Check the brake master cylinder and proportioning valves
DESCRIPTION & OPERATION
Hydraulic system is diagonally split so system will still operate if one side loses pressure. Proportioning valves (one in each rear brakeline) limit hydraulic pressure applied to rear brakes, directing most of the available hydraulic pressure to the front brakes. See Fig. 2. Valves are rearward of right front wheelwell.
Disc brakes are continually self-adjusting. Caliper piston seals retract pistons enough to allow brake lining to lightly brush rotor. Sliding caliper compensates for lining wear.
Parking brake mechanism is part of rear caliper. BRAKE warning light comes on under the following conditions:
Parking brake is not fully released.
Fluid level in master cylinder reservoir is low.
Ignition switch is in START (bulb check) position. Light should not come on with ignition switch in any other position.
BLEEDING BRAKE SYSTEM
CAUTION:Because of brake fluid expansion due to heat absorbed from brakes and engine, DO NOT overfill master cylinder reservoir. DO NOT reuse brake fluid. Use only new, clean DOT 3 brake fluid. DO NOT use silicone DOT 5 brake fluid.
NOTE:Check brake fluid level frequently during bleeding procedure.
MANUAL BLEEDING
NOTE:If BPM valve has been replaced, or it is suspected that air has been ingested into the system secondary circuits due to low fluid condition, auto bleed procedure must be performed. See ANTI-LOCK BRAKE SYSTEM & TRACTION CONTROL article.
Deplete vacuum reserve from power brake booster by depressing brake pedal several times with engine off. Fill master cylinder and keep at least half full during bleeding procedure. If master cylinder is known to not have air in bore, go to step 4). If master cylinder is known or suspected to have air in bore, go to next step.
Loosen forward brakeline fitting at master cylinder until fluid begins to flow from fitting. Tighten fitting. Have an assistant slowly depress brake pedal one time and hold. Loosen forward fitting to purge air from bore. Tighten fitting while pedal is still at floor. Release brake pedal slowly. Wait 15 seconds.
Repeat step 2) until fluid is clear and free of air bubbles. Repeat procedure at rearward brakeline fitting on master cylinder until air is purged from bore. Master cylinder is now bled. Tighten fitting to specifications. See TORQUE SPECIFICATIONS. If calipers are known to not have air in them, it is not necessary to bleed them.
NOTE:Individual calipers can be bled only after all air is removed from master cylinder.
If calipers are known or suspected to have air in them, raise and support vehicle. Remove bleeder valve cap from first bleeder valve to be serviced. See BRAKELINE BLEEDING SEQUENCE table. Place wrench over bleeder valve. Attach clear vinyl bleeder hose onto bleeder valve. Place other end of hose in clean transparent container.
Partially fill container with clean brake fluid so end of hose is submerged in fluid. Open bleeder valve 1-2 turns. Slowly depress brake pedal through its full travel one time and hold.
Close bleeder valve and release pedal. Wait 15 seconds and repeat procedure until fluid is clear and free of air bubbles. Repeat procedure on remaining bleeder valves.
NOTE:Use slow full strokes when pumping brake pedal. Rapid pumping of brake pedal will make procedure more difficult.
Ensure brake pedal feels firm and constant, not spongy. Pressure bleed system using Tech 1 scan tool "Auto Bleed" sequence, repeat steps 4 through 6. If pedal travel is not excessive, start engine. Recheck brake pedal again for firmness and no sponginess. If brake pedal is okay, road test
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Monday, October 18th, 2010 AT 3:08 AM
