SG4247

Shadow, they are not really shim plates.

They are steel plates, that go between the clutch friction plates.

When you install Exedy or Alto or Raybestos aftermarket high performance clutch friction plates, they are generally a different thickness than the OEM clutch friction plate. Usually they are thicker, to handle more torque and heat.

So, when you stack up a clutch pack in an AT, the assembly order is steel, friction, steel, friction, etc until the drum is full. If the final stack up clearance is wrong, which it generally is with the use of aftermarket hi-per frictions, the clearance is then corrected by machining some or all of the steel plates - or the pack retaining plate - to a different thickness, or using a special "thin" plate, to get the desired total clutch pack clearance.

This clearance is critical, too tight and the pack will drag and burn itself, too loose and the trans wont shift cleanly and may burn the pack due to engine rpm flare up.

This is not something easy to do. Hence the reason it is an "in house" only deal, and only very experienced AT trans builders should attempt.