About 2 months ago I replaced the brake pads on my TR250. The old ones were
almost compeltely worn so I had to push the pistons back into the caliper
body to make room for the new pads. About 30 miles later, while driving
up a large hill, I pushed down on the brake pedal and almost nothing
happened. I took this opportunity to rebuild the brakes, among other
parts, and found out what had caused the failure. The pistons had rusted
and pitted up to, but not past, the sealing gasket in between the caliper
body and the piston. When I pushed the pistons back into the body the
seal was now resting on the pitted area of the piston which didn't make
a good oil seal, and the brake fluid squirted out through the rust.
I guess the piston boot can be expected to keep out only *almost* all
of the moisture.
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