Master Cylinder Diagnostics

Although the mechanics of modern master cylinders seem deceptively simple, today’s dual-piston or tandem master cylinders still require the utmost in care and attention to maintain safe, reliable operation.    The most important point to remember during any master cylinder diagnosis is that an inch of travel at the brake pedal translates into only a few thousandths of an inch of piston travel at a disc brake caliper or brake cylinder. Consequently, the fluid displacement of a master cylinder is matched very closely to the fluid volume requirements of the brake system itself. Obviously, the clearance between a brake pad and rotor may drastically affect master cylinder operation. Some caliper applications use a square-cut piston seal to retract the piston a few thousandths of an inch when the brakes are released. Some caliper applications may require a “quick-take-up” cylinder to close these relatively large pad-to-rotor clearances as the brake pedal is applied.