10 Air Brake Operations

Question 1

Air brakes are able to generate ___________________ than hydraulic brakes.

Answer 1

more stopping power

Question 2

Downside of air brakes:

Answer 2

Lag time (time it takes to pressurize brake system)

Question 3

Air brake chambers are divided into two sides:

Answer 3

Service brakes (brake petal)
Spring brakes (parking brake)

Question 4

The spring brake acts as a failsafe in the event of an air leak.

Answer 4

Instead of losing the brake system, the spring brake will engage and stop the truck.

Question 5

Drum brake system: Stroke

Answer 5

The distance the pushrod has to travel to properly apply the brake.

Question 6

Parking brake knob should pop out when the air pressure reaches ________.

Answer 6

20-40 psi

Question 7

Three reasons why commercial braking efficiency is worse than passenger vehicles:

Answer 7

1. Rubber composition of truck tires
2. Lag time of brake system
3. Brake fade

Question 8

FDs who should be especially wary of brake fade:

Answer 8

1. Districts with hills
2. Long distance responses
3. Stop-and-go traffic

Question 9

Mechanical Fade - Drum brakes

Answer 9

Overweight or speeding vehicles will create more kinetic energy. As a result of the excess kinetic energy, the brakes may overheat and start to fade.

Question 10

Crack pressure

Answer 10

Amount of air needed to open the valve

Question 11

As the pushrod stroke grows longer, __________________ is applied to the wheel.

Answer 11

Less braking force

Question 12

And ideal brake adjustment will result in no more than a 90-degree angle between the pushrod and the slack adjuster.

Question 13

Downshifting

Answer 13

Use of the vehicles transmission to slow the vehicle

Question 14

Each piston in a diesel engine is performing one of four functions:

Answer 14

1. Induction
2. Compression
3. Power
4. Exhaust

Question 15

Auxiliary Braking Devices

Answer 15

1. Compression Release Engine Retarder
2. Exhaust Retarder
3. Electro-magnetic Retarder
4. Transmission Retarder

Question 16

Different ways to activate brake retarders

Answer 16

1. When foot comes off the throttle
2. When brake pedal is depressed
3. Separate hand control for manual activation

Question 17

Snub breaking

Answer 17

• The recommended method of braking when descending a long grade
• Produce same amount of heat as long, soft application of the brakes

Question 18

Recommended practice for snub braking:

Answer 18

1. Apply brakes hard enough to feel a slowdown in the vehicle
2. When speed is reduced to 5 mph below safe speed, release brakes
3. When speed has increased to a safe speed, repeat steps 1 and 2

Question 19

Vehicle NOT equipped with ABS:

Answer 19

Threshold braking

Question 20

Vehicle equipped with ABS:

Answer 20

Stomp, Stay, Steer