Multiple Disk Clutch Assembly
Automatic transmission multiple disc clutch assemblies are wet clutches that drive and hold the planetary gearset members. Friction discs are splined on the inside, fastening them to one member of the set, a hub, or a drum. They are cellulose, with grooves cut into their surface to aid in heat dissipation or semi-metallic or metallic materials. Metal friction discs wear their mating steel plates sooner than paper discs. Steel separator plates are splined on the outside and slide on the splines/lugs inside the case or drum.
Multiple Disk Clutch Components
When a clutch is case held, the outer splines slide into slots in the transmission case. When the clutch assembly is applied, a member is locked to the case. This type of clutch is considered case held, grounded, or "locked." A spring or set of springs returns the piston assembly to its parked position when hydraulic pressure is released.
Some residual pressure is left after the venting of the hydraulic pressure. It's released through a vent and check ball or a controlled orifice located inside the drum. Typically if the ball doesn't rattle around when the drum is shaken, it's stuck from tarnish. This problem results in excess pressure on the clutch and premature wear.
Clutch Friction Discs
When disassembling a transmission, it's important not to mix the parts of one clutch pack with another. Always inspect and clean the assemblies after removal. Typically friction discs are soaked in clean transmission fluid for about 20 minutes before reassembly. The soaking protects them during initial use. Review manufacturer specifications for proper clutch pack clearances, TSB's, or special test procedures.