A hydraulic clutch release mechanism (fig. 4-5)
uses a simple hydraulic circuit to transfer clutch pedal
action to the clutch fork. It has three basic
partsmaster cylinder, hydraulic lines, and a slave
Movement of the clutch pedal creates hydraulic
pressure in the master cylinder, which actuates the
slave cylinder. The slave cylinder then moves the
The clutch fork, also called a clutch arm or release
arm, transfers motion from the release mechanism to
the release bearing and pressure plate. The clutch fork
sticks through a square hole in the bell housing and
mounts on a pivot. When the clutch fork is moved by
the release mechanism, it PRIES on the release bearing
to disengage the clutch.
A rubber boot fits over the clutch fork. This boot is
designed to keep road dirt, rocks, oil, water, and other
debris from entering the clutch housing.
assembly, with the manual transmission bolted to the
back of the housing. The lower front of the housing has
a metal cover that can be removed for fly-wheel ring
gear inspection or when the engine must be separated
from the clutch assembly. A hole is provided in the side
of the housing for the clutch fork. It can be made of
aluminum, magnesium, or cast iron.
The release bearing, also called the throw-out
bearing, is a ball bearing and collar assembly. It
reduces friction between the pressure plate levers and
the release fork. The release bearing is a sealed unit
pack with a lubricant. It slides on a hub sleeve
extending out from the front of the manual
transmission or transaxle.
The release bearing snaps over the end of the
clutch fork. Small spring clips hold the bearing on the
fork. Then fork movement in either direction slides the
release bearing along the transmission hub sleeve.
The clutch housing is also called the bell housing.
It bolts to the rear of the engine, enclosing the clutch
The pressure plate is a spring-loaded device that
can either engage or disengage the clutch disc and the
flywheel. It bolts to the flywheel. The clutch disc fits
Figure 4-5.Hydraulic clutch release mechanism.