Brake performance is mainly affected by three things: the level and condition of the brake fluid, the system's ability to create and maintain hydraulic pressure, and the condition of the friction components.
Air in the brake fluid will make the brake pedal feel spongy during braking or will increase the brake pedal force required to stop. Fluid contaminated by moisture or dirt can corrode the system. Inspect the brake fluid inside the reservoir. If it is dirty or murky, or is over a year old, the fluid should be replaced.
Visually check the hydraulic system starting at the master cylinder. To check the function of the master cylinder hold the brake pedal down hard with the car stopped and the engine running. The pedal should feel solid and stay solid. If the pedal slowly falls to the floor, either the master cylinder is leaking internally, or fluid is escaping from other points in the system. If no leaks can be found, the master cylinder is faulty and should be replaced. Check all brake fluid lines and couplings for leaks, kinks, chafing or corrosion.
Check the brake booster by pumping the brake pedal approximately 10 times with the engine off. Then hold the pedal down and start the engine. The pedal should fall slightly. If not, check for any visible faults before suspecting a faulty brake booster, and check the non-return valve for one-way flow.
- The brake booster non-return valve is in the vacuum hose at the left side manifold, in the engine compartment.
• See 400 Suspension, Brakes and Steering-General for a brake troubleshooting table.
• See 470 Brakes-Hydraulic for repair information for hydraulic brake components or the brake power-booster.
Worn or contaminated brake pads will cause poor braking performance. Oil-contaminated or glazed pads cannot produce as much friction, and stopping distances will increase. Inspect the rotors for glazing, discoloration, scoring or oili-ness.
Steering wheel vibration while braking at speed is often caused by warped brake rotors, but can also be caused by worn suspension parts.
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