Disc Brakes MCFRS Driver Certification Module

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.

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.