A5: Brakes (Sample Test)

The most likely reason the right-side brake light isn’t working—while all other lights function normally—is a burned-out bulb. Brake lights usually have separate bulbs for each side, so if one fails, only that specific light will stop working. To verify this, you can visually inspect the right-side brake bulb; if the filament appears broken or there’s visible discoloration, the bulb likely needs replacement.

Replacing a brake light bulb is generally a simple task. You’ll need to access the bulb socket, usually by removing a cover or panel behind the light assembly. Refer to your vehicle’s owner’s manual or a repair guide for specific instructions based on your make and model. Once accessed, remove the old bulb, install a new one, and test the brake light to ensure proper operation.

The correct measurement is 14.5 mm. Metric micrometers function similarly to standard micrometers and are compatible in their usage. The sleeve of a metric micrometer displays both whole millimeter and half-millimeter increments—whole numbers on one side and half-millimeter marks on the other. The thimble is divided into 50 increments, each representing 0.01 mm, allowing for very precise readings. To determine a measurement, you read the visible value on the sleeve, add 0.5 mm if a half-millimeter line is present, and then add the thimble reading by multiplying the number of divisions by 0.01 mm. In this case, the combination of readings results in a total of 14.5 mm.

Technician A is correct in stating that sticking slide pins are a common cause of uneven brake pad wear. When slide pins become corroded, dirty, or lose lubrication, they can prevent the caliper from moving freely, leading to one pad wearing more quickly than the other. Technician B is also correct that a sticking caliper piston can result in uneven wear. If the piston fails to retract properly due to corrosion, damage, or contamination from moisture in the brake fluid, it can keep the brake pad pressed against the rotor, accelerating wear on that side.

In addition to these issues, other potential causes of uneven brake pad wear include worn or warped rotors, contaminated or degraded brake fluid, and improper installation of brake pads. All these factors should be inspected during a brake system diagnosis to ensure even pad wear and safe braking performance.

A combination valve is a component used in a vehicle’s braking system that performs multiple critical functions to ensure safe and efficient braking. It combines the following three elements:

Proportioning Valve: Regulates brake fluid pressure between the front and rear brakes to prevent rear-wheel lockup during heavy braking. This helps maintain stability and control.

Metering Valve: Delays the application of the front brakes during light braking, allowing the rear brakes to engage first. This ensures smoother and more balanced braking under normal driving conditions.

Brake Pressure Warning Switch: Monitors hydraulic pressure within the brake system. If it detects a loss of pressure in one circuit, it activates a warning light on the dashboard to alert the driver of a possible brake failure.

The combination valve is typically located near the master cylinder and plays a vital role in overall brake system performance and safety.

Technician A is correct in the proper procedure for adjusting front wheel bearings. The adjusting nut should be tightened to a specified torque while rotating the wheel, then backed off slightly to achieve the correct amount of end play. Once the desired end play is set, a cotter pin is installed to secure the nut in place.

Technician B is incorrect in stating that backing off the castle nut will lead to bearing overheating. Overheating typically results from over-tightening the bearing or applying too much preload, which increases friction and generates excessive heat. Backing off the nut slightly, as part of the proper adjustment process, should not cause overheating if the bearing is properly lubricated and in good condition.

The traction and stability control systems use all of the above input sensors, including the Steering Angle Sensor, Wheel Speed Sensors, and Yaw Rate Sensor.

Steering Angle Sensor: Measures the position and movement of the steering wheel. This helps determine the driver’s intended direction of travel.

Wheel Speed Sensors: Monitor the speed of each individual wheel. This information is used to detect wheel slip and assess the vehicle’s actual speed and direction.

Yaw Rate Sensor: Detects the rate of rotation around the vehicle’s vertical axis. It helps identify understeer and oversteer conditions and assists the system in applying corrective action to maintain stability.

All three sensors are essential for the proper functioning of traction and stability control systems, ensuring the vehicle remains stable and responsive during various driving conditions.

Accumulators are used in both non-integral and integral ABS systems to store hydraulic pressure and ensure quick, responsive braking performance.

• Non-Integral ABS Systems: In these systems, the accumulator is typically located separately from the ABS unit and serves to assist in maintaining brake pressure during ABS operation.

• Integral ABS Systems: Common in modern vehicles, these systems often include high-pressure accumulators built directly into the ABS unit. These accumulators store hydraulic pressure to enable rapid brake actuation when the ABS is engaged.

Technician B is correct in stating that some integral ABS units include high-pressure accumulators that must be drained prior to repair. Releasing this stored pressure is essential to prevent potential injury during maintenance or servicing of the system.

Applying bearing grease to reduce brake squeak is not a correct practice when a ridge has formed on the pads of the backing plate where the brake shoes rest.

• Improper Use of Bearing Grease: Using bearing grease in this area can result in the grease migrating onto the braking surfaces. This can reduce braking effectiveness and cause additional noise or vibration.

• Proper Repair Method: The correct approach is to file or sand the ridges on the backing plate to restore a smooth, flat surface. This ensures proper contact between the brake shoes and the backing plate, which helps improve braking performance and reduces unwanted noise.

• Use of High-Temperature Brake Lubricant: If lubrication is needed, a high-temperature brake-specific lubricant may be used—but only according to the manufacturer’s guidelines. It should not be applied directly to the backing plate where the shoes rest unless specified.

Always follow manufacturer recommendations to ensure proper brake function and safety.

If a new brake rotor is being installed, there is no need to refinish it since it should already have a smooth and even surface.

• New rotors are manufactured with a clean, flat surface that is ready for installation and use. They are designed to meet precise specifications and do not require additional machining.

• Refinishing is typically performed on used rotors to correct surface imperfections such as scoring, warping, or uneven wear. This process restores the rotor’s smooth surface to ensure proper brake pad contact.

Therefore, refinishing is not necessary for new rotors and should only be considered for used ones that show signs of wear or damage.