Section 5 DMV Air Brakes (COMPLETED)

What is controlled braking?

-Apply the brakes as hard as you can without locking up the wheels -Keep steering wheel movement minimal -If needed to make larger steering adjustment release the brakes

What is stab braking?

-Apply your brakes all the way -Release the brakes when the wheels lock up -As soon as the wheels start rolling apply your brakes all the way again

Explain a dual air brake system...

-Has 2 separate air brake systems -Operates on a single set of brake controls -One system operates the front axle -One system operates the rear axle -Call "primary" and "secondary" systems

When should you not use the parking brakes?

-If they are very hot -If the brakes are very wet in freezing temperatures

What is a one-way check valve and where is it located?

-This device allows air to flow in one direction only -Located between the air compressor in the first reservoir

Draw an air brake system and its components....

-compressor (In between compressor and tank is one way check valve) -leading to both tanks -second tank to foot pedal (In between tank and foot pedal is the gauge) -from foot pedal to both front and rear brake pods

What is the proper braking technique?

1. Apply the brakes just hard enough to feel a definite slow down 2. When your speed has been reduced to approximately 5 MPH below your safe speed release the brakes.

Steps for low air warning device?

1. Battery on 2. Fan off the pressure by pressing brake pedal repeatedly 3. Low air device should go off no lower than 55 PSI 4. Verbalize what pressure the device went off at 5. Identify the parameters of 55-75 PSI for low alarm

What are 2 reasons that brakes don't work properly?

1. Brake fade 2. Brakes are out of adjustment

DMV BRAKE TEST

1. Chock wheels 2. Start rig build to cut out and shut off 3. Release parking brake 4. Ignition on 5. Static test- 1 minute, not drop more than 2 PSI in 1 minute 6. Applied test- 1 minute, not drop more than 3 PSI in 1 minute 7. Low air alarm test- (visible and audible), 55-75PSI, no lower than 55 8. Spring brake test- bleed brakes, 20-45 PSI 9. Build up test-85-100 PSI in 45 seconds 10. Cut out @ (125 CFD) (120-140 DMV) 11. Compressor cut in test-bleed brakes at no less than 100PSI air should build 12. Parking brake test- brake engaged, put in low gear and pull against brake 13. Service brake test-drive 5 MPH and firmly press on brake pedal

Steps for checking the rate of air pressure buildup?

1. Engine at idle 2. Pressure should build from 85-100 PSI within 45 seconds 3. Verbalize the rate of build

Steps for testing the service brake?

1. Fill tanks 2. Release parking brake 3. Move vehicle forward 5 MPH 4. Apply brakes firmly 5. Look and feel for "pull"

Steps for air leakage rate?

1. Fill the air tanks 2. Turn off the engine 3. Release all brakes 4. Time for 1 minute 5. Verbalize the tanks should not lose more than 2 PSI in 1 minute

How should you check the slack adjusters?

1. Park on level ground chock the wheels 2. Release the parking brake 3. Pull hard on each slack adjuster 4. It's like a just remove more than about 1 inch where the push rod attaches to it, it needs adjustment.

What are the 4 different factors that play a part in stopping distance?

1. Perception distance 2. Reaction distance 3. Brake lag distance 4. Braking distance = total stopping distance

Steps for the spring brake test?

1. Release the parking brake 2. Fan off the pressure 3. Brake should engage at 20-45 PSI 4. Verbalize when the brake popped

Steps for testing the parking brake? SEATBELT

1. SEATBELT 2. Set the parking brake 3. Pull against brake in low gear

Air brakes are really three different braking systems, what are they?

1. Service brake system 2. Parking brake system 3. Emergency brake system

Steps for the Applied Leakage Test (1 minute hold)?

1. Start the engine and build pressure to cut out pressure 2. Identify when compressor cuts out 3. Shut off engine 4. Chock tires 5. Apply pressure to brake pedal hold for 1 minute 6. Let needle settle 7. Verbalize no more than 3 PSI in 1 minute 8. Listen for air leaks

What is S-cam brakes?

1.When you push the brake pedal, air is let into each brake chamber 2. Air pressure then pushes the rod out 3. Moving the slack adjuster thus twisting the brake camshaft 4. This turns the S cam 5. S-cam forces the brake shoes away from one another and presses them against the inside of the brake drum 6. When you release the brake pedal the S-cam then rotates back and a spring pulls the brake shoes away from the drum letting the wheel freely spin again.

Before driving a vehicle with a dual air system what should the pressure in both air tanks be?

100 PSI

What is the cut in pressure? (When the compressor turns on)

100 PSI

What is the cut out pressure? (When the compressor shuts off)

125 PSI

What psi does a safety relief valve open on a air tank?

150 PSI

Total braking distance for vehicle traveling 25 MPH?

155'

What is the range for spring brakes to be engaged?

20-45 PSI

Total braking distance for vehicle traveling 35 MPH?

243'

What is the air brake lag distance at 55 MPH on dry pavement?

32 feet

Total braking distance for vehicle traveling 45 MPH?

346'

Total braking distance for vehicle traveling 55 MPH?

451'

If air pressure drops to below the low air PSI what PSI will the low warning air go off?

55 PSI

What is the range for the LOW AIR PRESSURE warning to come on?

55-75 PSI

Total braking distance for vehicle traveling 15 MPH?

81'

A full service brake application must deliver to all brake chambers no less than what % of the air pressure remaining with the brakes fully applied?

90%

If a slack adjuster moves how much where the push rod attaches to it then it probably needs adjustment?

About 1 inch

What is an air compressor and how does it work?

Air compressor pumps air into the air reservoirs. The compressor is connected to the engine through gears. The compressor may be air cooled or cooled by the engine cooling system and may have its own oil supply or be lubricated by the engine oil.

What is an air tank drain and how does it work?

Air tanks usually have some water and compressor oil in it which is bad for the brake system, These fluids can be drained with a drain valve in the bottom of the tank.

What is a spring brake?

All trucks, truck tractors and buses must be equipped with emergency brakes and parking brakes. They must be held on by mechanical force (because air pressure can leak). Spring brakes are used to meet these. Powerful springs are held back by air pressure when driving if the air pressure is removed the springs put on the brakes.

What is the service brake system?

Applies and releases the brakes when you use the brake pedal during normal driving

What is the parking brake system?

Applies and releases the parking brakes when you use the parking brake control

What psi is the low air pressure warning alarm activated?

Between 55-75 PSI or 1/2 the compressor governor cut out pressure

Explain brake drums shoes and linings and how they operate?

Brake drums are located on each end of the vehicles axles the wheels are bolted to the drums and the braking mechanism is inside the drum. When pedal is applied the brake shoes and linings are pushed against the inside of the drum this causes friction was which slows the vehicle.

How do you know if your vehicle is equipped with anti-lock brakes?

Check the certification label for the date of manufacture to determine if your vehicle is equipped with ABS.

What do air brakes use to make the brakes work?

Compressed air

Why must air tanks be drained?

Compressed air usually has some water and some compressor oil in it which is bad for the brake system the water and oil tend to collect in the bottom of the air tank.

If your vehicle doesn't have automatic air tank drains when should you drain the tanks?

Drain the tanks at the end of each working day

When should the manual adjustment of an automatic adjuster be used?

For temporary measure to correct the adjustment in an emergency situation.

What does ABS do?

Helps you avoid wheel lock up, computer senses impending lock up, reduces the breaking pressure to a safe level and helps you maintain control.

When the automatic slack adjuster needs adjustment what is the recommendation?

It is recommended that when brakes equipped with automatic adjusters are found to be out of adjustment the driver takes the vehicle to a repair facility as soon as possible.

Linings must not be worn dangerously thin which is?

Less than 1/4 inch

Brake drums must not have cracks longer than what?

Longer than 1/2 the width of the friction area

What are the two types of air tank drains?

Manual and automatic Manual-Operated by turning a quarter turn or pulling a Cable Automatic-The water and oil are automatically expelled

Should automatic slack adjusters be manually adjusted?

No, If the adjusters exceed the limit of movement it is usually an indication of a mechanical problem.

What type of brakes are slack adjusters found on?

S-cam brakes

What is a safety valve pertaining to an air tank?

Safety relief valve installed in the first tank the air compressor pumps to, The safety valve protect the tank and the rest of the system from too much pressure. The valve is usually set to open at 150 psi.

What are spring breaks?

Spring breaks must be held on by mechanical force (because air pressure can eventually leak away) spring breaks meet those needs. Powerful springs are held back by air pressure when driving, if the pressure is removed the springs put on the brakes.

If you are driving and the warning light and buzzer for low air comes on what should you do?

Stop right away and safely park the vehicle.

What is an air governor and how does it work?

The governor controls when the air compressor will pump air into the air storage tanks. When the air tank pressure rises to the cut out level around 125 psi the governor stops the compressor from pumping air. When the tank pressure falls to the cut in pressure around 100 psi the governor allows the compressor to start pumping again.

What is the "wigwag" warning?

The wigwag warning is a mechanical arm that is put into your view when the pressure is between 55 and 75 psi.

What PSI does the spring brake engage?

They will fully come on when air pressure drops to 20-45 PSI

What is the supply (application) pressure gauge used for?

This gauge shows how much air pressure you are applying to the brakes, increasing application pressure to hold the same speed means the brakes are fading.

What is "brake lag"?

This is the time required for the brakes to work after the brake pedal is pushed.

All vehicles with airbrakes must have a low air pressure warning signal true or false?

True

What is the emergency brake system?

Uses Parts of the system and parking brake systems to stop the vehicle in a brake system failure

Are front wheel brakes good under all conditions?

Yes

Do we check automatic slack adjusters?

Yes, even though they are "automatic" they still need to be checked