Podcast
Questions and Answers
You should know that your brakes are fading when?
You should know that your brakes are fading when?
You have to push harder on the brake pedal to control your downhill speed.
If the spring brakes are on when should you push the brake pedal?
If the spring brakes are on when should you push the brake pedal?
Never
Repeatedly pressing and releasing (fanning) the brake pedal may result in?
Repeatedly pressing and releasing (fanning) the brake pedal may result in?
A loss of air pressure.
The driver must be able to see a low air pressure warning which comes on before pressure in the service air tank falls below ______ PSI.
The driver must be able to see a low air pressure warning which comes on before pressure in the service air tank falls below ______ PSI.
If your truck or bus has dual parking control valves you can use pressure from a separate tank?
If your truck or bus has dual parking control valves you can use pressure from a separate tank?
The brake pedal in the air brake system?
The brake pedal in the air brake system?
To check the free play of manual slack adjusters of S-Cam brakes, you should?
To check the free play of manual slack adjusters of S-Cam brakes, you should?
Parking or emergency brakes on trucks or buses can be legally held on by ___________ pressure.
Parking or emergency brakes on trucks or buses can be legally held on by ___________ pressure.
Emergency stab braking is when you?
Emergency stab braking is when you?
The most common type of foundation brakes found on heavy vehicles is the?
The most common type of foundation brakes found on heavy vehicles is the?
If your truck has a dual air brake system and one of the systems is low on pressure?
If your truck has a dual air brake system and one of the systems is low on pressure?
The most important thing to do when a low pressure warning light comes on is to?
The most important thing to do when a low pressure warning light comes on is to?
With air brake equipped vehicles, the parking brakes should be used?
With air brake equipped vehicles, the parking brakes should be used?
The air compressor governor controls?
The air compressor governor controls?
The stop light switch?
The stop light switch?
For air brake systems in good condition the air compressor should start pumping at about ______ PSI.
For air brake systems in good condition the air compressor should start pumping at about ______ PSI.
The air loss rate for a straight truck or bus with the engine off and the parking brakes off and the service brakes on should not be more than?
The air loss rate for a straight truck or bus with the engine off and the parking brakes off and the service brakes on should not be more than?
The braking power of the spring brakes?
The braking power of the spring brakes?
How should you check spring brakes application when air pressure drops below a certain level?
How should you check spring brakes application when air pressure drops below a certain level?
If you are driving down a steep grade and have reached a safe speed of 40 MPH you would apply the service brakes until your speed drops to _____ MPH.
If you are driving down a steep grade and have reached a safe speed of 40 MPH you would apply the service brakes until your speed drops to _____ MPH.
Air brake lag distance at 55 MPH adds about _____ feet to your stopping distance.
Air brake lag distance at 55 MPH adds about _____ feet to your stopping distance.
How should you check that your service brakes are working properly?
How should you check that your service brakes are working properly?
Emergency controlled braking is when you?
Emergency controlled braking is when you?
Which of these is not a proper time to apply the parking brake?
Which of these is not a proper time to apply the parking brake?
All air brake equipped vehicles have?
All air brake equipped vehicles have?
If air pressure does not build up to normal within the correct amount of time then?
If air pressure does not build up to normal within the correct amount of time then?
Excessive use of the service brakes results in overheating which can lead to?
Excessive use of the service brakes results in overheating which can lead to?
The proper method of braking when going down a long and/or steep grade, after selecting the proper gear is to brake until your speed is about _____ MPH below your 'safe' speed then release your brakes.
The proper method of braking when going down a long and/or steep grade, after selecting the proper gear is to brake until your speed is about _____ MPH below your 'safe' speed then release your brakes.
Under normal conditions in order to engage the parking brakes the driver must first?
Under normal conditions in order to engage the parking brakes the driver must first?
Total stopping distance for air brakes is longer than for hydraulic brakes due to?
Total stopping distance for air brakes is longer than for hydraulic brakes due to?
If you must make an emergency stop you should brake so you?
If you must make an emergency stop you should brake so you?
The parking or emergency brakes on a heavy vehicle can only be held in position by something that cannot leak away like?
The parking or emergency brakes on a heavy vehicle can only be held in position by something that cannot leak away like?
Some air brake systems have an alcohol evaporator, what may happen if you don't keep the unit filled?
Some air brake systems have an alcohol evaporator, what may happen if you don't keep the unit filled?
The brake system that applies and releases the brakes when the driver uses the brake pedal is the __________ brake system.
The brake system that applies and releases the brakes when the driver uses the brake pedal is the __________ brake system.
Before driving a truck or bus with a dual air brake system the pressure in each system should be at least _________ PSI.
Before driving a truck or bus with a dual air brake system the pressure in each system should be at least _________ PSI.
Your truck or bus has a dual air brake system, if a low air pressure warning comes on for only one system what should you do?
Your truck or bus has a dual air brake system, if a low air pressure warning comes on for only one system what should you do?
What happens when your brake drums get very hot?
What happens when your brake drums get very hot?
How often should the air tanks be drained?
How often should the air tanks be drained?
An air application gauge shows?
An air application gauge shows?
The difference between controlled braking and stab braking is?
The difference between controlled braking and stab braking is?
Front brake limiting valves reduce the air pressure applied to the front brakes by?
Front brake limiting valves reduce the air pressure applied to the front brakes by?
To charge/release the brakes with air you must?
To charge/release the brakes with air you must?
The tractor air supply valve is what color?
The tractor air supply valve is what color?
When the engine is at operating RPM the pressure should build up to 85 to 100 PSI within ______ seconds in dual air systems.
When the engine is at operating RPM the pressure should build up to 85 to 100 PSI within ______ seconds in dual air systems.
Brake drums must not have cracks longer than ______ the width of the friction area.
Brake drums must not have cracks longer than ______ the width of the friction area.
In single air systems (pre 1975) air pressure should build from 50-90 PSI within _____ minutes.
In single air systems (pre 1975) air pressure should build from 50-90 PSI within _____ minutes.
In air operated disc brakes air pressure acts on a brake chamber and slack adjuster like S-Cam brakes but instead of the S-Cam a _______ is used.
In air operated disc brakes air pressure acts on a brake chamber and slack adjuster like S-Cam brakes but instead of the S-Cam a _______ is used.
A safety relief valve is used to protect the air system from too much air pressure. This valve is usually set to open at ______PSI.
A safety relief valve is used to protect the air system from too much air pressure. This valve is usually set to open at ______PSI.
Tractor and straight truck spring brakes will apply fully when air pressure drops to a range of _____ PSI.
Tractor and straight truck spring brakes will apply fully when air pressure drops to a range of _____ PSI.
On large buses it is common for the low pressure warning device to signal at _____ PSI.
On large buses it is common for the low pressure warning device to signal at _____ PSI.
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Study Notes
Air Brakes Overview
- Brake fading occurs when more force is needed on the brake pedal to manage downhill speeds.
- Spring brakes should never be engaged while pressing the brake pedal.
- Fanning the brake pedal can lead to a loss of air pressure.
Air Pressure Monitoring
- A low air pressure warning activates before falling below 60 PSI.
- Brake systems may be compromised if one part of a dual air brake system is low on pressure.
Brake Functionality
- The brake pedal regulates air pressure for braking.
- Parking or emergency brakes in heavy vehicles rely on spring pressure.
- Service brakes must be adjusted for spring brakes to function effectively.
Brake Testing and Maintenance
- Check slack adjusters by parking on level ground and manipulating the adjusters.
- Air tanks must be drained daily to prevent water buildup and ensure functionality.
- Inspect brake drums for any cracks exceeding half the friction area width.
Emergency Procedures and Braking Techniques
- Emergency stab braking involves applying full brake pressure, releasing when wheels lock, and re-applying when they begin rolling.
- Controlled braking allows for steering without wheel lock-up.
- The safest speed to resume brakes after descending a steep grade is 35 MPH.
Brake Characteristics
- Air brake systems generally have a longer stopping distance than hydraulic brakes due to brake lag.
- The air compressor typically starts pumping air into the tanks at around 100 PSI.
- Total stopping distance includes air brake lag which adds roughly 32 feet at 55 MPH.
Operational Protocols
- Use parking brakes whenever the vehicle is parked.
- If air pressure does not build to normal quickly, it can necessitate an emergency stop.
- A supply air pressure gauge is standard on all air brake-equipped vehicles.
Warnings and Indicators
- The stop light switch alerts surrounding drivers when brakes are applied.
- Low pressure warnings prompt immediate safe parking.
- Low pressure warnings in dual systems require immediate attention.
Additional Components
- Power screws replace S-Cams in air-operated disc brakes.
- Excessive use of service brakes can cause overheating and drum expansion.
- The tractor air supply valve is identifiable by its yellow color.
General Best Practices
- Maintain proper brake function by checking service brakes through controlled movements.
- Ensure that alcohol evaporators are filled to avoid ice formation in air lines.
- Front brake limiting valves decrease pressure by half to maintain control.
Contextual Facts
- The air loss rate for straight trucks should not exceed 3 PSI in one minute when the engine is off and brakes are applied.
- The pressure in dual air brake systems should equal at least 100 PSI before operation.
- Emergency brake systems are designed to retain pressure without leaks, utilizing spring pressure for safety.
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