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Thread: 1980 R100 front brake free play

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  1. #1
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    1980 R100 front brake free play

    I am completing a frame on restoration of a 1980 R100. I am having trouble with the front brake free play. The front wheel turn with just a little drag, as does my 1984 R100. The master cylinder cable has what I believe is the correct free play, yet I have almost no free play at the lever. The only way I can accomplish free play at the lever is to loosen the cable to the mc too much, as in the cylinder at the end of the cable isn't even touching the master cylinder lever that pushes the plunger. The mc seems to be working right as fluids exiting and returning are evident when I take off the cap and look into the reservoir. Anybody have any ideas?

  2. #2
    Sir Darby Darryl Cainey's Avatar
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    Going back from memory, there is a special feeler guage from BMW to set the proper gap so I don't think it's meant to touch.

    Hope this helps!
    Ambassador BMW MOA Ontario Canada
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    1977 R100RS, (Retired) 1993 R100GS (just getting started)

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    Administrator 20774's Avatar
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    I'm not sure if the '80 model had the under-tank M/C. If so, then as Darryl suggests, there's an adjustment at the back of the M/C to ensure that the internal piston is in the right spot. Shown here on a /6 owner's manual:

    http://www.pbase.com/dwerbil/image/74356089
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #4
    Registered User lmo1131's Avatar
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    Ref., 1.20mm = 0.047"



    Being a /5 kinda guy I don't have a master cylinder. It's hard to tell from that old B&W manual photo; mechanically what's going on here, does the "fork" fit around the machined groove (holding it in place), and the "slack" is taken up/let out with the ferrule?

    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  5. #5
    Administrator 20774's Avatar
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    My Haynes says:

    "Slacken the cable adjuster locknet and insert the forked feeler gage into the groove in the master cylinder piston. [Note: the feeler gage is 1.2mm thick.] Adjustment is correct when the feeler gage is just freee to move against the master cylinder body."

    So, if there's too much tension on the cable, it pushes the small cylindrical shaft which pushes the piston farther into the m/c body and the groove moves with it, eventually disappearing inside the m/c body. Too little tension, and the groove comes too far out. So, the free play/tension has to be just right so that the groove is near the m/c body but just near enough to fit the feeler gage into the groove.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  6. #6
    Registered User lmo1131's Avatar
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    I can see how that would be p-r-e-t-t-y hard to do without the special "feeler gauge".

    Thx Kurt.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

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