Hydraulic Release System

Power transfer between pedal and clutch

Vehicles with foot-pedal operated single disc dry clutches require a mechanism to transfer the power between the pedal and the clutch.

Originally, pedal forces were transmitted via a cable to a lever in the clutch bell housing. As engine compartments grew ever smaller it became increasingly difficult to fit a cable in a straight line between the pedal and the lever.

Modern clutch systems therefore use a hydraulic release system.

Semi-hydraulic

In the so-called semi-hydraulic system the cable is replaced by a hydraulic line comprising a master cylinder on the pedal, a line and a slave cylinder on the outside of the transmission.

Release system with central release

A release system with a central release has no lever in the transmission bell housing. A hydraulic cylinder with an integrated release bearing replaces the conventional release bearing.

This is located centrally with respect to the clutch disc hub and to the diaphragm spring inside the clutch bell housing. Fully hydraulic systems have the advantage of being easy to fit as they have few parts. There are also far more options for fitting the hydraulic cable inside the engine compartment.