Two sets of plates make up the clutch pack. These are driving plates and driven plates.
The outer driving plates are flat and have external splines that locate in mating splines in the clutch drum.
The inner driven plates have a friction material bonded to them and their splines mate with splines on the outside of a central hub, which is itself splined to the primary sun gear.
The friction material can be of treated paper or fibre and may have a grooved surface to assist in wiping oil from between the plates when the clutch engages.
The plates are placed alternately to make up the pack and are loaded into the clutch drum against the relatively thick pressure plate.
The central hub is installed to engage the inner plates and thrust washers are placed in position prior to installing the input shaft.
The large face of the input shaft acts as the final plate in the pack while the splines at its outer edge transmit the input torque to the clutch drum and the driving plates. The input shaft is retained in the drum by a large diameter snap ring.
The number of plates installed determines the torque capacity of the clutch. Installing more plates increases the torque capacity, but in all cases the clutch must maintain its specified clearance so that the plates can separate from one another while in the released position.
A centrifugal relief valve in the clutch piston releases fluid trapped in the cylinder when the clutch is released. This prevents partial application of the clutch which may be caused by centrifugal force acting on the fluid at high speed.
