Michigan CDL Air Brakes Test
Questions & Verified Answers
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.
3 different braking systems that make up Air Brakes - correct answer ✔✔Service Brake, Parking
Brake, Emergency Brake
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).
Questions & Verified Answers
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.
3 different braking systems that make up Air Brakes - correct answer ✔✔Service Brake, Parking
Brake, Emergency Brake
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).
