I have been on 2 group rides recently and on both, I was told my rear brake light was briefly coming on when clearly I wouldn’t be braking. I took a long hard look at the rear brake lever set up and the brake light microswitch doesn't need much movement of the lever to operate and I also notice the rear brake lever return spring isn’t particularly stiff. Pretty confident my boot isn’t snagging the lever which leaves me with the concept, that on uneven road surfaces, the weight of the rear brake lever is sufficient to overcome the return spring and move enough for the microswitch to operate. Any suggestions ? Andy
Sure your foot isn't resting on the lever? Had a mate with a GS who's light was doing the same, his toe was just resting on the tip of the lever, just enough to operate the brake light but not enough to operate the brake, bit of adjustment sorted it.
Yes, absolutely sure, despite my size 47 Daytonas Unlike my Mutlistrada 1200, I’m definitely ball of the foot on the foot peg on the Pikes Peak. Andy
It’s an off the shelf microswitch which looks very similar to the switch on the front brake. The way the switch is mounted to the footrest bracket, gives no adjustment to when it operates. The bolt #17 just adjusts the height of the brake lever, keeping the distance the top of the bolt has to travel to operate the switch, constant. I think I might change the return spring #18 in the hope it will be stiffer. Andy
Also - just checking - the microswitch .. is it the same as on my BMW - it's closed normally and the act of braking opens the switch to turn on the brake light. So it would be less susceptible to small movements that might bump it open ?
Not familiar with the BMW but yes, normally closed (open circuit) and movement of the brake lever makes the circuit (voltage). However, the brake lever (at the switch), only has to make a very small movement, maybe no more than 2mm for the switch to operate. I've ordered a new return spring, it's only a fiver. Andy
Put an extra spring on the rear lever to be sure that it isn’t bouncing like you said. An elastic band or two might do the trick temporarily whilst your trusty follower verifies whether or not it solves the problem.
Disconnect the switch before next ride and see if you get any reports from your group. If no, likely the rear brake switch rather than front.
Could be wrong, but I think bolt doesn’t affect the position of the pedal, not to any great extent anyway. Its height however, does change the point at which the microswitch activates. Mine needed adjusting when I changed the pedal to a Ducabike version. It’s worth checking how easily the light activates by applying some pressure to the pedal. It’s pretty easy to adjust, just undo the locknut (14) and reposition.
I had this problem on my 1260 and ended up bending the spring steel arm on the microswitch to cure it. BUT my V4S is different, the microswitch doesn't seem to operate the brake light, I am pretty sure there is a pressure switch in the braking system somewhere that activates the brake light. I believe on the V4S that the microswitch is there to deactivate the ACC and the same applies to the front brake. Of course I could be wrong ! What I do know is when using ACC (eg on a motorway) and the bike needs to slow down it will apply the brakes as needed and if it does need to brake then the brake light comes on! I have tried this out with a mate (on comms) following me and he confirmed the brake light comes on and I had not touched either of the brake levers. No idea where the pressure switch is, these bikes are getting too clever
Part#4 on the diagram I posted, is described as “switch, rear brake” and if remove the switch from its bracket, manual operation of the switch, turns the brake light on/off. I see your point about the adaptive cruise though, fortunately, it’s a function I don’t use Andy
I'll complicate this a bit more Bike switched on but not started. If I hold the rear brake microswitch up with a thin screwdriver, so it does not activate, the rear brake lever will move down easily initially with no brake light on, then with more pressure on the lever the brake light will come on! I have had a discussion with my dealer about this as it happens and they don't know how it works either .
