'08 GS Adv: No rear brake after service
I just did my ~24,000 service on my 2008 R1200GS Adventure with just under 60,000 miles on it, a task I've done several times before on this and previous 1200GS bikes.
As part of that service I did a brake fluid flush, a task I've done before (also have done brake pad replacement before) on this bike, no previous problems. As usual, I wiggled the rear caliper a little before removal from rotor to slightly spread pads to ease re-installation afterwards.
This time, however, while front brakes bled fine and are working AOK, rear brakes are non-functional. Have pumped the pedal maybe 100 times in a row and can't get anything like pressure in the rear brake system with bleed valve closed. With bleed valve open have no fluid coming out of valve, and fluid level in rear reservoir remains unchanged. Pedal pumps up and down and apparently does nothing.
Thinking the rear brake master cylinder is bad, but before I order a $217 part I thought I'd pass the problem by the collective wisdom found here. :-)
Could the problem perhaps be air trapped in the rear caliper? I didn't fully depress the pistons when I took the caliper off the rotor, just wiggled the pads a bit loose to ease re-installation afterwards. Still, even if air is trapped in rear caliper, wouldn't brake fluid still come out of the bleed valve, and leave the reservoir, when bleeding (but the trapped air in caliper would leave pedal soft)?
If it does come to replacing the rear brake master cylinder, anything special I should be aware of? Do I just unbolt the old one, bolt in a new one, and run a bunch of DOT4 through the system, normal bleeding style? (I do have the GS-911 for doing the ABS bleed function.)
I should also mention that I've almost never touched the rear brake in nearly 60,000 miles, using it only very rarely, but I did use it a few times in the last month and it was working OK at that point. Also, I don't see any fluid leaking from anywhere, not rear caliper, not master cylinder, not reservoir.