rear brake cable gts

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bobnorton
860 GT / GTS
Posts: 280
Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

rear brake cable gts

Post by bobnorton » Tue May 28, 2013 2:26 am

for some reason my rear brake light is always on. I've had it to bits and the switch seems to be working fine and no amount of fidling with adjustment helps. I'm wondering if the outer sheath is too long and applying pressure which is operating the switch. Is there a specified length?

machten
MHR / S2
Posts: 481
Joined: Sun Oct 29, 2006 8:37 am
Location: Perth, Western Australia

Re: rear brake cable gts

Post by machten » Tue May 28, 2013 4:50 am

Bob,

I'm assuming the 900 GTS has the same rear hub assembly and in line switch arrangement as the 860 GT, 750 GT and 750 Sport.

If so, those switches are a right PITA. The first thing to check is that your brake shoes aren't too worn. If they are, then the adjusted position could be taking too much pre-load from the brake shoe springs and the tension is enough to close the switch.

What seems to happen is that when you adjust your brake cable length to satisfy your brakes coming on at the right pedal position (this is effectively adjusting the resting distance between the shoes and the drum friction surface - and as your shoes wear to have to rachet up against the shoes spring tension), the brake shoe springs provide enough pressure to close the circuit in the switch.

That being said, I've problems with those cable switches with new radiused shoes in place. If you've taken one of those switches apart, you'll see that is simply a slice of rubber that is seperating the contact surfaces. Different cables I've had have had rubbers with varying compression characteristics. The pressure compresses the rubber enough and the circuit is closed.

Often also, the cable routing contributes to the problem. In particular, the cable needs to trail as perpendicular as possible to the switch, as pulling the tension on an angle then only has to compress one side of the rubber to close the circuit.

I got heartily sick of those switches doing the same thing to me and rigged up a "rider's bodge" on my 750 Sport and 750 GT pictured below. Won't pass a concours, but it works admirablely and has been in place for about 5,000km so far. Basically it is a loop of flexible 100lb stainless steel fishing trace braid that holds the latent brake shoe spring tension at rest so that switch doesn't bear the weight. I've seen a neater arrangement that does the same thing with a neat fixed wire arrangement that looks like it was made for the job, but I haven't got arround to that yet. Maybe in another 5,000km. :roll:

Not recommending it...just saying it's what I've done.

Image

Kev

bobnorton
860 GT / GTS
Posts: 280
Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

Re: rear brake cable gts

Post by bobnorton » Tue May 28, 2013 6:17 am

Thanks mate, i'll do something similar.

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