1. Organic disc
Organic friction material is made of cellulose, usually reinforced with
some heat resistant stuff like chopped fiberglass and mineral wool in a
thermosetting phenolic resin base.
The cellulose is like cardboard and helps initial grip.
The mineral wool and fiberglass strands provide burst strength, which is
the friction material’s resistance to breaking up and falling
apart, especially with shear and centrifugal load.
2. Heavy duty
Heavy Duty (HD) and racing discs have friction material made of several different
A mild HD disc usually uses chopped Kevlar strands in a phenolic resin base. Kevlar
is a space-age aramid fiber that is six times stronger than steel in tension and is
fairly heat resistant.
Kevlar offers good burst strength and good wearing characteristics but has
relatively poor frictional gripping properties. This makes for smooth engagement
characteristics but only average grip.
• usually the best compromise for modified streetcar because they have a
nice balance between smoothness, long life, good grip and low wear.
• typical semi-metallic is an organic disc with strands of copper or brass
woven through it. The metal strands help improve burst strength and allow
for more consistent grip under higher temperatures. The metal helps
dissipate heat through the material as well.
• More aggressive semi-metallics designed for heavier abuse have powdered
ceramics, copper, bronze, carbon or iron added to the organic based
mixture to help improve grip at higher temperatures.
For extreme applications because use a sintered copper or bronze (or a mixture of
both) friction material that usually contains particles of ceramic and perhaps iron or
It is made by compressing the mixture of powdered copper, bronze, iron, carbon
and ceramics at high heat and pressure. Copper and bronze are excellent conductors
of heat and have self-lubricating properties The iron, carbon and ceramics are friction
modifiers that help give the copper bite.
These materials are very resistant to heat and abuse, and actually bite harder with
more heat but they can still be overheated in extreme cases and the copper can
smear and melt over the friction modifier particles ruining the disc.
5. Carbon - carbon
The latest in disc friction material technology and refers to all of the friction surfaces
of the clutch from the disc or discs, the pressure ring and the flywheel surface.
made from amorphous carbon (solid carbon).
It is strong and very burst resistant, very light, very smooth and it has excellent grip
that gets better at higher temperatures.
It lasts the longest of any friction material and it is non-abrasive.
Carbon only has two drawbacks, one is its very expensive, and two it tends to wear
faster at lower temperatures.
A slightly cheaper alternative is carbon-steel.
Diaphragm Style pressure plate assemblies produce
clamp load with pressure from a “Belleville spring”,
commonly referred to as a diaphragm spring.
Created from heat-treated spring steel, the diaphragm
spring is stamped into an oval one-piece concave shape
with slits that separate the spring fingers.
In addition to the diaphragm spring, typical diaphragm
assemblies are comprised of a pressure plate, pivot ring,
drive straps, rivets, and a cover stamping.
• diaphragm assemblies actually increase the clamping force during the
first half of service life before returning to the original clamp load.
• Diaphragm assemblies also require less pedal effort to disengage the
system, and they contain fewer moving parts.
• pressure is applied against the tips of the diaphragm spring and they
are pushed toward the flywheel. The opposite end (outside
diameter) of the diaphragm pivots on a pivot ring away from the
• The pressure plate is then pulled away from the flywheel by the use
of diaphragm straps that connect the pressure plate to the cover
• Clutch release bearings are a type of thrust bearings which are
sometimes referred to as clutch throw out bearings.
• Their main function is to release the clutch while reducing friction
between the pressure plate levers and the release fingers.
• These bearings constitute a ball bearing and a collar assembly and
they may either be controlled mechanically of hydraulically.
Clutch release fork
• The clutch fork, also called a clutch arm or release arm, transfers
motion from the release mechanism to the release bearing and
• 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
I. Linkage type
• consists of a bellcrank that pivots between the frame and the engine
block. One side of the bell crank attaches to the clutch pedal, and the
opposite side attaches to the adjustment rod for clutch release.
• The adjustment rod is inserted into the clutch fork and lengthened or
shortened to achieve the proper release and gap between the clutch
fingers and the bearing.
• the ratio between the release mechanism and the pedal effort is between
three and four to one. Mechanical linkages provide the most flexibility in
II. Cable type clutch
• A cable linkage can perform the same controlling action as the mechanical clutch
but with fewer parts.
• The clutch cable system does not take up much room.
• It also has the advantage of flexible installation so it can be routed around the
power brake and steering units.
• These advantages help to make it the most commonly used clutch linkage.
III. Hydraulic type clutch
• In the hydraulic clutch linkage system, hydraulic pressure transmits
motion from one sealed cylinder to another through a hydraulic line.
• Like the cable linkage assembly, the hydraulic linkage is compact
• Hydraulic linkages allow the placement of the release fork anywhere
that gives which gives more flexibility in body design