Disc Brakes MCFRS Driver Certification Module

Questions and Answers

What mechanism is used in air-operated disc brakes to create clamping pressure on the disc?

Hydraulic Cylinder

Piston Mechanism

S-cam system

Power Screw (correct)

What is the required action before the low air pressure warning signal activates?

Pressure in air tanks falls below 60 psi (correct)

Pressure in air tanks falls below 40 psi

Pressure in air tanks falls below 80 psi

Pressure in air tanks rises above 60 psi

How are the emergency and parking brakes on vehicles held in place?

By electrical energy

By hydraulic force

By pneumatic controls

By mechanical force (correct)

What happens to the spring brakes if air pressure is lost during driving?

They automatically apply the brakes Signup and view all the answers

How do vehicles notify drivers behind them that the brakes are being applied?

With an electric switch activated by air pressure Signup and view all the answers

What is typically used to adjust the parking brake in most vehicles?

A diamond-shaped, yellow, pull-push control knob Signup and view all the answers

In a dual air brake system, how is air pressure monitored?

By individual gauges for each half of the system Signup and view all the answers

What is the primary function of the supply pressure gauge in an air-brake system?

To indicate the pressure in the air tanks Signup and view all the answers

What is the primary role of the differential in the rear axle system?

To allow wheels on the same axle to rotate at different speeds during turns. Signup and view all the answers

When should the locking differential be engaged for optimal performance?

When the vehicle is freely moving. Signup and view all the answers

Which statement best describes the function of the Inter-Axle Differential Lock (IAD)?

It compensates for differences in speed between the two axles. Signup and view all the answers

What must be avoided when using the IAD lock with rear wheels spinning?

Engaging the lock at highway speeds. Signup and view all the answers

What distinguishes a standard transmission from an automatic transmission?

Automatic transmission is controlled by computer modules during shifting. Signup and view all the answers

What is required for wheels and tires in terms of weight management?

They need to have a weight rating that accommodates the axle's load. Signup and view all the answers

What is the primary function of the electrical system in a vehicle?

To supply power for vital and auxiliary functions. Signup and view all the answers

Which of the following is NOT a component of the steering system?

Clutch assembly. Signup and view all the answers

What happens when a vehicle drives on dry pavement with the locking differential engaged?

It risks damaging tires or axle components. Signup and view all the answers

What is the purpose of the suspension system in a vehicle?

To provide comfort and control on rough terrain and curves. Signup and view all the answers

What is the minimum recommended tread depth specifically for emergency vehicles?

4/32 inches Signup and view all the answers

Which inspection category includes checking the cleanliness and body damage of the vehicle?

Vehicle overview Signup and view all the answers

Automatic traction control primarily assists in maintaining traction by doing what?

Automatically applying brakes to spinning drive wheels Signup and view all the answers

What should be the driver’s first action before conducting an interior cab inspection?

Engage the parking brake and chock the wheels Signup and view all the answers

Which fluid levels are checked during the engine compartment inspection?

All of the above Signup and view all the answers

What must the driver confirm about the vehicle before it is deemed ready for use?

It is mechanically safe for operation Signup and view all the answers

When traction is lost and automatic traction control is limiting acceleration, what should the driver do?

Engage the 'mud and snow' switch Signup and view all the answers

During the preventive maintenance inspection process, which step involves reviewing past defects?

Checking prior maintenance records Signup and view all the answers

Which of the following checks is crucial for assessing potential leaks in the vehicle?

Listening for leaks during the brake test Signup and view all the answers

What is a primary responsibility of the driver regarding vehicle maintenance?

Confirm the vehicle is ready for use Signup and view all the answers

What function does the hydraulic type of driveline retarder serve?

Absorbs energy by pumping oil Signup and view all the answers

Why should the retarder be turned off during inclement weather?

It can lead to loss of traction Signup and view all the answers

What is the main purpose of Diesel Exhaust Fluid (DEF) in post-2009 diesel vehicles?

To break down nitrogen oxide emissions Signup and view all the answers

What should be avoided to prevent crystallization of Diesel Exhaust Fluid (DEF)?

Storing opened containers for prolonged periods Signup and view all the answers

What happens when the Diesel Exhaust Fluid (DEF) tank reaches empty?

The vehicle automatically reduces power Signup and view all the answers

What is the primary concern associated with a faulty exhaust system?

Poisonous fumes entering the crew area Signup and view all the answers

How does the Diesel Particulate Filter (DPF) indicate when regeneration is necessary?

By illuminating an indicator light Signup and view all the answers

What is the typical freezing point of Diesel Exhaust Fluid (DEF)?

12°F Signup and view all the answers

Which component of the driveline is NOT directly involved in the function of the retarder?

Differential Signup and view all the answers

What material is used in Diesel Exhaust Fluid (DEF)?

32.5% urea and 67.5% de-ionized water Signup and view all the answers

What is the minimum tread depth required on non-steering axles?

2/32" Signup and view all the answers

Which system should be checked to ensure the vehicle can maintain electrical systems at fast idle RPMs?

Fast idle RPMs Signup and view all the answers

During a vehicle walk around, which of the following should be checked specifically for potential vision obstruction?

Windshield Signup and view all the answers

Which part should not have excessive movement more than 1 inch and should be checked during a brake system inspection?

Slack adjusters Signup and view all the answers

What must be checked for any obvious fluid leaks during an undercarriage inspection?

Air tanks Signup and view all the answers

Which warning devices are required to be on board as part of DOT regulations?

Reflective triangles, cones, and flares Signup and view all the answers

What condition indicates the need for bleeding moisture from the air tanks?

Light gray sludge Signup and view all the answers

What should be checked on tires in addition to inflation and tread depth?

Presence of gouges or cuts Signup and view all the answers

Which of the following is not a component to check in the interior lighting system?

Headlight function Signup and view all the answers

Which document is not typically checked during a vehicle inspection?

Driver's social security card Signup and view all the answers

What is the primary function of the Antilock Braking System (ABS)?

To maintain full control while stopping Signup and view all the answers

In a dual air brake system, what does the primary system typically operate?

Rear axle brakes Signup and view all the answers

Which type of auxiliary brake is also known as a compression brake?

Engine Brake Signup and view all the answers

What is the purpose of the driveline brake in a parking brake system?

To prevent the vehicle from rolling when parked Signup and view all the answers

Why is it advised not to push the brake pedal down when the spring brakes are on?

It could damage the brake system Signup and view all the answers

Which component is part of the automatic transmission retarder system?

Vaned rotor Signup and view all the answers

When is the engine brake typically not effective on vehicles with automatic transmission?

Below 20 miles per hour Signup and view all the answers

What happens when the ABS senses that a wheel is about to lock up?

It pumps the brakes on that wheel Signup and view all the answers

What condition should the engine brake's mode be set during inclement weather?

Off or lower mode Signup and view all the answers

How many separate air brake systems are typically found in a dual air brake system?

Two Signup and view all the answers

Study Notes

Disc Brakes

Air-operated disc brakes utilize air pressure to actuate a power screw, pressing a caliper against brake lining pads, functioning like a large C-clamp.
The system includes slack adjusters akin to S-cam brakes.

Air Brake System Components

Supply Pressure Gauge: Displays pressure in tanks; dual systems have separate gauges or a dual needle gauge.
Low Air Pressure Warning: Activates a visible signal (usually a red light) before pressure drops below 60 psi.
Brake Light Switch: Turns on brake lights automatically upon brake application, activated by air pressure.

Spring Brakes

Essential for emergency and parking; they apply automatically when air pressure is lost.
Engaged by mechanical force, preventing reliance on air pressure alone.

Parking Brake Controls

Typically a yellow, diamond-shaped knob used to engage or release spring brakes.
Best practice avoids pressing the brake pedal when spring brakes are engaged to prevent damage.

Dual Air Brake System

Consists of two separate systems (primary for rear and secondary for front axles) enhancing safety.
Common in newer vehicles for redundancy; allows for continued braking even if one system fails.

Antilock Braking Systems (ABS)

Prevents wheel lock-up during braking, maintaining steering control and stability.
Sensors detect wheel speed; the system automatically "pumps" brakes to prevent wheels from locking.

Auxiliary Braking Systems

Engine Brake: Also known as compression brake; utilizes engine compression to slow the vehicle.
Automatic Transmission Retarder: Attached to the transmission, it uses pressurized fluid interaction to decelerate the vehicle.
Driveline Retarder: Can be hydraulic or electromagnetic, absorbing energy to slow the vehicle.

Exhaust Systems

Modern diesel engines are fitted with "aftertreatment" systems that include Diesel Exhaust Fluid (DEF) and Diesel Particulate Filter (DPF).
DEF reduces nitrogen oxide emissions; it's stored separately and should be replenished before empty to avoid power reduction.

Driveline Components

Comprises transmission, driveshafts, and differential, allowing for varying wheel speed during turns.
Locking differential ensures equal torque distribution to wheels; should only engage below 25 mph.

Steering System

Steering is controlled through a mechanism connecting the steering wheel and column to front wheels, often enhanced with power assist for easier maneuverability.

Electrical Systems

Powers essential vehicle functions like lights, horn, siren, and public address systems as well as the primary electrical components.

Suspension System

Includes leaf springs, shock absorbers, and tire systems to maintain vehicle control over rough terrain.

Wheels and Tires

Must meet weight ratings and display proper inflation and tread conditions; minimum recommended tread depth for emergency vehicles is 4/32 inches.
Automatic traction control systems aid tire traction by selectively applying brakes to spinning wheels.

Preventive Inspections for Emergency Vehicles

Regular inspections are vital to maintain vehicle readiness and prevent accidents caused by mechanical failures.
Inspections cover nine core areas, including maintenance records, engine checks, interior controls, walk-around assessments, and emergency systems.

Inspection Categories Explained

Check PM Records: Review previous maintenance logs for issues.
Vehicle Overview: Assess for damage and cleanliness; check for vehicle leveling.
Engine Compartment Check: Verify oil, fluid, and battery levels; inspect belts and seals.
Interior Cab Check: Test instrumentation, brake functionality, steering, and communication systems.
Vehicle Walk Around: Inspect tires, lights, and external features for operational integrity.
Undercarriage Check: Assess condition of the underside, including brake lines.

Overall Vehicle Safety Responsibility

The driver is responsible for mechanical safety and must ensure the vehicle is fit for duty; "if it isn't right, do not drive it."### Tread Depth Requirements
Steering axles require a minimum tread depth of 4/32”.
Non-steering axles require a minimum tread depth of 2/32”.

Snow Chains and Fluid Leaks

Automatic snow chains must be assessed for condition, positioning, and operational status.
Check undercarriage and ground for fluid leaks, noting the fluid's color for diagnosis.

Compartment and Equipment Checks

Ensure compartment latching mechanisms function correctly.
Verify portable power equipment is operational and adequately fueled.
Confirm inventory is complete and items are stored in designated locations.
Inspect circuit breakers on onboard generators for functionality.
Check that DOT-required traffic warning devices (cones, flares, reflective triangles) are present.
Ensure at least one dry chemical fire extinguisher is available and fully charged.

Crew Equipment Verification

Basic crew equipment should include SCBA, handheld lights, AED, and EMS supplies.
All crew equipment must be checked for operational integrity.
Additional equipment, such as haz-mat lights, should also be functioning properly.

Undercarriage Inspection

Regularly bleed moisture from air tanks to prevent damage.
Light gray sludge in fluids indicates compressor issues.
Brake lines should be examined for cracks, fraying, dry rot, or excessive wear.
Slack adjusters should show no more than 1 inch of excessive movement; adjustments should not be attempted without trained personnel.
Ensure proper greasing of the driveline; check joints for excessive movement and intact dust covers.
Inspect the exhaust system for soot stains that may indicate leaks, as well as checking clamps.

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Description

Explore the mechanics of air-operated disc brakes as part of the MCFRS Driver Certification Program. This quiz covers vital components such as the power screw and the role of air pressure in the braking system, along with comparisons to traditional S-cam brakes. Understand these essential concepts to enhance your knowledge in vehicle technology.