2008 Chevrolet Express 3500 Brake Service (ONLINE REPAIR MANUALS)

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 inspected 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 hol...

Removal

• Siphon ^2/3 of the brake fluid from master cylinder.
• Raise and support vehicle.
• Remove tire and wheel assembly.
• Compress caliper pistons until they bottom in bores using suitable clamp, Fig. .
• Disconnect brake hose at caliper by removing inlet fitting bolt.
• Remove mounting bolts and caliper.

Inspection

Should it become required to remove the caliper for installation of new components, clean components in denatured alcohol, wipe dry using lint-free cloths. Blow out drilled passages and holes using compressed air. Inspect dust boots for punctures or tears. If punctures or tears are...

Manual Bleed

• If vehicle is equipped with power brakes, remove vacuum reserve by applying brakes several times with engine off.
• Fill master cylinder reservoirs with suitable brake fluid. Ensure to always keep master cylinder reservoirs at least half full during entire bleeding procedure.
• If master cylinder is suspected to have air in bore, it must be bled first. To bleed master cylinder, proceed as follows:
• Disconnect forward brake pipe connection at master cylinder.
• Allow brake fluid to fill master cylinder bore until it begins to flow from forward pipe connector port.
• Connect and ...

Delco Master Cylinder

When performing the following procedures, refer to Fig. noting that the composite reservoir may vary in design.

Disassemble

• Remove master cylinder from vehicle.
• Remove reservoir cover and diaphragm. Discard old brake fluid in reservoir.
• Inspect cover and diaphragm. Replace if cut, cracked or deformed.
• Remove fluid level switch and proportioning valve assembly, if equipped.
• Depress primary piston and remove lock ring.
• Plug primary fluid outlet (outlet nearest to cowl when master cylinder is installed), then apply compressed air into secondary fluid outlet to remo...

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, ensure 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 fails, the brak...

Accessing Diagnostic Trouble Code

Connect a suitably programmed scan tool to Data Link Connector (DLC) and follow manufacturers instructions.

Diagnostic Trouble Code Interpretation

Refer to "Diagnostic Tests" for trouble code identification.

Connector Pin Identification

Refer to Figs. through for connector pin identification.

Diagnostic Tests

Tahoe & Yukon Hybrid

Envoy, Rainier & Trailblazer

Express & Savana

Sierra & Silverado Classic

Symptom Tests

Tahoe & Yukon Hybrid

2008

Refer to Figs. and for symptom tests.

Envoy, Rainier & Trailblazer

Refer to Figs. through for symptom tests.

Expre...