There are 2 forward apply pistons used in the 2004R. The most common is the stamped steel apply piston with the stamped .030 apply ring. The contact area is lower than center. This causes uneven apply of the Forward clutch pack that results in coning of the clutch pack, premature wear and loss of apply area.
The Billet Aluminum forward apply piston has an apply area of .500 and utilizes full contact. This spreads the apply over the entire surface of the steels and backing plate, preventing coning of the clutch pack while extending clutch life and HP capacity.
The Aluminum Piston is lighter and reacts quicker. A must for Hi HP applications.
The other piston that is used is a factory cast aluminum apply piston. The factory cast aluminum piston offers the increased apply surface but suffers from cracking at pressures over 225psi. The Billet Aluminum piston WILL NOT CRACK at any pressure.