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R1100RT Brake Problem


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Changed the front pads yesterday. In doing so, the pistons on the left caliper wouldn't retract to allow fitting the new thicker pads. Push one in and another would push out. The right acted normally.


Got it done by opening the bleeder on the left caliper. Took a test ride and the brakes weren't very strong. Squeezed the lever repeatedly and the left brake hose blew. I will change out the brake hose, considering changing them all to Spiegler stainless lines.


The remaining question is what was preventing the left caliper brake fluid from returning to the reservoir?

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Afternoon migrant


A couple of possibilities,


One is the take-up port hole in the master cylinder is plugged. This is possible but unlikely if the Right caliper retracted OK.


The other possibility is the brake hose had separated inside and the inner liner was blocking the fluid return (it doesn’t happen often but can happen)


Unless you pushed both pistons back at the same time there is no way of knowing for sure if there was a valid return blockage or just one piston being pushed in pushed the other piston out.


In any case you have a bad brake hose so replace that then see where you are at.


Added: when you remove the old brake hose try blowing back through it to see if it is restricted inside.

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Evening migrant




You know there is another possibility. If the pad replacement on the R/H side pushed enough fluid back into the master cylinder reservoir to fill it there would have been no place for the fluid to go when you did the left (is the reservoir completely full now?)


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Thanks for the response. The left side was done first. After unable to push in pistons separately, I put both new pads in and tried a screwdriver between the pads prying lightly. No movement.


When I stopped at the turnaround point of my test ride, I felt both discs...left one cold, right warm. Seems like something was blocking the fluid within the hose. That's when I pumped the lever and the hose blew.

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Clean the pistons, then, use a C-clamp against the OLD pad to push both pistons in simultaneously. As dirtrider observed, pay close attention reservoir levels as you push the pistons back in.

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