What is the air compressor’s job in an air brake system?
Correct answer: Pump air into the storage tanks
The compressor supplies compressed air to the reservoirs used by the brake system.
Source: Texas DL-7C, March 2026, section 5, PDF page 81: Air compressor ↗
At approximately what tank pressure does the governor normally cut out the air compressor?
Correct answer: 125 psi
The governor normally stops compressor loading near 125 psi, although manufacturer specifications may vary.
Source: Texas DL-7C, March 2026, section 5, PDF page 81: Governor ↗
At approximately what pressure does the governor normally allow the compressor to cut in again?
Correct answer: 100 psi
As reservoir pressure falls to roughly 100 psi, the governor normally restarts compressor loading.
Source: Texas DL-7C, March 2026, section 5, PDF page 81: Governor ↗
Why must moisture and oil be removed from air storage tanks?
Correct answer: Water can freeze and interfere with braking
Water and oil collect in the tanks; frozen water can obstruct the system and cause brake failure.
Source: Texas DL-7C, March 2026, section 5, PDF page 81: Air tanks ↗
When should manually drained air tanks normally be emptied?
Correct answer: At the end of each driving day
Manual tank drains should be opened completely at the end of each day of driving.
Source: Texas DL-7C, March 2026, section 5, PDF page 81: Air tanks ↗
What does the air-system safety valve protect against?
Correct answer: Excessive pressure
The valve protects the first tank and the rest of the system from overpressure and usually opens near 150 psi.
Source: Texas DL-7C, March 2026, section 5, PDF page 82: Safety valve ↗
Why should a driver avoid unnecessary repeated brake-pedal applications?
Correct answer: They can use air faster than the compressor replaces it
Each release exhausts compressed air, so repeated applications may lower pressure to an unsafe level.
Source: Texas DL-7C, March 2026, section 5, PDF page 82: Brake pedal ↗
What can increasing application pressure needed to hold the same speed indicate?
Correct answer: The brakes may be fading
A rising application-pressure requirement can signal brake fade, poor adjustment, leaks, or mechanical trouble.
Source: Texas DL-7C, March 2026, section 5, PDF page 83: Application gauge ↗
In the Texas handbook section 5.3.3 low-pressure warning check, the warning must activate before pressure falls below what threshold?
Correct answer: 55 psi
Section 5.3.3 gives 55 psi as the threshold. A vehicle can warn earlier; follow its specifications and stop safely when the warning activates.
Source: Texas DL-7C, March 2026, section 5, PDF page 87: Low-air warning ↗
What holds spring brakes off while a vehicle is being driven normally?
Correct answer: Air pressure
Air pressure compresses the powerful springs; loss of pressure lets the springs apply the brakes.
Source: Texas DL-7C, March 2026, section 5, PDF page 83: Spring brakes ↗
At what approximate pressure range do tractor and straight-truck spring brakes come fully on?
Correct answer: 20 to 45 psi
Spring brakes normally apply automatically as pressure falls into the 20-45 psi range.
Source: Texas DL-7C, March 2026, section 5, PDF page 83: Spring brakes ↗
On a newer air-brake vehicle, how is the parking brake normally applied?
Correct answer: Pull out the yellow diamond-shaped control
Pulling out the yellow push-pull knob releases air from the spring brakes so they apply.
Source: Texas DL-7C, March 2026, section 5, PDF page 83: Parking brakes ↗
Why should the foot brake not be pressed while spring brakes are already applied?
Correct answer: Combined spring and air forces may damage the brakes
Some systems can be damaged when air pressure adds to the force of applied spring brakes.
Source: Texas DL-7C, March 2026, section 5, PDF page 83: Parking brakes ↗
If the ABS malfunction lamp stays on, what braking capability remains?
Correct answer: Normal braking remains, but ABS needs service
An ABS fault does not remove normal brakes; drive normally and arrange service promptly.
Source: Texas DL-7C, March 2026, section 5, PDF page 88: ABS ↗
On an S-cam brake, what movement suggests a reachable slack adjuster may need adjustment?
Correct answer: More than about one inch at the push-rod connection
With wheels chocked and parking brakes released, manually pulling a reachable S-cam slack adjuster more than about one inch at the push-rod connection signals trouble. This is not a universal applied push-rod stroke limit. Have faults repaired; routinely adjusting automatic adjusters is not a substitute for repair.
Source: Texas DL-7C, March 2026, section 5, PDF page 86: Slack adjusters ↗
During a one-minute applied leakage test, what is the maximum pressure drop for a single vehicle?
Correct answer: 3 psi
Secure the vehicle, charge the system, shut off the engine, and release the parking brakes. Fully apply the foot brake and let the initial pressure drop stabilize before timing one minute. A single vehicle must not then lose more than 3 psi.
Source: Texas DL-7C, March 2026, section 5, PDF page 87: Applied leakage ↗
During a one-minute applied leakage test, what is the maximum drop for a two-vehicle air-brake combination?
Correct answer: 4 psi
With both vehicles air-braked, secure the combination, charge the system, shut off the engine, and release parking brakes. Fully apply the foot brake. After the initial drop stabilizes, loss must not exceed 4 psi in one minute.
Source: Texas DL-7C, March 2026, section 5, PDF page 87: Applied leakage ↗
In the Texas section 5.3.3 static leakage check, what loss rate should a single vehicle stay below?
Correct answer: 2 psi in one minute
Secure the vehicle against rolling, fully charge the system, stop the engine and release the brakes. The chapter specifies a loss rate of less than 2 psi per minute for a single vehicle.
Source: Texas DL-7C, March 2026, section 5, PDF page 86: Static leakage ↗
At operating engine rpm, what buildup does Texas section 5.3.3 specify for a typical dual air system?
Correct answer: 85 to 100 psi within 45 seconds
Check at operating rpm, not simply normal idle. The handbook allows that larger-than-minimum air tanks may take longer; consult manufacturer specifications.
Source: Texas DL-7C, March 2026, section 5, PDF page 87: Pressure buildup ↗
How should service brakes be checked after normal air pressure is restored?
Correct answer: Move forward slowly at about 5 mph and apply them firmly
A low-speed firm application can reveal pulling, unusual feel, or delayed stopping.
Source: Texas DL-7C, March 2026, section 5, PDF page 87: Service brake test ↗
