applications use lever style assemblies while most late model applications use diaphragm style assemblies. Both provide the same mechanical function, however, they differ in terms of the type of release mechanism used for engagement and disengagement.

Lever Style pressure plate assemblies produce clamp load with pressure from coil springs. 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, compressing the coil springs, 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 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.

Just like lever assemblies, when the clutch pedal is depressed, 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 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, most 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.

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As indicated, pressure plate assemblies are engineered in a variety of designs, each utilizing a multitude of precisely manufactured components, all of which are intended to increase the overall function and service life of a clutch system. Simply put, production methods and materials from off-shore sources like China and India, just don’t measure up. Heat treating, specification variance, material density, assembly procedures, and engineering analysis all fail to meet the necessary O.E.M. criterion. As a result, few of these look-alike “knockoffs” fail to provide even minimum service life standards.

What’s more, vehicle manufacturers may rely on more than one O.E. manufacturer to provide pressure plate assemblies for the same make and model year vehicle. In other instances, O.E. manufacturers will tool up an aftermarket version of the O.E. design. This leads to issues of compatibility in the automotive aftermarket because the designs from one O.E. manufacturer aren’t necessarily compatible with the designs of another O.E. manufacturer.

Because AMS is the premier independent supplier to the automotive aftermarket, we’ve resolved these issues. Our offering of pressure plate assemblies is comprised of the highest quality units available, produced exclusively by select O.E. manufacturers. We test each pressure plate for lift-off, balance, clamp load, release load, and parallelism. Our extensive IDD compatibility analysis procedures (see IDD section for more details) ensure optimum functionality with the other driveline components.

In addition, we never recommend or catalog lower grade components that meet dimensional specifications, but fail to address issues specific to the application. As an example, we catalog both lever and diaphragm style assemblies for certain applications. Offering our customers a choice, better enables them to meet the demands of specific driving conditions.

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