1991 Chevrolet K3500 Pickup Brake Service (ONLINE REPAIR MANUALS)

HARD PEDAL

• Internal vacuum leak.
• Faulty control valve.
• Broken or damaged hydraulic brake lines.
• Collapsed or damaged vacuum hose.
• Plugged or loose vacuum fitting.
• Bad stud welds on front or rear housing on power head.
• Faulty booster diaphragm.
• Restricted air filter element.
• Worn or distorted reaction plate or levers.
• Cracked or broken pow...

EXCEPT TRACKER & 1990-91 C & K SERIES w/NON-SERVO BRAKES

• Raise and support vehicle, then remove tire and wheel assembly.
• Remove brake drum. If brake lining is dragging on brake drum, back off brake adjustment by rotating adjustment screw. Refer to individual truck chapter for procedure. If brake drum is rusted or corroded to axle flange and cannot be removed, lightly tap flange to drum mounting surface with a suitable hammer.
• Using brake spring pliers or equivalent, unhook primary and secondary return springs, Figs. through . Observe location of brake parts being removed to aid during ins...

The height sensing proportioning valve must be adjusted whenever the valve and/or linkage is disassembled or removed for service. In addition, adjustment should be checked if excessive front wheel lock-up is experienced with a lower than desired brake application rate when vehicle is at or near maximum GVWR.

• Raise and support vehicle leaving wheels on, and allow axle to hang free (no load condition).
• Remove lever retaining nut and disconnect lever from valve shaft, Fig. .
• Rotate valve shaft to permit installation of correct adjustment gauge, Fig. ,...

EXCEPT TRACKER, 1990-91 C & K SERIES w/NON-SERVO BRAKES

• Lubricate parking brake lever fulcrum with suitable brake lube, then attach lever to brake shoe. Ensure lever operates smoothly.
• Connect brake shoes with adjusting screw spring, then position adjusting screw. Ensure adjusting screw star wheel does not contact adjusting screw spring after installation, and also ensure RH thread adjusting screw is installed on left side of vehicle and LH thread adjusting screw is installed on right side of vehicle. When brake shoe installation is completed, ensure star wheel lines up with adjustin...

WIRING DIAGRAMS

Refer to "Wiring Diagrams" in "Vehicle Systems."

DIAGNOSTIC CIRCUIT CHECK

Refer to Figs. and for diagnostic circuit checks.

READING CODES

Trouble codes may be read with the TECH 1 scanner or by jumping terminal "H " of the ALDL to terminal "A" of the ALDL while observing the flashing of the "Anti-Lock" warning lamp. The terminals must be jumped for a few seconds before the code will begin.""

DIAGNOSTIC TESTS

CLEARING CODES

If the "Anti-Lock" warning lamp stays lit, the codes may be cleared with the TECH 1 scanner or by the following procedu...

Certain general service procedures apply, regardless of whether the brakes are vacuum or hydraulically assisted. Only top quality, clean brake fluid should be used. More seals and valves are used with power brake systems than with ordinary brakes, so an inferior brake fluid will do much more damage. For the same reason, be sure all dirt is kept out of the system. Additionally, on models with hydraulic assist brakes, care must be taken not to mix the fluids of the booster hydraulic system and brake hydraulic system as the fluids are not compatible.

If the power unit fai...