Brakes A5 Flashcards

Which of the following is caused by a power assist brake booster push rod that is too short?

Answer: Excessive brake pedal travel

If the power assist brake booster push rod is too short, there will be an excessive gap between the push rod and the master cylinder piston when the brake pedal is at rest. This means the brake pedal must travel a greater distance to bridge this gap and begin engaging the master cylinder, resulting in a symptom of excessive brake pedal travel.

Which of the following indicates a spongy brake pedal on a car with 4-wheel disc brakes and a longer than normal travel?

Answer: Air in the hydraulic system

A spongy brake pedal with longer than normal travel is a classic symptom of air trapped within the hydraulic brake system. Unlike incompressible brake fluid, air bubbles compress when the pedal is applied, absorbing some of the pedal force before it can be fully transmitted to the calipers. This compression results in a soft, spongy feel and requires increased pedal travel to achieve effective braking.

A vacuum brake booster is installed on a vehicle. It doesn't have power assist until the engine has been running for a minute, after which it functions normally. What is the most probable cause?

Answer: Defective check valve

The most probable cause is a defective check valve in the vacuum brake booster. The check valve is designed to maintain vacuum within the booster even when the engine is off, providing immediate power assist upon startup. If the check valve is faulty and leaks, the vacuum bleeds off, requiring the engine to run for a period to re-establish sufficient vacuum in the booster before power assist becomes available.

During braking, the brake pedal on a vehicle with power-assisted disc/drum brakes gently glides to the floor. Which of these possibly be the source of the problem?

Answer: An internal master cylinder leak

When the brake pedal gently glides to the floor, it typically indicates an internal leak within the master cylinder. This occurs when the piston seals (cups) are worn or damaged, allowing brake fluid to bypass the piston instead of being forced into the brake lines to actuate the calipers and wheel cylinders. Consequently, hydraulic pressure cannot be maintained, and the pedal slowly loses resistance.

What may be the cause of a spongy brake pedal?

Answer: Air in hydraulic system

A spongy brake pedal is a classic symptom of air trapped within the hydraulic brake system. Unlike brake fluid, which is incompressible, air bubbles compress when the brake pedal is applied. This compression absorbs some of the force intended for the brakes, resulting in a soft, yielding pedal feel and reduced braking efficiency.

The ABS (antilock brake system) amber light does not go off after the engine is started. Technician X says a parking brake not fully released could be the cause. Technician Y says when this happens the brakes will operate like a normal non-ABS brake system. Who is right?

Answer: Y only

Technician Y is correct because when the ABS warning light illuminates, it indicates a fault within the anti-lock braking system, causing it to disable itself. In such cases, the vehicle's brakes will still function, but they will operate as a conventional, non-ABS system, meaning the wheels can lock up under hard braking. Technician X is incorrect; a parking brake not fully released typically illuminates a separate red brake warning light, not the amber ABS warning light.

Even though all of the adjustments have been done according to the specifications, the brake pedal begins to feel spongy and low. What might be the source of the issue?

Answer: Weak hydraulic hose

A weak or deteriorated hydraulic brake hose can cause a spongy and low brake pedal, even after proper adjustments. When brake pressure is applied, a compromised hose can expand or balloon outwards, absorbing some of the hydraulic force instead of fully transmitting it to the brake calipers or wheel cylinders. This expansion results in a soft, spongy pedal feel and increased pedal travel.

When light pedal pressure is applied to a vehicle with disc/drum brakes, the front brakes grab quickly. It's possible that this is the result of a failed:

Answer: metering valve

The metering valve in a disc/drum brake system is designed to slightly delay the application of the front disc brakes. This delay allows the rear drum brake shoes to overcome their return spring tension and make contact with the drums first, ensuring balanced braking. If the metering valve fails or sticks open, the front disc brakes will engage immediately and more aggressively than the rear, causing the front brakes to grab quickly with light pedal pressure.

Which of the conditions listed below can cause brake pedal fade?

Answer: Brake drum machined beyond its limit

Brake pedal fade, characterized by a loss of braking effectiveness, can be caused by a brake drum machined beyond its maximum allowable limit. When a drum is excessively thin, it has less material to absorb and dissipate heat generated during braking. This leads to rapid overheating and distortion of the drum, significantly reducing friction between the shoes and drum, and resulting in severe brake fade.

The axle grease soaked the rear brake linings, and there's still a lot of lining left on them. What is the proper procedure for servicing these brakes?

Answer: Repair leak and replace brake linings

If axle grease has soaked into the rear brake linings, the proper procedure is to repair the source of the leak and replace the brake linings. Grease impregnates the porous friction material, making it impossible to clean effectively and drastically reducing its coefficient of friction. Attempting to clean and reuse contaminated linings would result in severely compromised and unsafe braking performance, necessitating their replacement along with fixing the leak.

The absence of free play on a vehicle's brake pedal can lead to:

Answer: Pressure build-up and dragging brakes

The absence of free play in a vehicle's brake pedal means the master cylinder push rod is constantly applying slight pressure to the piston. This prevents the master cylinder's compensating port from fully opening, which is necessary to relieve residual pressure in the brake lines. Consequently, pressure builds up in the hydraulic system, causing the brakes to drag, overheat, and wear prematurely.

On a car with single piston floating caliper disc brakes, the disc brake pad between the caliper piston and the rotor is badly worn. The other brake pad is slightly worn. Technician X says excessive rotor run out could be the cause. Technician Y says insufficient clearance between the pads and caliper slider could be the cause. Who is right?

Answer: Y only

Technician Y is correct because insufficient clearance between the pads and caliper slider, or seized caliper slide pins, prevents the floating caliper from moving freely. This causes the piston to push only its inner pad against the rotor effectively, while the outer pad receives minimal force, leading to severe wear on the piston-side pad and only slight wear on the outer pad. Technician X is incorrect; excessive rotor runout typically causes brake pulsation and potentially tapered pad wear, but not this specific pattern of uneven wear between the inner and outer pads.

When the front brakes of a car with a drum/disc system are applied lightly, the front brakes lock up. This problem could be caused by a bad:

Answer: Metering valve

In a disc/drum brake system, the metering valve is designed to slightly delay the application of the front disc brakes. This delay allows the rear drum brake shoes to overcome their return springs and make contact with the drums, ensuring balanced braking. If the metering valve is faulty or stuck open, the front disc brakes will engage too quickly and aggressively, causing the front wheels to lock up prematurely, even with light pedal pressure.

All of these steps must be completed when removing the master cylinder, except:

Answer: Drain the master cylinder

Draining the master cylinder completely is not a mandatory step for its removal. While siphoning fluid from the reservoir is often done to minimize spills, the master cylinder itself doesn't need to be fully drained. The other options, such as disconnecting the float level sensor, plugging brake lines to prevent fluid loss and contamination, and relieving vacuum boost pressure, are all essential preparatory steps for safe and clean master cylinder removal.

When the brakes are applied, the front of a car with a disc/drum system vibrates. Which of these possibly be the source of the problem?

Answer: Excessive rotor runout

When the front of a car vibrates during braking, a common cause is excessive rotor runout. Rotor runout, or warp, means the brake rotor is not perfectly flat or concentric. As the brake pads clamp down on this uneven surface, it causes the caliper pistons to move in and out with each rotation, resulting in a noticeable pulsation or vibration felt through the brake pedal and steering wheel.

The race (cup) of a bearing can be dented after it has been shock loaded. What is the type of this sort of bearing failure?

Answer: Brinelling

Brinelling is the specific type of bearing failure characterized by indentations or dents in the bearing race, often caused by static overload or severe shock loading. These permanent depressions occur when the rolling elements are forced into the race material, leaving marks that resemble the hardness test indentations from which the term "Brinell" is derived.

Brakes on an older vehicle with a quick take up valve in the master cylinder are being bled. Technician X believes that you must depress the quick take up valve. Technician Y believes that the brakes can’t be bled. Who is correct?

Answer: Neither technician

A quick take-up valve is an internal master cylinder component designed to rapidly move brake shoes/pads and then reduce fluid volume, not to be manually depressed. Brakes can be bled normally even with this valve present, as its function does not impede the bleeding process. Therefore, both technicians are incorrect in their beliefs.

After machining, the thickness of a front disc brake rotor is slightly less than the minimum thickness specification. The technician should be able to:

Answer: replace the rotor

Disc brake rotors have a critical minimum thickness specification to ensure safe and effective braking. Machining a rotor below this minimum thickness compromises its structural integrity, making it prone to warping, cracking, or overheating, which can lead to brake failure. For safety reasons, any rotor that falls below the minimum thickness after machining must be replaced.

Technician X says a defective wheel or axle bearing can make a growling or rumbling noise. Technician Y says a defective wheel displays looseness or excessive play in the steering wheel especially while driving over rough road surfaces. Who is right?

Answer: Both X and Y

Technician X is correct because a worn or defective wheel or axle bearing commonly produces a growling or rumbling noise, especially noticeable during turns or at certain speeds. Technician Y is also correct; excessive play in a wheel bearing can cause the wheel to move improperly, leading to noticeable looseness or wandering in the steering, particularly over rough road surfaces.

Which of these will be the result of a short power assist brake booster push rod?

Answer: Excessive brake pedal travel

The power assist brake booster push rod connects the brake pedal to the master cylinder. If this rod is too short, it creates excessive free play between the pedal and the master cylinder piston. This means the brake pedal must travel a greater distance before it begins to actuate the master cylinder, resulting in excessive brake pedal travel.