the factory - the disk is riveted to the rotor-hat-center. Aftermarket solutions like "Braking" rotors require you to grind the rivets off, then bolt a new stainless disk to the old rotor hat. My WAG - that's what you're looking at for the old ones. The fact that they're "very rusted" makes me think plain-steel rotors, which are not necessarily a bad thing on this bike.

    Have you ridden the bike to see if the rust will scrub off with use?

    The problem with the factory stainless rotors - brake shudder. It's a much too common problem on the S. I know of at least 3 people in my local club - including me - who got rid of their S bikes because of this. (Why just the S is beyond me - but the pattern was fairly clear, it happens a lot more with S bikes then any other klassic-k.)

    I went through about 5 sets of rotors on my '87. Finally got EBC replacement rotors, and it seemed to solve the problem (the current owner of the bike hasn't reported any problems.) Something about the S geometry makes it very sensitive to friction variances on the rotors. The EBC rotors have a higher carbon content then plain stainless steel, and for some reason that seems to help.

    Suggestion - try using the brakes as is for a bit. They'll be grabby to begin with, but as the rust wears off - they should smooth out. If used regularly and stored inside the rotors will generally look OK, and given the choice between rust and shudder - I'll take the rust any day.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  3. #3
    broadstone
    Guest

    K75 brakes

    Thanks, Don. The braking on this bike with the rusted rotors is very rough (kind of rough and grabby). I've ridden it for about 50 miles and, although the rotors have become a little more shiny, the braking remains uneven and rough. Because it looks like their the 91's are compatible, I'll try installing them and see if the braking improves. I'm still concerned about the possibility of partially frozen slave cylinder(s) but ill get to that next.

  4. #4
    BMW uber alles! Zagando's Avatar
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    Don't know if this will help you, Jim but my stock stainless rotors got a bit rusty when I was in rainy Hawaii and didn't ride so much. Some CLR and green Scotchbrite pads worked wonders on the rust and after riding regularly therafter they're fine (and thank goodness no shudder as of yet).
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  5. #5
    broadstone
    Guest

    K75S brake rotor

    Thanks for the better description; "shudder" describes it well. Anyway, I have to pull the wheel to clean the ABS counter disc and the inside surface of the rotors so I may as well use the "new" ones because they are like new. Surprisingly, the pads look good and the rear brake is fine. Jim

  6. #6
    3 Red Bricks
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    Recheck the gap to the ABS sensor when you change the rotors.


    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

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