Free play is the clearance between the brake pedal linkage and master cylinder piston.
Brake pedal travel is the distance from its rest position to its applied height.
Check the master cylinder for leaks if: the brake fluid is low in the reservoir, the brake warning light is on, or the brake pedal reserve height is too low.
Inspect the master cylinder for internal leaks only if the brake pedal sinks.
Bench bleed the master cylinder prior to installing it to minimize time needed to bleed the hydraulic brake system.
Master cylinder pushrod length should only be adjusted if: someone changed the adjustment setting, the brake pedal linkage has been repaired or adjusted, or the power booster is being replaced.
Brake lines are made of double-walled steel and coated to help resist corrosion.
Damaged brake lines should be replaced not repaired; always use the correct tubing bender to avoid kinks.
The two types of brake line flares are inverted double and ISO.
Brake hoses transmit the brake system hydraulic pressures to the wheel units and must be of the proper length to be effective.
Pinching or kinking a brake hose can cause it to fail.
Inspect brake hoses for: cracks, bulges, abrasion or wear, kinks, and internal breakdown.
Hydraulic braking systems use proportioning valves, metering valves, pressure differential valves, or anti-lock hydraulic control units to modify hydraulic pressure.
Proportioning valves reduce brake pressure to the rear wheels and are pressure-sensitive or load-sensitive.
Load-sensitive proportioning valves adjust rear brake pressure according to the weight of the vehicle’s load.
Pressure-sensitive proportioning valves use a poppet piston to limit the rate of braking pressure increase to the rear brakes.
Metering valves work to ensure rear brake pressure is applied before front brake pressure.
The combination valve combines individually operating proportioning valves, metering valve and pressure differential valve in one unit and cannot be repaired.
Brake warning lights alert drivers to: engagement of the parking brake, low brake fluid intake, and unequal pressure in the hydraulic brake system.
Stop lights are mounted on the rear of a vehicle and alert other drivers that the vehicle is being braked.
As of 1986, all vehicles must have a center highmount stop lamp (CHMSL) to reduce incidence of rear-end collisions.
Power brake units are either vacuum assist (most common) or hydraulic assist.
Vacuum boosters have single or dual diaphragms to extract power from atmospheric pressure and transmit force to the master cylinder.
A 12-inch vacuum booster is capable of generating enough psi to stop a vehicle weighing thousands of pounds.
A vacuum booster works off of the difference between manifold vacuum and atmospheric pressure; a difference in these pressures creates more force on the master cylinder pistons.
Inspect and test power brake systems whenever the customer complains that the brakes are dragging, the brake pedal is harder to push than normal, the pedal height has changed, or the engine operation changes more than a minimal amount when the brake pedal is applied.