Your FREE ASE A5 Flashcards 2026 – 200+ Cards

Converts brake-pedal force into hydraulic pressure. A tandem (dual) design feeds two separate circuits so one leak still leaves half the brakes working.

A master cylinder with two pistons that feed two independent hydraulic circuits, providing a safety backup if one circuit leaks.

Pressure applied to a confined fluid is transmitted equally in all directions, letting a small pedal force become large clamping force at every wheel.

Hydraulic fluid (DOT 3, DOT 4, DOT 5.1) that transmits pedal pressure. Glycol-based fluids absorb moisture over time.

A glycol-based, hygroscopic brake fluid with a dry boiling point around 401°F (205°C). The most common factory fill.

A glycol-based, hygroscopic fluid with a higher boiling point than DOT 3; used where harder braking or ABS demands more heat resistance.

A silicone-based, non-hygroscopic fluid NOT compatible with most ABS systems; never mix it with DOT 3/4.

Describes glycol brake fluid that absorbs water from the air; moisture lowers the boiling point and promotes corrosion.

Absorbed moisture lowers the boiling point (risking fluid fade) and causes internal corrosion, so glycol fluid is flushed on a service schedule.

Forcing fluid through the system to push out trapped air that would otherwise compress and cause a soft, spongy pedal.

An assistant pumps and holds the pedal while you open and close each bleeder in sequence to expel air.

Pressurized fluid is pushed from the master cylinder reservoir through the system to expel air without pumping the pedal.

A hand or machine vacuum pump draws fluid and air out at each bleeder screw.

Open bleeders let fluid and air drip out under gravity alone; slow but needs no helper.

Usually bleed the wheel farthest from the master cylinder first, then work closer, unless the service manual specifies otherwise.

Almost always air in the hydraulic system; bleed the brakes to restore a firm pedal.

Caused by a fluid leak, worn linings, or a master cylinder leaking internally past its cups.

An internally leaking master cylinder bleeding pressure past its piston cups; replace the master cylinder.

Loss of power assist — a failed vacuum booster, leaking check valve, or no engine vacuum.

Steel tubing (often with a double flare or ISO/bubble flare) that carries pressurized fluid to the brakes; never use compression fittings.

Flexible reinforced hose connecting rigid lines to a moving wheel/caliper; can collapse internally and act as a one-way restriction.

A reinforced flare on steel brake line that folds the tubing back on itself to seal high pressure without cracking.

A metric brake-line flare that forms a rounded bubble seal; do not interchange with a double flare.

Reduces pressure to the rear brakes during hard stops to keep the rear wheels from locking before the front.

Briefly holds off front-disc pressure at low application so rear drum brakes apply at the same time, balancing braking.

Combines the metering, proportioning, and pressure-differential functions in one body, often with a brake warning switch.

Detects unequal pressure between the two hydraulic circuits and lights the red brake warning lamp if one side fails.

Maintains a small pressure in drum-brake circuits to keep wheel-cylinder cups seated and speed re-apply.

Multiplies pedal force using engine vacuum on a diaphragm so light pedal effort makes high line pressure.

A power-assist unit using intake-manifold vacuum on a diaphragm to boost braking force.

A one-way valve that traps vacuum in the booster after the engine stops, giving a reserve for a few assisted applications.

Pump the pedal off to deplete vacuum, hold it, then start the engine — the pedal should drop as assist comes in.

A power-assist system using power-steering pump hydraulic pressure instead of engine vacuum; common on diesels and heavy vehicles.

Brakes with no power assist; require higher pedal effort and have no booster to diagnose.

Applies the rear brakes mechanically (cable, drum-in-hat, or integrated caliper) independent of the hydraulics, so it works if hydraulics fail.

Set the rear base brakes to spec first, then adjust the cable at the equalizer; never mask worn linings with cable tension.

The yoke that splits parking-brake cable tension evenly to both rear wheels.

A motor-applied parking brake; many need a scan-tool service mode to retract the motor before rear-pad service.

A small drum brake inside the center of a rear disc-brake rotor that serves only as the parking brake.

Indicates low fluid, a hydraulic circuit failure (pressure differential), or the parking brake applied — not ABS.

A loss of stopping power from heat — overheated linings (mechanical fade) or boiled fluid forming vapor (fluid fade).

Overheated friction material loses its coefficient of friction, giving a hard pedal that won't stop the car.

Boiled brake fluid forms compressible vapor, giving a spongy, sinking pedal under hard or repeated braking.

The mechanism that converts the vehicle's kinetic energy into heat to slow it; brakes are essentially heat machines.

A rating of how much grip a lining provides against the rotor/drum; affects stopping power and fade resistance.

The small pedal travel before the pushrod begins to move the master-cylinder piston; too little can hold brakes applied.

Sets where braking begins; too long holds the brakes partially applied (drag); too short delays braking.

A valve at each wheel cylinder/caliper opened to let air and old fluid escape during bleeding.

Bleeding a new master cylinder on the bench before installation to remove air from its bores.

Mounted at the pedal; turns on the stop lamps when the pedal is pressed and inputs to cruise/ABS.

Each circuit serves one front and the opposite rear wheel, so a leak still leaves balanced braking on a diagonal.

Older split where one circuit serves both fronts and the other both rears.

Brake lamps warn following traffic; a burned bulb or bad switch is a safety/inspection failure.

Pedal leverage that multiplies foot force before the booster and master cylinder; part of total braking force.

The fluid container atop the master cylinder; low level warns of leaks or worn linings.

Petroleum (oil) contamination swells rubber seals and cups; the system must be flushed and seals replaced.

Residual pressure, a swollen seal, a tight pushrod, or a restricted return can hold brakes applied and overheat them.

The hydraulic cylinder in a drum brake that pushes the shoes outward against the drum (covered under drum service too).

Tapping a gauge into the system to compare line pressures and identify restrictions or low output.

A restricted (collapsed) flex hose can hold one caliper applied, dragging and pulling that side.

Rubber seals on the master-cylinder pistons; worn cups leak internally and let the pedal sink.

Manifold vacuum (or a vacuum pump on turbo/diesel engines) feeds the booster; low vacuum = weak assist.

A sudden hard, high pedal that takes much more effort to stop the car.

Dry = fresh fluid; wet = after absorbing 3.7% water — the wet point is much lower, which is why fluid is flushed.

A hollow bolt-and-eye hydraulic connection (often at a caliper) sealed with copper crush washers.

One-time sealing washers at banjo fittings; replace them whenever the fitting is opened.

Check for cracks, bulges, leaks, and internal collapse; a bad hose can cause pull, drag, or a pedal complaint.

Wet, oily linings and fluid behind the dust boot; replace the wheel cylinder and contaminated shoes.

As disc pads wear, the caliper pistons extend and fluid level drops — a slowly falling level can simply mean worn pads.

Keeps slight pressure on drum circuits; not used on disc circuits, where it would cause drag.

Dark, dirty fluid signals moisture and corrosion and the need for a flush; fresh fluid is clear to amber.

Use the DOT 3/4/5.1 glycol fluid specified; silicone DOT 5 is not used in ABS-equipped vehicles.

Without an active ABS stop, pulsation traces to rotor runout or thickness variation.

The vehicle veers to one side when braking because one side brakes harder than the other.

Proper front-to-rear and side-to-side force distribution for straight, stable stops.

The brake switch tells the ABS module the brakes are applied; a faulty switch can disable some functions.

Inspect lines, hoses, wheel cylinders, calipers, and the master cylinder; a sinking pedal with no leak = internal master-cylinder leak.

The red BRAKE lamp = hydraulic/parking-brake/fluid issue; the amber ABS lamp = electronic brake control issue.

Rigid steel lines run along the body; flexible hoses bridge to moving suspension and steering parts.

Flexes to keep air off the fluid (limiting moisture absorption) as level drops with pad wear.

Bleed drum wheel cylinders like any wheel — open the bleeder, expel air, keep the reservoir full.

A blown line/hose or massive leak; the split system should still give partial braking on the good circuit.

Always use the DOT rating and type listed in the owner's manual or on the reservoir cap.

Lets vacuum leak into the engine (rough idle) and reduces assist; replace the booster.

Because the parking brake is mechanical, it can hold the car even if the hydraulic system has failed.

The red brake lamp briefly lights at start-up to prove the bulb works, then goes out.

A wheel cylinder pushes shoes outward against a rotating drum; self-energizing, cheap, and common on rear axles.

The rotating iron drum the shoes press against; measured for inside diameter, taper, and out-of-round.

The curved friction member in a drum brake; the primary (forward) shoe usually has the shorter lining.

The hydraulic cylinder that pushes the shoes apart against the drum when the pedal is applied.

The rotating drum drags the leading shoe tighter against itself, multiplying braking force.

Both shoes wedge into the drum for strong, low-effort holding, which suits parking-brake duty.

The forward (leading) shoe, usually with the shorter lining; it actuates the secondary shoe via servo action.

The rear (trailing) shoe, usually with the longer lining; it does most of the braking work.

The largest inside diameter a drum may be worn or machined to, stamped on the drum; over it, replace the drum.

Use a drum micrometer to check inside diameter, taper, and out-of-round against the max-diameter spec.

An unevenly worn drum that isn't a true circle, causing pulsation or grab; machine or replace.

A drum worn wider at one edge than the other; checked when measuring inside diameter.

Pull the shoes back off the drum when the pedal is released; weak springs cause drag.

Keep the shoes against the backing plate while allowing them to move outward to the drum.

A screw mechanism that maintains shoe-to-drum clearance; many adjust during reverse stops.

Causes drag, overheating, and a pull or grab; back off the star wheel to spec.

Gives a low pedal and excessive travel before the brakes apply.

The stamped plate that holds the wheel cylinder, shoes, and hardware; its pads should be cleaned and lubricated.

Used through a slot in the backing plate to turn the star-wheel self-adjuster.

A non-servo design where one shoe leads and one trails; less self-energizing than dual-servo.

Replace shoes in axle sets and refinish or replace drums so both sides brake evenly.

Open the bleeder atop the wheel cylinder and expel air, keeping the reservoir full.

Fluid from a leaking wheel cylinder or grease ruins the linings; replace shoes and fix the leak.

Worn-out linings, a scored drum, or missing hardware; grinding means metal-to-metal contact.

A small drum brake in the center of a rear disc rotor used only as the parking brake.

If turning a drum to clean it would exceed the max diameter, replace the drum instead.

The strut and lever that spread the shoes when the parking-brake cable pulls.

Clamps friction pads against a spinning rotor with a caliper; cools well and resists fade, so it's used on most front brakes.

The cast-iron disc the pads clamp; checked for thickness, minimum thickness, parallelism, and runout.

The clamp housing the disc-brake pistons and pads; can be floating (sliding) or fixed.

Has pistons on only one side and slides on pins/guides so both pads clamp the rotor evenly.

Has pistons on both sides of the rotor and does not slide; common on performance vehicles.

Lubricated pins that let a floating caliper move; seized pins cause uneven pad wear and a pull.

The friction blocks a caliper presses against the rotor; replaced in axle sets.

The thinnest a rotor may safely be, cast/stamped into it; a rotor below it must be replaced.

A spec slightly thicker than discard, so a turned rotor keeps a safety margin; not the same as minimum thickness.

Side-to-side wobble of a spinning rotor, measured with a dial indicator; excess runout causes pulsation.

Uneven rotor thickness that makes clamping force rise and fall, causing pedal pulsation and shimmy.

Use a micrometer at several points around the rotor; compare to minimum and refinish specs.

Mount a dial indicator against the rotor face and rotate it to read side-to-side movement.

A rotor with internal cooling vanes between two friction faces to shed heat and resist fade.

A single-piece rotor without internal vanes, used where cooling demand is lower (often rears).

Uneven side-to-side force from a seized caliper, restricted hose, or contaminated pads.

High-frequency noise from vibration, missing anti-rattle hardware, glazed linings, or worn pads.

A metal tab or sensor that squeals or lights a lamp when the pad nears its wear limit.

Pads worn out so the backing plate contacts the rotor; the rotor is likely damaged.

The hydraulic piston that pushes the pad against the rotor; can seize from corrosion and drag a brake.

On most front calipers, the piston is pushed straight back into its bore to fit new, thicker pads.

Rear calipers with an integrated parking brake usually require the piston to be screwed (turned) in, not pushed.

Clips and shims that keep pads from vibrating; missing hardware causes squeal and uneven wear.

Holds the caliper to the knuckle; pads ride in its abutments, which should be cleaned and lubricated.

The two friction faces must be parallel within spec; non-parallel faces cause thickness variation and pulsation.

A hard, shiny friction surface from overheating that reduces grip and causes squeal.

Oil, grease, or brake fluid on a pad ruins its friction and causes pulling or grabbing; replace the pads.

Grooves cut into the rotor face by worn or embedded pads; machine if within spec, otherwise replace.

Machines a rotor while it's still on the hub to minimize assembled runout.

Machines a removed rotor or drum to true the friction surfaces.

Clips, boots, and pins replaced with pads to keep the caliper sliding and quiet.

A series of moderate stops that transfers an even friction layer to the rotor for quiet, smooth braking.

A rubber seal that keeps dirt and water off the caliper piston and bore.

A square-cut seal that both seals fluid and retracts (rolls back) the piston slightly to release the brake.

Open rotor faces and vents dissipate heat to the air far better than an enclosed drum.

Disc brakes adjust automatically as the piston seal lets the piston follow pad wear.

Felt in the pedal or steering when braking; usually rotor runout or thickness variation.

One wheel runs hot, the car pulls, and fuel economy drops because the brake drags.

Same idea — the rotor must be replaced once it reaches the cast-in minimum/discard thickness.

Contain steel fibers for high heat capacity and fade resistance, but can be noisier and more abrasive.

Produce less dust and noise and are gentle on rotors, with good everyday performance.

Non-asbestos organic pads that are quiet and soft but wear faster and fade sooner under heavy use.

The steel plate the friction material is bonded/riveted to; worn-through pads grind it on the rotor.

Position the bleeder at the top of the caliper so air rises to it during bleeding.

Localized hardened areas from extreme heat that cause thickness variation and pulsation.

Vibration during braking from rotor thickness variation or runout.

Replace pads before the friction material reaches the manufacturer's minimum to protect the rotor.

Rapidly releases and reapplies brake pressure at any wheel about to lock, so tires keep rolling and the driver keeps steering control.

Preventing lockup lets the driver steer while braking hard and stop in a straight line, especially on slippery roads.

Reports each wheel's speed to the ABS module; a wheel slowing much faster than the others signals impending lockup.

A magnet-and-coil sensor that generates AC voltage as a toothed tone ring passes; output rises with speed.

A Hall-effect/magneto-resistive sensor that gives a clean digital signal even at very low speed.

The toothed ring the wheel speed sensor reads; damaged teeth or debris cause erratic signals and ABS codes.

The computer that compares wheel speeds and commands the modulator to prevent lockup.

The ABS valve-and-pump assembly that isolates, dumps, and re-applies pressure at the locking wheel.

Isolation and dump valves inside the modulator that hold, release, and reapply pressure during an ABS event.

Restores pressure to the circuit after the dump valve releases it during an ABS stop.

Normal feedback felt when the modulator cycles rapidly during a hard stop; do not pump the pedal.

The modulator can release and reapply pressure many times per second (about 4–20 Hz) at a locking wheel.

Means the system has set a fault and disabled ABS/TCS/ESC; base hydraulic braking still works.

Even with the ABS lamp on, the normal hydraulic brakes function — only the anti-lock/stability features are off.

Limits wheelspin during acceleration by braking a spinning drive wheel and/or cutting engine power; shares ABS hardware.

Brakes individual wheels and cuts power, using yaw and steering-angle sensors, to correct understeer/oversteer.

Measures the car's rotation about its vertical axis; an ESC input for detecting a skid.

Tells ESC the driver's intended path so it can compare it to the car's actual motion.

Measures side force; an ESC input used with yaw and steering angle to detect loss of control.

The front tires lose grip and the car plows straight; ESC may brake an inside rear wheel to help it turn.

The rear steps out and the car spins; ESC may brake an outside front wheel to straighten it.

Electronic stability control has been required on U.S. light vehicles since the 2012 model year.

Reads ABS/ESC trouble codes and live data and can command the modulator for diagnosis.

A single slow/erratic wheel-speed signal (bad sensor, gap, or tone ring) is a classic ABS fault.

The clearance between sensor and tone ring; too large or full of debris weakens the signal and sets codes.

On start-up the module checks itself and the lamp goes out; a lamp staying on indicates a stored fault.

ABS can lengthen stopping distance on loose gravel or deep snow, where a locked wheel piles material to help stop.

Integrated systems combine the master cylinder/booster with the modulator; non-integrated add the modulator to a conventional system.

Some ABS units require a scan-tool-commanded bleed cycle to purge air from the modulator valves.

Detects a panic stop (fast pedal) and applies maximum boost to shorten stopping distance.

Uses the ABS hardware to balance front-to-rear braking electronically, replacing a mechanical proportioning valve.

Holds brake pressure briefly on an incline so the car doesn't roll back as the driver moves to the accelerator.

ABS works by comparing the four wheel speeds; the slowest-decelerating logic flags impending lockup.

ABS stays dormant and the brakes feel normal; it only activates when a wheel is about to lock.

Lets the driver reduce or disable stability/traction control (e.g., to rock a stuck car); it re-enables at restart.

Both lamps on can mean a serious fault or low fluid affecting EBD — diagnose before driving.

Tone rings are often pressed onto the hub bearing or axle; damage there sets a wheel-speed code.

Corroded or chafed sensor wiring is a common cause of intermittent ABS codes.

Passive (magnetic) sensors lose signal at very low speed; active (Hall) sensors read down to near zero.

A buzz or groan from the modulator during an ABS stop is normal operation, not a failure.