1999 GMC K1500 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...

Height Sensing Proportioning Valve

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, leave wheels on and allow axle to hang freely.
• Remove lever retaining nut and disconnect lever from valve shaft, Fig. .
• Rotate valve shaft to permit installation of correct adjustment gauge, Fig. , ensure D shaped ho...

This system is used on all models except Montana, Silhouette, Tracker, Trans Sport and Venture. On 2000 S & T Series , four door utility vehicles can be equipped with either a 310 or 325 ABS system. Pickups and two-door utility vehicles are equipped with 310 ABS systems. While both systems are functionally the same, the 310 differs in size and appearance from the 325. It is designed to reduce the occurrence of wheel lock-up during severe braking conditions. To accomplish this function, the system regulates hydraulic brake line pressure by using an Electro-Hydraulic Control Unit (EHC...

When working on or around brake assemblies, care must be taken to prevent breathing asbestos dust, as many manufacturers incorporate asbestos fibers in the production of brake linings. During routine service operations, the amount of asbestos dust from brake lining wear is at a low level because of a chemical breakdown during use and a few precautions will minimize exposure. Do not sand or grind brake linings unless suitable local exhaust ventilation equipment is used to prevent ...

In order to properly service power brake systems, a thorough understanding of the power assist system is necessary. These systems provide a mechanical assist, acting to increase the force applied to the master cylinder piston by the driver while decreasing the effort necessary to obtain acceptable stopping performance.

Hydraulic assist units incorporate a basic open center spool valve, hydraulic cylinder and an accumulator assembly in a common housing. When the brake pedal is depressed, the hydraulic piston moves forward closing off fluid relief passages, the spool valve applies flui...

Battery Ground Cable

Prior to service disconnect battery ground cable and isolate as required.

Radio Security System

Theftlock

If the Theftlock system is active when battery power is interrupted, the customers security code must be entered to restore proper function of the radio. To unlock a secured radio after power loss, proceed as follows:

• "LOC" appears with ignition in On position.
• Press "NM" and "000" will appear on display.
• Press "NM" again to make last two digits agree with security code.
• Press "HR" to make first 1 or 2 digits agree with security code.
• Press "AM-FM" to select code entered. "SEC" wi...