DIAGNOSIS & TESTING
Diagnostic Help
Brake diagnosis involves determining if the concern is related to a mechanical, hydraulic, electrical or vacuum oper-
ated component.
NOTE :
The brake reservoir fluid level will decrease in proportion to normal lining wear.
NOTE :
Brake fluid tends to darken over time. This is normal and should not be mistaken for contamination.
NOTE :
Before starting repairs which do not require battery power:
• Turn off ignition switch.
• Disconnect the negative battery terminal.
Preliminary Brake Check:
• Check the condition of the tires and wheels. Damaged wheels and worn, damaged or under inflated tires can
cause a pull, shudder, vibration and a condition similar to brake grab.
• If a complaint was based on noise while braking, check the suspension components. Jounce the front and the
rear of vehicle and listen for anything that might be caused by a loose, worn or damaged suspension or steer-
ing component.
• Inspect the brake fluid level and condition.
1. If the fluid level is abnormally low, look for any evidence of leaks at the calipers, brake lines, master cyl-
inder and at the Antilock Brake System (ABS) Hydraulic Control Unit (HCU).
2. If the fluid appears to be contaminated, drain a sample to examine.
• The system will have to be flushed if the fluid is separated into layers, or contains a substance other than
brake fluid. The system seals, cups, hoses, master cylinder and HCU will also have to be replaced after flush-
ing. Use clean brake fluid to flush the system.
• Check the parking brake operation. Verify free movement and full release of the cables and the lever. Also note
if the vehicle was being operated with the parking brake partially applied.
• Check the brake pedal operation. Verify that the pedal does not bind and has adequate free play. If the pedal
lacks free play, check the pedal and the power booster for looseness or for a binding condition. DO NOT road
test the vehicle until the condition is located and corrected.
• Check the vacuum booster check valve and vacuum supply hose.
• If the preliminary checks appear to be OK, road test the vehicle.
Brake Noise
CONDITION POSSIBLE CAUSES CORRECTION
Disc Brake Chirp
· Excessive brake rotor runout.
· Small metal particles
· Diagnose and correct as
necessary.
Disc Brake Rattle Or Clunk
· Broken or missing spring clips.
· Caliper guide pin bolts loose.
· Missing abutment shims.
· Small metal particles
· Replace brake pads
· Tighten guide pin bolts.
· Replace missing abutment shims.
Disc Brake Squeak At Low Speed
(While Applying Light Brake Pedal
Effort)
· Brake shoe linings. · Replace brake pads.
Scraping Or Whirring
· ABS wheel speed sensor hitting
tone wheel.
· Inspect, correct or replace faulty
component(s).
12–6
Chery Automobile Co., Ltd.
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