Clutch Disc Assembly information - Automotive Parts Network

The disc assembly is mounted to the input shaft, between the pressure plate assembly and the flywheel. During engagement, the disc slides forward on the input shaft and becomes solidly clamped, or “engaged”, between the flywheel and the pressure plate assembly. During disengagement, the disc is no longer engaged. Although the pressure plate assembly and flywheel continue rotating, the input shaft and disc are no longer being rotated by the engine.

A typical disc assembly is comprised of friction material, marcel segments, torsional springs, stop pins, rivets, a hub flange, a drive plate, and a retainer plate. The friction material is riveted to numerous marcel or “cushion” segments. The segments are made from heat-treated, stamped, spring steel and a wave is formed in them during the stamping process. The wave softens engagement and minimizes chatter when the pressure plate forces the disc in contact with the flywheel. Each segment is riveted to the retainer plate, which is exposed on the flywheel side of the disc. The hub flange is located in the center of the disc between the retainer plate and a drive plate that is exposed on the pressure plate side of the disc. The splines on the hub match the splines on the input shaft. Torsional springs nestled around the hub flange absorb shock during engagement.

Rigid disc assembly – A rigid disc utilizes a splined hub-flange riveted or welded to the drive plate. The drive plate may be used as the mounting surface for the friction material, but more commonly friction material is mounted to marcel segments that are riveted to the drive plate. The use of a rigid disc in automotive and light truck applications is normally limited to vehicles with less than 50 horsepower and/or vehicles where the torsional dampening capacity has been transferred to a Dual Mass flywheel (DMF).

Single stage disc assembly - This disc is used in the vast majority of pre-1990 automotive and light truck applications, both domestic and import. A single stage disc uses three to ten torsional springs around the hub flange, in order to control the heavier torsional loads generated by engines with more than 50 horsepower. This disc typically has six to ten degrees of torsional spring dampening capacity. The single stage terminology is derived from the fact that the damper springs all work simultaneously with hub flange movement.

Idle stage damper disc assembly – Certain applications require a disc that includes an "idle stage damper". Each damper is comprised of a series of friction washers located inside the disc, or a series of small secondary springs located between the hub and the torsional springs. The idle stage damper is engineered to dampen damaging torsional spikes caused by engine vibration (primarily during start-up and shut-down) which can destroy transmission gears. It also reduces drivetrain vibration and silences transmission gear noise at engine idle. An idle stage damper disc typically has up to three degrees of idle stage damper movement, along with the six to ten degrees of torsional spring damper capacity.

Series damper disc assembly – Still other applications require a disc with an even greater ability to eliminate noise and dampen torsional vibrations. In these instances, a "series damper" disc is used, which contains two rows of coil springs that compress in a sequential series. When the disc first engages, the outer row of springs compress, and then the inner row of springs compress as needed. A series damper disc can have up to 20 degrees of torsional spring dampening capacity.
AMS Content
As we’ve shown, each O.E.M. disc assembly is engineered to fit within a series of size and weight parameters that are based on desired levels of fuel consumption, driver comfort, torque capacity, and vibration suppression. In order to address the specific requirements of each application, AMS relies exclusively on disc assemblies produced by O.E. suppliers like Aisin, AP, Atsugi, Daikin, LuK, NKK, Paraut, Valeo, and Valeo PH.

While offshore “knockoff” discs may appear identical, rotary fatigue tests prove otherwise. By relying primarily on dimensional specifications, suppliers of aftermarket knockoffs fail to ensure that the replacement disc will meet the necessary functional criterion. In almost all instances, these look-alike discs fail to meet even the minimum O.E. standards set at 1,000,000 engagements. Hub flanges, torsional springs, retainer plates, and cover plates all failed at less than 28% of the minimum criterion during testing.

As is the case with pressure plate assemblies, vehicle manufacturers may rely on more than one O.E. producer to provide disc assemblies for the same make and model year vehicle. Additionally, other O.E. producers will tool up an aftermarket design, leading to non-compatibility issues with mating components.

Sorting through these issues requires extensive testing and impartiality. Each AMS disc is tested for dimensional and functional characteristics including lateral run-out (flatness), marcel deflection (compression), torsion durability, spring rate, and material density. This information is then cross-referenced using IDD compatibility analysis (see IDD section for more details). What’s more, our status as an independent supplier guarantees that we aren’t tied to defective designs and/or obsolete tooling. Whereas other suppliers may continue to supply substandard and defective components, simply to recoup fixed PP&E costs and tooling costs, we simply chose the best designs from the best suppliers.

Finally, our cataloging reflects the high standards set forth by vehicle manufacturers. Each application listing is based on the functional requirements used in the vehicle when it was new. Dimensionally similar substitutes simply aren’t allowed as replacements in applications that require innovative designs and materials to address performance characteristics. For example, General Motors uses the same pressure plate assembly in gas and diesel applications because the clamp load requirements, torque capacity, and release characteristics need not change. However, the diesel application requires a disc design that will dampen torsional spikes, reduce drivetrain vibration, and silence transmission gear rattle. While the dimensional characteristics of the "gas engine" disc are identical to the dimensional characteristics of the "diesel engine" disc (both are compatible with the same pressure plate assembly), use of a "gas engine" disc in the diesel application will eventually result in premature clutch system failure or damage to the transmission.