Massachusetts CDL — Air Brakes Practice Test 10

1.What does the manual say about braking with the front wheels?

Front brakes should be shut off on wet roadsFront brakes should be used only above 55 mphFront-wheel braking is the leading cause of jackknifingFront-wheel braking helps in all conditions, and skids from it are unlikely even on ice

2.How do air-operated disc brakes differ from s-cam brakes?

They use a power screw rather than an s-cam to clamp the rotorThey need no slack adjusterThey apply the brakes with hydraulic fluid instead of airThey are the most common type on large trucks

3.On a tractor or straight truck, at roughly what pressure do the spring brakes come fully on by themselves?

20 to 45 psi55 to 75 psi80 to 100 psi100 to 125 psi

4.You have just pushed through deep standing water and your brakes are soaked. How does the manual say to get them working again?

Keep the vehicle in a low gear and press the pedal gently as you drive so heat dries the brakes outPull and push the parking-brake knob repeatedly until the water clearsOpen every tank drain valve and let the system blow itself dryCoast in neutral at highway speed so airflow dries the linings

5.During inspection, a brake drum or disc must not have a crack longer than what?

One quarter inchOne inchHalf the width of the friction surfaceThe full width of the friction surface

6.In an s-cam brake, what happens when the driver presses the pedal?

A wedge is forced between the ends of the brake shoesA power screw clamps a rotor between caliper padsAir fills the brake chamber and, through the slack adjuster and camshaft, turns the s-cam so the shoes press the drumThe parking spring is released so the wheel turns freely

7.As soon as the low-air warning light and buzzer come on, what is the correct action?

Keep going until the spring brakes apply themselvesPump the pedal to build pressure back upStop the vehicle somewhere safe immediately, while you still have enough air to control brakingPull the parking-brake knob out while still moving

8.An automatic front-wheel limiting valve reduces air to the front brakes except when what happens?

The brakes are applied very hard — about 55 psi or more of application pressureThe parking brake is setThe vehicle is going down a gradeThe ABS warning lamp is lit

9.Why is it dangerous to keep rolling in a heavily loaded truck until the spring brakes grab on their own?

The springs release again as soon as the vehicle slows below 20 mphThe engine will stall the moment the springs applyBecause the springs work on only some of the axles, the loaded vehicle will travel a very long way before it stopsThe trailer brakes will lock and drag the tractor sideways

10.During the service-brake test you move forward slowly and firmly press the pedal. What are you watching for?

Whether the ABS lamp switches offHow fast the tanks refillWhether the spring brakes releasePulling to one side, an unusual feel, or a delayed stop