If the piston cups are swollen, the rubber parts have deteriorated. This deterioration may also be identified by observing swollen master cylinder cover diaphragms.

If rubber deterioration is evident, disassemble all hydraulic parts and wash with alcohol. Dry parts with dry unlubricated compressed air before assembly to keep alcohol out of the system. Replace all rubber parts in the system, including hoses. Check for fluid on the brake pads. If excessive fluid is found, replace the brake pads.

If master cylinder piston seals are satisfactory, check for leakage or excessive heat conditions. If conditions are not found, drain fluid, flush with brake fluid, fill and bleed the system.