The function of a slave cylinder is primarily controlled by the master cylinder. Slave cylinders are divided into two primary categories: Concentric slave cylinder (CSC) and external slave cylinder.

The CSC is mounted inside the bell housing where the release bearing retainer is normally attached. This unique design offers the following benefits: Elimination of the clutch fork and related hardware, precise release bearing travel with better alignment geometry, and closer fit to the transmission which increases flexibility in passenger compartment design.

A CSC uses a large coil spring to maintain constant contact between the bearing face and diaphragm spring fingers. Therefore, no “lost travel” is required between the bearing and diaphragm spring before the pressure plate begins to disengage.
 

As the name implies, external slave cylinders are normally mounted on the outside of the transmission bell housing. They consist of few moving parts other than a piston, internal spring, and pushrod. A rubber boot is usually used to seal contaminants away from the moving parts. The release bearing used in this system always maintains preloaded contact with the diaphragm spring.
 

The external end of the pushrod is normally tipped with a plastic, mushroom-shaped, bushing that serves to reduce noise and eliminate surface wear on the clutch fork pushrod tip. The plastic bushing is also important because it helps determine the overall length of the rod. This exact length is very critical in the overall function of the hydraulic system.