Lost rear brakes!!

[jenunn]

I took a short ride yesterday and while pulling into a gas station noticed a little drag on what I thought was the front brake as I pulled up to the pump. After filling up, I did a visual inspection and saw nothing amiss. Rolled the bike a little forwards and backwards and wheels were turning freely so I headed home. The first time I went to use the brakes, the rear brake pedal felt soft and spongy. Several stops later, the rear brake pedal would "bottom out" and did not provide any braking. When home I noticed the rear master cylinder was totally empty, though I have never seen any evidence of a leak. Any idea of the first place I should look? I am guessing there may be a leak in one of the caliper seals.

Jim N.
2002 1150GS
ABS II (Brembo)

:confused:

[TheRoss]

Any signs of leaking fluid?

I would check your brake pads and replace if needed. Then refill the brake fluid, bleed the system well, and ride the bike. See if normal operation comes back. It is possible that you have just worn your brake pads down to nothing, which could explain the loss of fluid in the resevior. Especially if the fluid level was low when the pads were new.

I am a big fan of SpeedBleeders. With your Brembo calipers you can easily do the work yourself.

If the pistons in the caliper are sticking, they would likely lock onto the disc and then not let go, not slide back into the caliper when the brake lever is released. But this would not cause fluid to escape. And you said there is not big time drag on the wheels. The time this happened on my RT the wheel was locked.

[jenunn]

TheRoss - I appreciate your insight. This is probably what happened, though I have not yet pulled the calipers to verify. Did you use OEM pads on your RT or after market pads?

[TheRoss]

I use EBC pads on the rear and DP pads on the front. The DP pads are a little more expensive than the EBCs but they have the metal clip which keeps them from rattling. Both are cheaper than the BMW branded pads.

I think you just got air in the brake line. Which could happen if the fluid runs too low.

[rmeisen]

Doesn't ABS II have two separate fluid sections, one on the top side from the pedal/master cylinder to the ABS Unit and a separate one on the bottom side from the ABS Unit to the Caliper. The two are not connected. If the upper section is going dry, it probably would not be because of the pads..

[TheRoss]

My RT has ABS2 and only 1 reservior for the rear, and 1 reservoir for the front. Maybe the GS model is different?

My K1200RS, which did not have linked brakes, and had Brembo calipers, only had 1 rear reservoir. But my buddy's RS, which is 2 years newer and has linked brakes, and BMW calipers, has 2 rear reservoirs just as you're suggesting.