Kansas CDL — Air Brakes: Safe Driving Practices Practice Test

Question 1

Before you check the slack adjusters on s-cam brakes during the walk-around, how should the truck be set up?

Accepted Answer

Parked on level ground with the wheels chocked and the parking brakes released — Stop on level ground and block the wheels with chocks so the truck can't move, then release the parking brakes. With the spring brakes off, the slack adjusters are free to move when you pull on them with gloved hands.

Answer

Parked on a slight incline with the parking brakes set so it can't roll

Answer

Engine at a fast idle with the service brake pedal held down

Answer

Parking brakes applied and the air tanks drained to zero

Question 2

Why does the manual have you test the service brakes at low speed before a trip?

Accepted Answer

It can expose a brake problem before it surprises you out in traffic — Rolling forward slowly and braking firmly lets you notice pulling to one side, an odd pedal feel, or a delayed stop. Finding those signs in the yard beats discovering them the first time you need to stop in traffic.

Answer

It builds air pressure faster

Answer

It resets the automatic slack adjusters

Answer

It warms the brakes so the parking brake holds better

Question 3

How did the s-cam brake get its name?

Accepted Answer

Its cam is shaped like the letter S — The cam that spreads the brake shoes apart is shaped like the letter S. That shape gives the most common type of air-operated foundation brake its name.

Answer

The S stands for 'spring'

Answer

The S stands for 'service'

Answer

It was named for the S-shaped air line that feeds it

Question 4

You're about to pull an old trailer built before ABS was required, and you can't tell whether it was fitted with ABS. What does the manual suggest looking for underneath it?

Accepted Answer

An electronic control unit (ECU), plus wheel speed sensor wires running out of the rear of the brakes — For towed units built before the Department of Transportation required ABS, it can be hard to tell. Look under the unit for the ECU and for wheel speed sensor wires emerging from the rear of the brakes. On other vehicles, the manufacture date on the certification label tells you whether ABS was required.

Answer

A red air line running to the front of each brake chamber

Answer

A second set of brake chambers mounted on every axle

Answer

A blue diamond-shaped decal next to the trailer's air couplers

Question 5

During a pre-trip inspection you suspect a truck's brakes have far too much slack. What is the main danger if that goes unfixed?

Accepted Answer

The vehicle can be very hard to stop — Too much brake slack can make a vehicle very hard to stop. Brakes out of adjustment are also the problem roadside inspectors find most often, so the slack adjusters deserve a careful check.

Answer

The ABS lamp will stay on

Answer

The compressor will run nonstop

Answer

The spring brakes will refuse to release

Question 6

Your air compressor is belt-driven. What should you check about the belt during the engine compartment step?

Accepted Answer

Its condition and how tight it is — For a belt-driven compressor, the manual's Step 2 check is the belt's condition and its tightness. The belt should be in good shape.

Answer

Only that a belt is present

Answer

That it slips slightly at idle to protect the compressor

Answer

The part number printed on it

Question 7

Which of these is NOT one of the foundation brake types described in the manual's Air Brakes section?

Accepted Answer

Band brakes — The manual describes three foundation brakes used at the wheels: s-cam drum brakes (the most common), wedge brakes, and air-operated disc brakes. Band brakes are not among them.

Answer

S-cam drum brakes

Answer

Wedge brakes

Answer

Disc brakes

Question 8

On an older air-braked truck, the yellow ABS malfunction lamp is still on as you creep out of the yard. Up to what point can the lamp on older systems normally stay lit?

Accepted Answer

Until you are moving faster than about 5 mph — Newer systems light the lamp briefly at start-up as a bulb check. Older systems may keep it on until the vehicle is going faster than about 5 mph. A lamp that stays lit beyond that point deserves attention.

Answer

Until air pressure reaches the governor's cut-out level

Answer

Until the engine has run for about five minutes

Answer

Until a mechanic resets it at the shop

Question 9

Air-operated disc brakes begin applying force the same way s-cam brakes do. Which two parts do they share for that job?

Accepted Answer

A brake chamber and a slack adjuster — In an air disc brake, air pushes on a brake chamber, which works a slack adjuster, exactly as in an s-cam brake. The difference is what comes next: the slack adjuster turns a power screw that clamps the rotor between the caliper's lining pads instead of turning an s-cam.

Answer

Brake shoes and a brake drum

Answer

An s-cam and a return spring

Answer

A wedge and a front brake limiting valve

Question 10

In an emergency, you hand-adjust an automatic slack adjuster so you can get the truck to a repair shop. What should you expect afterward?

Accepted Answer

The brake will probably slip out of adjustment again soon, because the cause hasn't been fixed — Hand-adjusting an automatic adjuster is only a stopgap for an emergency. It usually leaves the underlying fault in place, so the brake is likely to drift out of adjustment again before long. Have a shop correct the problem promptly.

Answer

The adjuster is now repaired for good

Answer

The adjuster will stay in manual mode from now on

Answer

That brake will now apply harder than the others

Question 11

On an older single air brake system (pre-1975), the typical buildup check is 50 to 90 psi within 3 minutes. At what engine speed is that measured?

Accepted Answer

An idle of about 600 to 900 rpm — For pre-1975 single air systems, the manual's typical requirement is a climb from 50 psi to 90 psi in no more than 3 minutes while the engine idles at 600-900 rpm. Dual air systems are checked differently: at operating rpm, from 85 to 100 psi.

Answer

Full governed engine speed

Answer

Operating rpm with the vehicle under load

Answer

Any speed, as long as the parking brake is released

Question 12

You're driving a truck built before 1975 that has a front brake limiting valve control in the cab. The roads are icy this morning. Where should you set the control?

Accepted Answer

'Normal,' so you keep the vehicle's full stopping power — The 'slippery' setting halves the air sent to the front brakes, which cuts the vehicle's stopping power. Testing has found that front-wheel skids from braking are unlikely even on ice, so the manual says to keep the control at 'normal.'

Answer

'Slippery,' so the front wheels can't skid

Answer

'Slippery' until the brakes warm up, then 'normal'

Answer

Halfway between the two positions

Kansas CDL — Air Brakes: Safe Driving Practices practice test

Study questions with answers

1. Before you check the slack adjusters on s-cam brakes during the walk-around, how should the truck be set up?

2. Why does the manual have you test the service brakes at low speed before a trip?

3. How did the s-cam brake get its name?

4. You're about to pull an old trailer built before ABS was required, and you can't tell whether it was fitted with ABS. What does the manual suggest looking for underneath it?

5. During a pre-trip inspection you suspect a truck's brakes have far too much slack. What is the main danger if that goes unfixed?

6. Your air compressor is belt-driven. What should you check about the belt during the engine compartment step?

7. Which of these is NOT one of the foundation brake types described in the manual's Air Brakes section?

8. On an older air-braked truck, the yellow ABS malfunction lamp is still on as you creep out of the yard. Up to what point can the lamp on older systems normally stay lit?

9. Air-operated disc brakes begin applying force the same way s-cam brakes do. Which two parts do they share for that job?

10. In an emergency, you hand-adjust an automatic slack adjuster so you can get the truck to a repair shop. What should you expect afterward?

11. On an older single air brake system (pre-1975), the typical buildup check is 50 to 90 psi within 3 minutes. At what engine speed is that measured?

12. You're driving a truck built before 1975 that has a front brake limiting valve control in the cab. The roads are icy this morning. Where should you set the control?

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