Riviera V6-3.8L SC VIN 1 (1995)
Fig. 11 Proportioners Installed In Master Cylinder
During rapid deceleration, a portion of vehicle weight is transferred to the front wheels. This resultant loss of weight at rear wheels must be
compensated for to avoid early rear wheel skid. The proportioner or pressure control valve reduces rear brake system pressure, delaying rear wheel
skid. When the proportioner or pressure control valve is incorporated in the combination valve assembly, pressure developed within the valve acts
against the large end of the piston, overcoming the spring pressure, moving the piston left, Fig. 9. The piston then contacts the stem seat and restricts
line pressure through the valve.
During normal braking operation, the proportioner or pressure control valve is not functional. Brake fluid flows into the proportioner or pressure
control valve between the piston center hole and the valve stem, through the stop plate and to the rear brakes. Spring pressure loads the piston during
normal braking, causing it to rest against the stop plate, Fig. 10.
On diagonally split brake systems, two proportioners or pressure control valves are used. One controls the left rear brake, the other the right rear
brake. The proportioners or pressure control valves are installed in the master cylinder rear brake outlet ports, Fig. 11.
