CDL air brakes practice test 3

A: The shoes and linings must move farther to reach the drums, and the force of contact is reduced. As overheated drums expand, the shoes and linings have to move farther to contact them, and the force of that contact is reduced. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.5 Brake Fading or Failure, page 5-9.

B: Something is wrong, and a mechanic should fix it. If the safety valve releases air, something is wrong with the system, and you should have a mechanic fix the fault. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.6 Safety Valve, page 5-2.

B: Don't drive until the problem is fixed. If air pressure doesn't build fast enough, it may drop too low while you drive and force an emergency stop. Don't drive until it's fixed. Commercial Driver's License Manual (CDL Driver's Manual): 5.3.3 Step 7 Final Air Brake Check, page 5-7.

D: They stop doing their share early, so the other brakes overheat and fade. Brakes out of adjustment stop doing their share before those that are adjusted. The other brakes can then overheat and fade, leaving too little braking to control the vehicle. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.5 Brake Fading or Failure, page 5-9.

C: The foot valve or treadle valve. The manual says the brake pedal is also called the foot valve or treadle valve. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.7 The Brake Pedal, page 5-2.

A: You lose steering control. When your steering wheels lock up, you lose steering control. When other wheels lock, you may skid, jackknife, or spin. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.2 Braking with Antilock Brakes, page 5-8.

B: When they are hot. Hot brakes can drift out of adjustment fast, so check adjustment frequently. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.5 Brake Fading or Failure, page 5-9.

C: More air pressure is applied to the brakes. Pushing the pedal down harder applies more air pressure to the brakes. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.7 The Brake Pedal, page 5-2.

D: It reduces braking pressure to a safe level so you keep control. The ABS computer senses impending lockup and reduces braking pressure to a safe level, so you keep control. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.2 Braking with Antilock Brakes, page 5-8.

A: They are only a supplement to the braking effect of the engine. On long or steep downgrades the engine does the main braking work and the service brakes only add to it. Get into the proper low gear before starting down. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.6 Proper Braking Technique, page 5-9.

D: It can let air out faster than the compressor can replace it. Each release lets some air out of the system. Fanning the pedal can let air out faster than the compressor replaces it, and if pressure gets too low the brakes won't work. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.7 The Brake Pedal, page 5-2.

D: Let up on the brakes, if you can safely do so. With ABS only on the tractor you should keep steering control, but the trailer can still swing. If it starts to, ease off the brakes when it is safe to do so. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.2 Braking with Antilock Brakes, page 5-8.

D: Brake hard enough to feel a definite slowdown, release at about 5 mph below your safe speed, and repeat when you reach the safe speed again. Apply the brakes just hard enough to feel a definite slowdown, release them when you are about 5 mph below your safe speed, and repeat when your speed climbs back to the safe speed. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.6 Proper Braking Technique, page 5-9.

C: S-cam drum brake. Foundation brakes are used at each wheel, and the most common type is the S-cam drum brake. Wedge and disc brakes are less common. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.8 Foundation Brakes, page 5-2.

C: Let up on the brakes, if you can safely do so, until you regain control. ABS on only the trailer makes trailer swing less likely, but the tractor can still lose steering or jackknife. If that starts, ease off the brakes when it is safe until control returns. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.2 Braking with Antilock Brakes, page 5-8.

B: About 3 seconds. The manual says each brake application should last about three seconds. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.6 Proper Braking Technique, page 5-9.

D: Brake shoes and linings pushed against the inside of the drum, causing friction. The shoes and linings are pressed against the inside of the brake drum; the friction slows the vehicle and creates heat. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.8 Foundation Brakes, page 5-2.

C: If you always drive a straight truck or combination with working ABS on all axles. Normally you brake as usual even with ABS. The one exception: a driver who always drives a straight truck or combination with working ABS on every axle may brake fully in an emergency stop. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.2 Braking with Antilock Brakes, page 5-8.

A: When your speed is down to about 35 mph. Using the manual's example: with a safe speed of 40 mph, don't brake until you reach 40, then brake hard enough to slow to 35 mph and release. Repeat as needed. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.6 Proper Braking Technique, page 5-9.

A: Air is let into each brake chamber. Pushing the pedal lets air into each brake chamber. Air pressure then pushes the rod out, moving the slack adjuster and twisting the brake camshaft. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.8 Foundation Brakes, page 5-2.

A: In a way that keeps the vehicle in a straight line and lets you turn if needed. Brake in a way that keeps the vehicle in a straight line and allows you to turn if it becomes necessary, using controlled braking or stab braking. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.3 Emergency Stops, page 5-8.

C: Use the brakes lightly while driving in a low gear to heat and dry them. Dry wet brakes by applying them lightly as you drive in a low gear, so the heat dries them out. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.8 Parking Brakes, page 5-9.

C: It twists the brake camshaft, which turns the S-cam. The push rod moves the slack adjuster, which twists the brake camshaft and turns the S-cam that spreads the shoes against the drum. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.8 Foundation Brakes, page 5-2.

B: Applying the brakes as hard as you can without locking the wheels, with very small steering movements. With controlled braking you brake as hard as you can without locking the wheels and keep steering movements very small. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.3 Emergency Stops, page 5-8.

B: It is shaped like the letter S. The manual says the S-cam gets its name because it is shaped like the letter S. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.8 Foundation Brakes, page 5-2.