My rear brakeswitch gave up the ghost and I quickly discovered that it wasn't going to come out of the mounting bracket because it was corroded solid in there. What appears to be a solid hex is a metal stamping and it collapses quite easily. As I was making a set of braided lines to fit LFB anyway, my solution was to fit a hydraulic switch instead.



The wires obviously aren't going to reach the sidepanel, so I extended them with 16/0.2 thinwall by soldering the ends together and sheathing with heatshrink. I then covered the lot with PVC sleeving. At the other end I cut off the existing plug and crimped on female Japanese connectors.



The only change on the brake line from standard at the caliper end was to use a banjo bolt.



I bought a batch of hydraulic switches from China via ebay: £15.00 for six switches as opposed to £11.50 for one switch here. They're exactly the same item.

Thanks for the warning. My rear brake switch is kaput too and not done because the old one doesn't want to come out. I haven't applied brute force as that never seems to work on these things. Space to get at it is tight.

Your rear brake fluid reservoir seems to have an interesting mounting.....stainless steel?

I have never been keen on pressure operated brake switches because you can't just tap the lever to bring the light on for a moment without working the brake.

92KK K100LT 193214 wrote:
Your rear brake fluid reservoir seems to have an interesting mounting.....stainless steel?

Yes - this is actually MkII because as you can see, I had to replace the hydraulic reservoir too - a friend made this one for me many years ago but for a different bike. I'm sure Fritz had just returned from Oktoberfest when he designed the original bracket - having to remove the battery just to remove the footrest hanger? MkI was a simple right-angle that held the BMW reservoir and slid down behind the footrest hanger in place of the standard penny washer.

RicK G wrote:I have never been keen on pressure operated brake switches because you can't just tap the lever to bring the light on for a moment without working the brake.

There is that. It's a tradeoff between long term reliability and being able to tell the guy behind you to back off.

Sorry to ressurect an old thread.  Would a hydraulic switch work on the front brake in place of the manual switch? 

I ask because the front brake switch works by releasing the switch button (and I don't know what's actually going on inside that switch).  I don't know if that's differnet than the mechanism by which a hydraulic switch works (or if it even matters). 

BTW, I put a hydraulic switch on my rear brake and it works great.  But I did it long enough ago that I don't recall how the OEM switch worked (if I ever knew) and whether it differs from the front.

KJustin,

Depends on which K100 you have. Mine is 84 and the front and rear brake switch and also the clutch lever brake switch are the same parts! When you pull the lever the little plastic plunger [should] come out and [should] complete a circuit inside the switch to illuminate the brake light, or allow the starter to operate.

Olaf, thank you.  What you describe is what I have on my 85 K100RT (now cafe'd) and perfectly answers the queston.  Therefore, a hydraulic switch should work fine on the front brake. It will be a few weeks until I make this mod as I'm in the middle of some other things right now.  I'll report back to the forum if there's any problem.  If you don't hear from me, all future readers of this thread can assume it worked fine.

It will be fine - I have hydraulic switches on LFB, so you have nothing to worry about.

KJustin wrote:Olaf, thank you.  What you describe is what I have on my 85 K100RT (now cafe'd) and perfectly answers the queston.  Therefore, a hydraulic switch should work fine on the front brake. It will be a few weeks until I make this mod as I'm in the middle of some other things right now.  I'll report back to the forum if there's any problem.  If you don't hear from me, all future readers of this thread can assume it worked fine.

Thanks for that. What you describe will work but I also subscribe to being able to flash the brakes without using them. The hydraulic switch only works AFTER you have started to pressurise the brake circuit. The switch works by exposing the pin within the range of the free play at the lever, ie before you pressurise the brakes. I ride the K all year including frost and its quite useful when you are braking very very slowly to have a brake light on. The other thing is and its pedantic is that the three switches being same you can swap them around quite easily if you do get a failure. However you can always develop the habit of tapping one or other brake first if one of them has a switch but my preference particularly on the rear is to have the ability to flash or use a brake light. Enough of having following vehicles a little too close for comfort!

Funny thing too any car I have had has a switch and not a pressure sensor, located at the foot brake pedal.