(click on any image to enlarge)
plate applies pressure to the clutch disc to clamp
it against the flywheel and engage the clutch.
Pressure may be generated by spring (static) pressure or centrifugal pressure.
Static pressure is constant, meaning that whether the engine is turned
off or spinning 7000 RPM, the pressure never changes.
Centrifugal pressure is not constant. It is a function of engine
RPM. Centrifugal pressure is
generated by the clutch levers and increases to the square of the engine RPM.
It is less pronounced at lower engine speeds but very effective in the
higher RPM range.
diaphragm pressure plate
pressure plate utilizes a Bellville or conical spring to apply pressure to the
pressure ring. This type of
pressure plate has multiple fingers that
the release bearing presses against to disengage the clutch.
Diaphragm clutches rely completely on static pressure which is unaffected by
spring allows the pressure plate to be released and engaged with a relatively
light pedal effort compared with coil spring clutches.
This design is used almost exclusively in late model vehicles that have
hydraulic or cable release mechanisms, due to the lighter effort required to
engage and disengage the pressure plate.
clutch is excellent for use in street and heavy duty street applications where
drivability and pedal effort are a major concern for the user.
TIP – CENTRIFUGAL WEIGHTS IN DIAPHRAGM STREET/STRIP APPLICATIONS
aftermarket diaphragm pressure plates feature a centrifugal weighting
system. Centrifugal assist is useful in drag racing and
other high RPM applications to apply additional clamp load to the clutch
disc. The drawback to
centrifugal assist in highway performance applications is that the
centrifugal assist is low until the engine reaches high RPM. The
load on the clutch (the effort required to turn the driveshaft) is very
high at low RPM and decreases at higher RPM.
In most highway applications centrifugal assist is not effective
in increasing holding power or performance because it fails to solve the
high torque load at low RPM problem.
BECK PRESSURE PLATES
& Beck pressure plate
The Borg &
Beck pressure plate uses three levers to engage and disengage the clutch disc.
It is a coil spring design, where the pressure of the clutch is applied
to the disc using coil springs similar to a valve spring.
By combining these springs at a specific installed height, different
pressures can be attained for the pressure plate. Borg
& Beck clutches rely completely on static pressure which is unaffected by
Beck pressure plates are found in GM, Chrysler, and AMC early model applications
with mechanical linkage. Borg & Beck
clutches and can be identified by looking at the width of the clutch
fingers, which is about one inch. The
coil spring design by nature will require more pedal effort to engage and
disengage the clutch.
Borg and Beck
clutches are best suited to street and heavy duty street applications for older
muscle cars and trucks.
lever (top) and standard lever (bottom).
Style pressure plate
added to the clutch levers to increase the plate pressure as RPM
pressure plates are the Ford version of a three lever, coil spring pressure
plate. The Long Style is the most
popular type of pressure plate for drag racing applications. It's design
is the basis for today’s professional drag racing clutches.
advantage of Long Style pressure plates is their ability to apply centrifugal
clamping pressure. As engine RPM increases, the
levers in the plate pivot against the cover and apply additional clamp load to
the clutch disc. This is true in
both counterweighted lever Long Style pressure plates and also
non-counterweighted designs. (Counterweighted
levers have provision for installation of weights to the backside of the levers
to further increase the centrifugal clamp effect.)
The The Long
Style pressure plate is best utilized with mechanical release linkages.
Long Style clutches were prevalent in early Ford muscle cars and trucks.
Style clutches feature adjustable static pressure. By turning an allen
screw located on top of the spring, the pressure can be increased.
TIP - ADJUSTING STATIC PRESSURE ON RAM LONG STYLE CLUTCHES
Increasing the static
pressure of a RAM Long Style pressure plate is achieved by turning the
allen adjuster screw COUNTERCLOCKWISE to increase the static load.
When the screw is turned, it pushed against the cover and the adjuster
base compresses the spring, increasing the spring rate. Most
pressure plates have a maximum of 7 turns adjustment. Turning the
adjuster screw further will cause it to come out of the adjuster base.
When this occurs, the entire plate must be disassembled for repair.
Some racers mark the turns they have in the clutch on the side of the
bellhousing in order to keep track of where they are set.
As the adjuster screw is
turned counterclockwise, the spring is compressed to increase clamp
TECH TIP –
CENTRIFUGAL OR COUNTERWEIGHT LOADING
pressure is additional clamping pressure on the clutch disc that occurs
as a function of engine RPM. As
engine RPM increases, centrifugal pressure forces the clutch fingers of
the Long Style pressure plate outward.
As this occurs, the clutch fingers pivot against the cover and
apply additional clamp loading to the clutch disc.