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Thread: 78 R100 front brake switch

  1. #1

    78 R100 front brake switch

    OK something new today. I was checking the front brakes on my 78 R100 and the brake switch stuck???
    You know jane, It's always something.
    Anyway I released the pressure at one of the bleeders thinking the piston might be stuck but that didn't do it so I removed the master cylinder and removed the switch and it still had continuity so doing what any alpha male would do I beat it on the side of my bike lift and it released and went open again.
    I don't want to put it back on because it will surely stick again in the near future.
    Someone PLEASE tell me there is a cheaper switch out there. A new one from a and s is 33.23 Plus shipping
    YES I AM a tightwad

  2. #2
    Liaison 20774's Avatar
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    I like stopping! And tend to want the best for those situations. But have you checked say Euro Motoelectrics?

    http://www.euromotoelectrics.com/

    Motobins in Europe is now to have good parts and usually good prices despite the cost of shipping.
    Kurt -- Forum Liaison ---> 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!

  3. #3
    '99 '03 '06 National Co-Rally Chair Friedle's Avatar
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    front brake switch

    And what are you willing to spend when your ass gets rear ended because you were too much of a tightwad to properly repair the brake switch circuit? Look at the big picture has multiple meanings on a motorcycle.

    Friedle
    Ride fast safely

  4. #4
    Thanks 20774 for the info on motobins. It seems I can get the "proper" switch from them for around 20 dollars delivered from Great Britain.
    I fail to see why paying too much for parts is a status symbol for some bmw owners.

  5. #5
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    Add some treats to the order and improve the value more, maybe?

  6. #6
    If I were you, I would bite the bullet NOW and upgrade to the handlebar master cylinder and brake switch. I tried to do use and rebuild my M/C after spending around $70 for a rebuild kit. Lasted about 2-1/2 years and started leaking again - getting on all those relays and switches under the tank. The handlebar upgrade changed everything for the better!

    Just sayin......
    "The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers

  7. #7
    Rally Rat 1074's Avatar
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    Switch

    All this for a switch. I'll wager that there is an exact same switch available from several other sources at a fraction of the cost of the switch from BMW. Just takes a bit of research. It may even be made by the same manufacturer that supplies the part for BMW.
    Moving the master cylinder to the handlebar is definitely an improvement. If you want to keep the part under the tank then I've found that sleeving the bore with stainless steel is the best way to make it work. Most master cylinder bores that I've seen end up to be too pitted to accept a simple hone and boreing them out will go beyond the limits of the stock piston and seals or the pistons ans seals in the rebuild kit.
    Finally, I guess that when BMW says to flush/replace the brake fluid at least once a year, they may know what they're talking about. I've lost track of how many rust pitted master cylinder bores and caliper pistons I've seen due to a lack of this simple maintenance step.
    Boxerbruce

  8. #8
    Airmarshal-IL James.A's Avatar
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    I have to wonder which brake switch we are talking about. On many models the switch that turns on the rear brake light is actuated by the right front bake lever. The switch that lights the brake when you mash the rear brake lever is always a sort of limit switch that is actuated by mechanicly by the rear brake. On some models the light that shows a brake failure is part of a float switch on the cap of the under-tank front brake master cylinder. Some models have a pressure switch on the front of the master cylinder. What exactly are we talking about here. Every airhead I've owned that had a handle bar master cylinder had a switch on the right side hand set that lit the brake light when the rider grabbed the front brake lever. My pre '75 airheads also had a brake light switch on the right side hand set.

    So many variables.... In my recollection, on a 1978 /7 , the right front brake lever has a small switch that is actuated by the front hand brake lever. Look for small wires leading to the right hand brake lever.
    1973 R75/5

  9. #9
    Rally Rat 1074's Avatar
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    Switch

    If it's an original 1978 bike then the switch is mounted on the front of the master cylinder that is under the tank. The brake failure switch and assigned warning light can be found on all bikes that came with the master cylinder under the tank. My guess is that they figured that the rider couldn't see the fluid level in the under the tank model therefore the need for that light. Once the master cylinder was moved to the handlebar then it would be assumed that the rider could just look at it and tell if it needed topping off.
    With the master cylinder on the handlebar they could and did, mount the switch in varying locations. The most distinct hydraulic actuated switch as I recall was behind the headlight on the R65 models. Again, as I remember, most models had an electric contact switch on the right control assembly.
    Boxerbruce

  10. #10
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    Brake Switch

    Quote Originally Posted by James.A View Post
    I have to wonder which brake switch we are talking about. On many models the switch that turns on the rear brake light is actuated by the right front bake lever. The switch that lights the brake when you mash the rear brake lever is always a sort of limit switch that is actuated by mechanicly by the rear brake. On some models the light that shows a brake failure is part of a float switch on the cap of the under-tank front brake master cylinder. Some models have a pressure switch on the front of the master cylinder. What exactly are we talking about here. Every airhead I've owned that had a handle bar master cylinder had a switch on the right side hand set that lit the brake light when the rider grabbed the front brake lever. My pre '75 airheads also had a brake light switch on the right side hand set.

    So many variables.... In my recollection, on a 1978 /7 , the right front brake lever has a small switch that is actuated by the front hand brake lever. Look for small wires leading to the right hand brake lever.
    Jim you can look at my 1978 R100/7 on Saturday at the tech day, bike has the under tank master cylinder don't know where the switch is
    P.S. Before I put the tank on I looked at my brake fluid, I will be bringing the mighty vac and some brake fluid what is there looks bad

  11. #11
    The standard /7 had the front switch on the M/C under the tank. Had the rear brake light switch connected to the rear brake arm just under the swingarm. Both activated the rear brake light.
    "The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers

  12. #12
    Registered User toooldtocare's Avatar
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    Quote Originally Posted by James.A View Post
    I have to wonder which brake switch we are talking about. On many models the switch that turns on the rear brake light is actuated by the right front bake lever. The switch that lights the brake when you mash the rear brake lever is always a sort of limit switch that is actuated by mechanicly by the rear brake. On some models the light that shows a brake failure is part of a float switch on the cap of the under-tank front brake master cylinder. Some models have a pressure switch on the front of the master cylinder. What exactly are we talking about here. Every airhead I've owned that had a handle bar master cylinder had a switch on the right side hand set that lit the brake light when the rider grabbed the front brake lever. My pre '75 airheads also had a brake light switch on the right side hand set.

    So many variables.... In my recollection, on a 1978 /7 , the right front brake lever has a small switch that is actuated by the front hand brake lever. Look for small wires leading to the right hand brake lever.
    Picture taken from the internet, 1977 R100RS under tank master cylinder. This configuration is the same as my 1978 R100RS. Note the two prongs in the left photo, that is the connector to the pressure switch (silver part in front of the master cylinder) that turns on the brake light. The photo on the right shows the master cylinder mounted on the bike. Note the wires from the master cylinder cap in the photo on the right, that is the level float that turns on the brake failure light on the dash.

    Hope this helps,

    Wayne
    Attached Images Attached Images

  13. #13
    The main difference between the RS and the standard /7 is the fact that the RS had twin front disk brakes, whereas the /7 only had one. Therefore, the master cylinder on the RS had two tapped holes for the two brake lines out, one to each side of the front wheel. I also believe that the bores were different as the /7 only had to move enough fluid for one brake, but the RS had to move enough fluid for two brakes.
    "The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers

  14. #14
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    Quote Originally Posted by SCBuckeye View Post
    If I were you, I would bite the bullet NOW and upgrade to the handlebar master cylinder and brake switch. I tried to do use and rebuild my M/C after spending around $70 for a rebuild kit. Lasted about 2-1/2 years and started leaking again - getting on all those relays and switches under the tank. The handlebar upgrade changed everything for the better!

    Just sayin......
    +1
    Dave Hutton '78 R100S (mfg 7/77)

  15. #15
    I tried a 10 dollar switch for a hd and the threads were similar but not right. I ended up paying for the capital cycle switch that fit right. The MC was working fine it was just the switch that was sticking.

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