See Figure 1
The 1979-86 models are equipped with a Blend Proportioning Valve (BPV). The BPV is located on the left rear frame near the rear axle for the 1979-86 models. Not all of these Pick-ups are equipped with BPV's; some are equipped with a load sensing proportioning valve.
The BPV cannot be adjusted, however, if the vehicle is exhibiting strange or dangerous braking tendencies, have the BPV tested at a reputable automotive service center. If the BPV is faulty it will have to be replaced with a new unit.
The blend proportioning valve is designed to improve efficiency within normal braking range by distributing braking force most effectively to the front and rear wheels. It also increases the braking force to the rear wheels by releasing decompressing effect if a large braking force is required, the vehicle is loaded, or in the event that a front brake line should burst.
REMOVAL & INSTALLATION
Disconnect the brake lines from the valve. Remove the mounting bolt(s) and remove the unit. Replace the proportioning valve with one having the same numerical code, only. Install the mounting bolt(s) and connect all four brake lines, tightening the flare nuts to 9-12 ft. lbs. (12-16 Nm). Bleed the system thoroughly.