Slave cylinder

A slave cylinder is the part of a hydraulic system that does the work at the far end. When you pull the lever, the master cylinder pushes fluid through a hose, and the slave cylinder's piston moves to release the clutch. On a motorcycle the term is used mostly for hydraulic clutches; in hydraulic brakes the equivalent pistons sit in the brake caliper.

Symptoms of a failing clutch slave cylinder are a spongy or sinking lever, a clutch that does not fully disengage (dragging, hard to find neutral) and fluid leaks near the engine cover.

Change the fluid as specified (usually DOT 4 or mineral oil, depending on the system; never mix them), and bleed air out after any work. Seal kits are available for many slave cylinders.