Intermittant front brake binding.. and one cause and solution..

[rocks]

A GSA that came with us on the Adventure rider rally last weekend hit a bit of trouble.
(Ride report here: http://www.ukgser.com/forums/showthread.php?t=104463

In the afternoon on saturday the GSA was taken for a bit of a "detour" and got dropped.. shortly afterward it started to suffer from front brake binding.

The brake calliper was cleared of crap, mud grass etc and this seemed to solve it however a few miles further on and it was binding again an getting very hot. The master cylinder was openned and pressure blead out this seemed to resolve it.

No warning lights etc were reportedly coming on.. however the cuase of it was not actually any fault. Just the right hand, hand guard having been knocked down during the fall ever so slightly, just enough to stop the brake lever extending far enough forward. This cause a minor increase in front brake pressure which eventually created enough heat for the brake to start to bind more aggressively so it would appear. Each time followng a stop the fluid would cool and problem go away for a few miles..lol.

Just though as it so easily happened that you guys might wish to know. Fix was to return hand gard to original position so not restricting the lever travel.

 

[John Armstrong]

Was there any of the "brake failure" warnings or other warnings that the brakes weren't "perfect"?

 

[rocks]

No warning lights at all..

Nope, by account there were NO warning lights. The ABS enabled as per usualy when on the road sections etc/turn off on off-road.

Apparently there was some debate that the system should detect if a brake lever is depressed whilst it does it diagnostic works on start up, but this didnt seem to be the case. May the lever was not depressed far enough, just enough to create a fraction more pressure on the pads/discs to generate the heat.

The bike was fine on sunday and even made it over strata florida

 

[John Armstrong]

Thanks, may be if the brake lever isn't on enough to make the micro switch, it'll pass the bite test and still work normally. Guess the lesson is if you drop a 1200 then check both front and rear brakes fully.

 

[rocks]

Nope.. check the hand guards..

Yes thats what I figured in the end.. there is enough movement in the lever before any switches/sensors are triggered.

The brakes function was checked several times till someone spotted the hand guard and marks the lever had left on the inside of it. We failed to spot untill then was the position of the hand guard fouling the lever.

So if you drop a 1200, then check the hand guard is not restricting the leavers after you have picked it up. Especially the right hand one.

 

[(RIP) Kaister]

all master cylinders have a return path via a small drilling. This bleeds off excess pressure and fluid expansion .

if you block this hole by having the piston in the wrong place - via the handguard or wrong adjustment - then you'll get pressure build up exactly as you describe.

exactly the same for the rear.

always check for 1 or 2 mm play at the lever 'push' point - front or back