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Plates of Different Thickness in the Clutch Drum

February 5, 2015

When installing steel plates of different thickness in a clutch drum, the placement of the thinner plates can be important. And, the ideal placement of those plates depends on which clutch drum you’re using.

Steel plates are often used to adjust clutch pack clearance or increase clutch pack space to add additional friction and steel plates for more capacity. To properly place the plates, you must know whether the clutch drum works as a holding clutch or a shifting clutch.

A holding clutch or static clutch, such as a reverse or forward clutch, applies and transfers torque usually while the vehicle is at rest. So, under normal driving conditions, they are typically not engaging or disengaging. The number of times a holding clutch applies is significantly lower than if it were to be used in a shifting application. A holding clutch needs to hold and transfer torque. When applied, very little heat is generated within the clutch pack; therefore, thinner steel plates can be used anywhere in the clutch pack. Typical holding clutch failures result from insufficient torque capacity, hydraulic pressure leaks or pressure control issues. Forward-to-reverse abuse also contributes to failure.

An example of a shifting clutch or dynamic clutch is an intermediate clutch or a 3-4 clutch. A dynamic clutch needs to transfer torque by coupling an inner hub to an outer hub, each rotating at different RPMs, during a gear ratio change or shift. During a shift, shifting clutches transfer larger amounts of energy than a static clutch. Therefore, a greater amount of heat is generated during clutch apply, which produces higher temperatures at the friction and steel surfaces. The longer the slip, the higher the temperature climbs – making the engagement time a critical factor. In addition, the typical clutch pack with double-sided frictions creates heat input on both sides of a steel plate during an engagement. The steel plate needs to absorb and dissipate the head without warping, hot spotting or coning. The ability to do so is related to its thickness or mass.

During the shift, the temperature rise is generally higher in the center of the clutch pack than at either end, which makes it better to place thinner steels away from the center. Placing them against the apply piston or backing plate, where temperature is limited, is the best advice. That’s why specialty clutch packs that include all thin steel plates, so you can add more clutches, actually overheat and fail sooner than stock plates. There’s a lot of engineering needed to balance performance AND durability.

posted by: Addy Ministrator   comments: 0