Michigan CDL Air Brakes UPDATED
ACTUAL Exam Questions and CORRECT
Answers
3 different braking systems that make up Air Brakes - CORRECT ANSWER - Service
Brake, Parking Brake, Emergency Brake
Air Compressor - CORRECT ANSWER - Pumps air into storage tanks and connected to
the engine via gears or a v-belt.
Air Compressor Governor - CORRECT ANSWER - Controls when the air compressor
will pump air into the air storage tanks. When tank pressure rises to the cut-out level, the
governor stops the compressor from pumping. When the tank pressure falls to the cut-in level,
the governor allow the compressor to pump again.
Cut-Out Level - CORRECT ANSWER - 125 PSI (Governor stops the compressor from
pumping air)
Cut-In Level - CORRECT ANSWER - 100 PSI (Governor allows compressor to start
pumping again)
Air Storage Tanks - CORRECT ANSWER - Holds the compressed air.
Air Tank Drains - CORRECT ANSWER - Valve to drain oil and water from the tanks.
Alcohol Evaporator - CORRECT ANSWER - Puts alcohol into the air system to reduce
risk of ice in the valves.
Safety Valve - CORRECT ANSWER - In the first take air is pumped in to...protects the
tank and system from too much pressure. Set to open at 150 PSI.
, Foundation Brakes - CORRECT ANSWER - Used at each wheel...most common type is
the S-Cam drum brake.
Drums, Shoes and Linings - CORRECT ANSWER - Drums located on each end of the
axles. Wheels are bolted to the drums. To stop, the brake shoes and linings are pushed against the
inside of the drum.
S-Cam Brakes - CORRECT ANSWER - Pressure pushes the rod out, moving the slack
adjuster, thus twisting the brake camshaft. Forces the brake shoes away from one another and
presses them against the inside of the brake drum.
Supply Pressure Gauges - CORRECT ANSWER - Tells you how much pressure is in the
air tanks. Will be one for each half the the brake system in dual air brake systems.
Application Pressure Gauge - CORRECT ANSWER - Shows how much pressure you are
applying to brakes. (Not on all vehicles). Increasing pressure to hold same speed means brakes
are fading. Slow down and use lower gear.
Causes for increased pressure: - CORRECT ANSWER - Brakes out of adjustment, Air
leaks, Mechanical problems
Low Air Pressure Warning - CORRECT ANSWER - Required on all vehicles with air
brakes. Signal that must come on before the pressure in tanks falls below 60 PSI.
Spring Brakes - CORRECT ANSWER - Used for emergency brakes and parking brakes.
Held back by air pressure. If pressure removed, the springs put on the brakes. In tractors and
straight trucks, these will come on when air pressure drops to 20 - 45 PSI (typically 20 - 30 PSI).
Dual Air Brakes - CORRECT ANSWER - Has two separate air brake systems (Primary
and Secondary), which use a single set of brake controls. Each has its own tanks, hoses, lines,
etc.
ACTUAL Exam Questions and CORRECT
Answers
3 different braking systems that make up Air Brakes - CORRECT ANSWER - Service
Brake, Parking Brake, Emergency Brake
Air Compressor - CORRECT ANSWER - Pumps air into storage tanks and connected to
the engine via gears or a v-belt.
Air Compressor Governor - CORRECT ANSWER - Controls when the air compressor
will pump air into the air storage tanks. When tank pressure rises to the cut-out level, the
governor stops the compressor from pumping. When the tank pressure falls to the cut-in level,
the governor allow the compressor to pump again.
Cut-Out Level - CORRECT ANSWER - 125 PSI (Governor stops the compressor from
pumping air)
Cut-In Level - CORRECT ANSWER - 100 PSI (Governor allows compressor to start
pumping again)
Air Storage Tanks - CORRECT ANSWER - Holds the compressed air.
Air Tank Drains - CORRECT ANSWER - Valve to drain oil and water from the tanks.
Alcohol Evaporator - CORRECT ANSWER - Puts alcohol into the air system to reduce
risk of ice in the valves.
Safety Valve - CORRECT ANSWER - In the first take air is pumped in to...protects the
tank and system from too much pressure. Set to open at 150 PSI.
, Foundation Brakes - CORRECT ANSWER - Used at each wheel...most common type is
the S-Cam drum brake.
Drums, Shoes and Linings - CORRECT ANSWER - Drums located on each end of the
axles. Wheels are bolted to the drums. To stop, the brake shoes and linings are pushed against the
inside of the drum.
S-Cam Brakes - CORRECT ANSWER - Pressure pushes the rod out, moving the slack
adjuster, thus twisting the brake camshaft. Forces the brake shoes away from one another and
presses them against the inside of the brake drum.
Supply Pressure Gauges - CORRECT ANSWER - Tells you how much pressure is in the
air tanks. Will be one for each half the the brake system in dual air brake systems.
Application Pressure Gauge - CORRECT ANSWER - Shows how much pressure you are
applying to brakes. (Not on all vehicles). Increasing pressure to hold same speed means brakes
are fading. Slow down and use lower gear.
Causes for increased pressure: - CORRECT ANSWER - Brakes out of adjustment, Air
leaks, Mechanical problems
Low Air Pressure Warning - CORRECT ANSWER - Required on all vehicles with air
brakes. Signal that must come on before the pressure in tanks falls below 60 PSI.
Spring Brakes - CORRECT ANSWER - Used for emergency brakes and parking brakes.
Held back by air pressure. If pressure removed, the springs put on the brakes. In tractors and
straight trucks, these will come on when air pressure drops to 20 - 45 PSI (typically 20 - 30 PSI).
Dual Air Brakes - CORRECT ANSWER - Has two separate air brake systems (Primary
and Secondary), which use a single set of brake controls. Each has its own tanks, hoses, lines,
etc.
