Five ASE T4 Brakes practice test questions, answers included.

1. Recall · Air Brakes Diagnosis and Repair

   On a truck's air system, what does the governor do when reservoir pressure reaches its cut-out setting?

   1. Sends reservoir air to the unloader so the compressor stops pumping
   2. Opens the reservoir safety valve to hold pressure at the cut-out point
   3. Closes the one-way check valves to lock air in the service reservoirs
   4. Opens the supply reservoir drain valve to bleed off the extra air
   Show the answer

   A. Correct. At cut-out the governor delivers reservoir air to the compressor's unloader, and the unloader holds the compressor in its unloaded mode: it keeps turning but no longer pumps air into the system. When pressure falls to cut-in, the governor exhausts that signal and the compressor pumps again.

   Why not the others

   B. The safety valve is a separate overpressure device set well above cut-out, and the governor has no connection to it. It vents only if the governor or unloader fails to stop the compressor from pumping.

   C. One-way check valves work on their own, closing whenever the pressure behind them falls below reservoir pressure; the governor does not operate them. At cut-out the governor signals the unloader, which stops the compressor from pumping.

   D. Reservoir drain valves are opened by hand, or by their own automatic mechanism, to expel water; they are not used to control pressure. The governor controls pressure by signaling the unloader to stop the compressor pumping.

   ID T4-A-001 · Task T4-A-1.10 (ASE task list)

2. Recall · Air Brakes Diagnosis and Repair

   With the engine idling and an accurate gauge on the system, how are a truck's governor cut-out and cut-in pressures checked?

   1. Note where pressure stops rising, then stop the engine and note where it settles
   2. Note where the safety valve opens, then drain the supply tank and note where it closes
   3. Note where pressure stops rising, then fan the brakes and note where it rises again
   4. Note where the low-air warning goes out, then fan the brakes and note where it returns
   Show the answer

   C. Correct. Pressure stops rising at cut-out, when the governor unloads the compressor (often heard as the dryer purge). The brakes are then applied and released repeatedly to lower pressure, and the reading where it starts rising again is cut-in; both are compared with the manufacturer's figures.

   Why not the others

   A. Stopping the engine stops the compressor, so cut-in can never be seen, and where pressure settles reflects leakage. Fan the brakes with the engine running and note where pressure starts rising again.

   B. The safety valve is set above cut-out and should not open in normal operation, so it says nothing about the governor. Cut-out is where pressure stops rising; cut-in is where it starts rising again as the brakes are fanned.

   D. The low-air warning switches at its own low setting, well below governor cut-in, so it shows neither governor setting. Watch where pressure stops rising and where it starts rising again.

   ID T4-A-037 · Task T4-A-1.10 (ASE task list)

3. Recall · Air Brakes Diagnosis and Repair

   A service chamber with an effective diaphragm area of 24 sq in. receives 80 psi, and it drives a slack adjuster with a 6.0 in. effective arm. Ignoring return spring force and friction, about how much torque does the slack adjuster apply to the camshaft?

   1. 160 ft-lb
   2. 960 ft-lb
   3. 1,920 ft-lb
   4. 11,520 ft-lb
   Show the answer

   B. Correct. Pushrod force = 24 sq in. x 80 psi = 1,920 lb; torque = 1,920 lb x 6.0 in. = 11,520 lb-in, and 11,520 / 12 = 960 ft-lb. A larger chamber, more pressure or a longer arm raises brake torque the same way.

   Why not the others

   A. Dividing the 1,920 lb pushrod force by 12 without first multiplying by the 6.0 in. arm gives 160. Force is multiplied by the arm before converting: 1,920 x 6.0 = 11,520 lb-in, and 11,520 / 12 = 960 ft-lb.

   C. 1,920 lb is the pushrod force (24 x 80), not a torque; it still has to be multiplied by the 6.0 in. arm, giving 11,520 lb-in, or 960 ft-lb.

   D. 11,520 is the torque in lb-in (1,920 lb x 6.0 in.); calling it ft-lb skips the conversion. Divided by 12 it is 960 ft-lb.

   ID T4-A-076 · Task T4-A-2.2 (ASE task list)

4. Recall · Hydraulic Brakes Diagnosis and Repair

   A medium-duty truck has a hydraulic brake booster driven by fluid flow from the power steering pump, with an electric backup pump built into the booster. Under which condition does the electric backup pump run?

   1. Pedal applied while booster fluid flow is lost
   2. Pedal applied while booster fluid flow is normal
   3. Booster pressure above the steering relief setting
   4. Brake fluid in the master cylinder below its mark
   Show the answer

   A. Correct. A flow switch in the booster closes when fluid flow from the steering pump stops, and with the brake pedal applied that switch's signal runs the backup pump. The pump then supplies reserve assist for a controlled stop until normal flow returns.

   Why not the others

   B. With normal steering-pump flow through the booster the flow switch stays open, so the backup pump stays off however hard the pedal is pressed; the booster already has full assist. It runs when that flow is lost and the pedal is applied.

   C. High booster pressure does not switch on the backup pump. Its trigger is loss of fluid flow through the booster, sensed by the flow switch, together with a brake application; pressure relief is the steering pump's own job.

   D. The master cylinder's fluid level does not control the booster's backup pump: the booster circuit and the brake circuit are separate systems with separate fluids. The pump runs when booster flow is lost and the pedal is applied.

   ID T4-B-001 · Task T4-B-18 (ASE task list)

5. Recall · Antilock Brake System (ABS), Automatic Traction Control (ATC), Electronic Stability Control System, and Collision Warning/Avoidance System Diagnosis and Repair

   On a tractor's drive axle, which uses a relay valve and a separate air ABS modulator valve for each wheel, where is each modulator installed?

   1. Between the relay valve and that wheel's brake chamber
   2. In the control line from the treadle valve to the relay valve
   3. Between the supply reservoir and the relay valve's supply port
   4. Between the parking control valve and the spring brake chambers
   Show the answer

   A. Correct. The relay valve delivers air for the whole axle, and each modulator sits after it, at its own wheel, so the ABS module can hold or exhaust that one chamber's air without touching the other wheel. With no wheel slip the modulator simply passes the relay valve's delivery through to the chamber.

   Why not the others

   B. A valve in the relay valve's control line would act on the relay valve's signal and so on both drive wheels together. Each modulator sits downstream of the relay valve, at the chamber it controls, so one wheel can be released while the other keeps braking.

   C. A valve in the relay valve's supply would starve or feed the whole axle at once. The modulator is placed between the relay valve's delivery and one brake chamber so it can control that wheel alone.

   D. The parking control valve's line feeds the spring brake sections, which ABS does not control. ABS works on the service side, so each modulator sits between the relay valve and the service chamber of its wheel.

   ID T4-C-001 · Task T4-C-4 (ASE task list)

Want ten more with every option explained? Free T4 Brakes questions: no account, no email, printable.