Proper front and rear pressure is necessary to make the disc brakes work up to their potential. To get full pressure to the rear calipers, the proportioning valve must be modified. This valve meters and proportions brake pressure during heavy brake application and limits the pressure rise to the rear brakes. After the rear brake line is removed, the valve is taken apart and the seal and spring are taken off the piston. The piston is then put back in the valve, the end nut snugged up, and the rear line reattached.