ASE A5 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

DOT 5 brake fluid

Silicone-based fluid that is not hygroscopic and must never be mixed with glycol-ether DOT 3, DOT 4, or DOT 5.1 fluids, because mixing causes seal swelling and system damage.

Sinking brake pedal

With steady pressure applied and no visible external leak, a pedal that slowly sinks toward the floor indicates an internal leak past the master cylinder piston cup seals.

Residual pressure valve

A spring valve at the master cylinder outlet that holds a small pressure in the lines; about 10 psi is used with drum brakes to keep wheel cylinder cups seated.

Metering valve function

Also called a hold-off valve, it delays front disc brake application until rear drum pressure builds, typically around 100 psi, to limit nose dive on light stops.

Bench bleeding a master cylinder

A procedure that pushes fluid through the master cylinder on the bench before installation so trapped air is expelled and the pedal does not stay spongy.

Compensating port blockage

An overlong or misadjusted booster pushrod can cover the master cylinder compensating port, trapping fluid as it warms and causing brake drag and overheating.

Duo-servo brake action

A drum brake design in which the primary shoe's rotation is transferred through the star-wheel adjuster to the secondary shoe, greatly increasing self-energizing force and stopping power.

Drum maximum diameter

The largest allowable inside diameter, stamped on the drum; a drum worn or machined beyond this limit must be replaced because it will not dissipate heat or fit shoes correctly.

Wheel cylinder leak symptom

Brake fluid weeping past the wheel cylinder cups contaminates the linings, causing pulling, grabbing, or reduced friction; the cylinder and both sides' shoes should be replaced.

Brake shoe adjuster star wheel

A threaded adjuster that increases or decreases shoe-to-drum clearance when turned; the self-adjuster actuator lever rotates it during reversing stops on many systems.

Drum out-of-round effect

An out-of-round drum changes shoe contact as it rotates, producing pedal pulsation, uneven braking, and noise; it is measured with an inside micrometer or dial gauge.

Rotor minimum thickness

A dimension stamped on the rotor hat or hub; machining or wear below this value leaves too little metal for heat absorption and the rotor must be replaced.

Lateral runout

Side-to-side wobble of the rotor measured with a dial indicator perpendicular to the friction surface; excessive runout pushes the pads apart and causes pulsation and pedal kickback.

Disc thickness variation

Uneven rotor thickness around its circumference, caused by runout plus pad wear or uneven lug torque; it produces a pulsating pedal with no steering wheel shake.

Square-cut piston seal

The caliper seal that both seals pressure and twists to retract the piston slightly when pressure releases, maintaining pad clearance without a return spring.

Floating caliper guide pins

Sliding pins that let the caliper center itself over the rotor; they must be cleaned and lubricated with high-temperature silicone grease or the pads wear tapered.

Pad taper wear cause

Uneven thickness across a pad comes from a sticking caliper piston or binding guide pins; the caliper must be serviced rather than only replacing the pads.

Booster operational test

With the engine off, pump the pedal to exhaust vacuum, hold it, then start the engine; a working vacuum booster lets the pedal drop slightly as assist begins.

Booster leak test

Run the engine, hold the brake pedal, then shut the engine off; the pedal should hold its position for about 30 seconds if the booster and check valve seal.

Vacuum check valve

A one-way valve at the booster that traps engine vacuum when the engine is off, providing reserve assisted stops and preventing backfire pressure from entering the booster.

Hydro-boost power source

A hydraulic assist unit that uses pressure from the power steering pump, typically over 1,000 psi, and stores reserve pressure in a nitrogen-charged accumulator.

Booster pushrod adjustment

The gap between the booster pushrod and master cylinder piston is set with a gauge; too long a rod preloads the master cylinder and causes brakes to drag.

Wheel bearing endplay

Axial clearance in a tapered roller bearing hub, usually set between 0.001 and 0.005 inch by adjusting the spindle nut; sealed hub units are simply torqued.

Parking brake service mode

A scan-tool-commanded state on electric parking brake systems that retracts the caliper pistons so rear pads and rotors can be replaced without damage.

Drum-in-hat parking brake

A small drum brake assembly located inside the hat of a rear disc rotor, used as a parking brake and adjusted through a hole in the backing plate.

Collapsed brake hose

A hose whose inner liner separates and acts as a one-way valve, holding pressure at the caliper so the brake drags and the wheel overheats.

Lug nut torque effect

Uneven or over-torqued lug nuts distort the rotor and hub, creating lateral runout and thickness variation that shows up as pedal pulsation.

Inductive wheel speed sensor

A two-wire sensor with a coil that generates an AC sine wave as tone ring teeth pass it; resistance is typically 800 to 1,500 ohms.

Active wheel speed sensor

A sensor that receives a power supply from the ABS module and outputs a digital square wave; it can detect zero speed and direction of rotation.

ABS lamp illuminated

The ABS warning lamp indicates the antilock system is disabled because of a fault; conventional hydraulic braking still works, so the vehicle remains safely stoppable.

HCU scan tool bleed

A service function that cycles the ABS pump and solenoid valves to push trapped air out of the hydraulic control unit, which manual pedal bleeding may not remove.

Steering angle sensor calibration

A relearn procedure performed after an alignment or steering component replacement so the stability control module knows the straight-ahead position for accurate yaw correction.