Lever Style
Lever style pressure plate assemblies produce clamp load with pressure from coil springs, located inside the cover stamping. As the name suggests, lever style applications use forged or stamped levers as the primary release mechanism. In addition to coil springs and levers, typical lever assemblies are comprised of a pressure plate, eyebolts, eyebolt nuts, eyebolt washers, eyebolt pins, and a cover stamping.

When the clutch pedal is depressed, pressure is applied against the tips of the levers and they are pushed toward the flywheel. The opposite end of the levers pivot away from the flywheel which pulls the pressure plate away from the flywheel.

The clamp load of lever style assemblies is easily altered by varying the number of coil springs used and/or using coil springs with different spring pressure. When combined with the fact that coil springs are readily available and relatively inexpensive to produce, it’s understandable why lever style applications are commonly used in earlier applications that may endure a variety of driving conditions.

Diaphragm Style
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 round 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.

Just like lever assemblies, when the clutch pedal is depressed, the release bearing applies pressure 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 flywheel. The pressure plate is then pulled away from the flywheel by the use of diaphragm straps that connect the pressure plate to the cover stamping.Unlike lever assemblies that lose clamping force as the friction material of the disc wears thinner, 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. Due to these advantages, newer passenger car and light-duty applications utilize diaphragm style assemblies.

During recent years, several new diaphragm style designs have been developed. Each design is engineered to address issues relative to specific applications and driving styles.

Crimped cover assembly – Rather than using rivets to connect the cover stamping and diaphragm spring, the cover stamping has been formed and crimped in a way, that the stamping itself holds the diaphragm spring in place. The crimped design also initially compensates for wear.

Self-adjusting assembly - This design uses a spring-loaded, self-adjusting, wedged ring (inside the cover stamping) that rotates to maintain constant diaphragm spring height and pedal effort. As the friction material on the disc wears thinner, the tapered wedged ring rotates, utilizing a thicker section of the ring to compensate. Each self-adjusting assembly must be matched with a special disc design that features a double layer of cushion segments. These segments assist in disengaging the pressure plate while aiding rotation of the wedged ring.

Keyhole assembly – A series of keyhole-shaped tab cutouts are made into the top section of the cover stamping. The spring-loaded tabs maintain tension on the diaphragm spring in order to compensate for wear at the pivot point of the diaphragm spring and pivot ring. This design reduces the chances of no-release later in the service life of the pressure plate assembly.

Modular assembly – Utilizing a variety of diaphragm style assemblies, the modular assembly consists of a diaphragm assembly, disc assembly, AND flywheel that have been riveted together to create a single system. This eliminates potential misalignment, contamination of the disc friction material, and non-compatibility of components while reducing installation time.

Pull-type assembly – This design is unique because the release bearing is actually attached to the diaphragm spring, and the actuation system is engineered to pull the release bearing away from the pressure plate. Because pull type assemblies typically offer higher clamp loads compared to other diaphragm style assemblies of equal size, they have commonly been used in high-performance sports cars ranging from Porsche applications to General Motors' Corvette. However, because of their rugged design and performance characteristics, pull type assemblies are gaining popularity in mid-size and compact sports sedans.

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