The Ford 4F50N (AX4N) converter may have weak and/or broken spring clips and a worn mating piston, causing noise in this unit. Bending or replacing the spring clips is only a temporary fix. Sonnax clutch conversion plate FD-DA-18PBF is a drop in replacement that uses the existing damper, but converts the clutch from a two- to one-friction ring piston. This eliminates the noise problem found in the OE units. This piston includes a bonded BorgWarner HTL friction ring. FD-DA-18PBF pistons can be identified by their "0" stamp.