Ten ASE T4 Brakes questions in the ASE format: four options, one best answer. They are free to use, print and share, and there is nothing to sign up for on this page.
01How to use these
The questions come from the ToolboxPrep T4 bank and are spread across the test's content areas in the proportion the ASE test specification gives them: A (Air Brakes Diagnosis and Repair), B (Hydraulic Brakes Diagnosis and Repair), C (Antilock Brake System (ABS), Automatic Traction Control (ATC), Electronic Stability Control System, and Collision Warning/Avoidance System Diagnosis and Repair). Answer each one before opening the explanation. Every explanation covers all four options, because knowing why the wrong answers are wrong is most of the skill.
- Pace. The T4 test gives you 75 minutes for 60 questions (50 scored, 10 unscored), about 1 min 15 s a question. Try these at that pace.
- Print. The printed version shows the questions and the answer key without the explanations, so it works as a handout.
02The questions
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A tractor's low-air warning stays on after the system has built to 120 psi, confirmed by a test gauge at the primary reservoir. The warning lights when a normally closed pressure switch grounds the warning circuit. Unplugging the wire at the switch turns the warning off. This could be caused by:
- a warning wire chafed through to ground.
- a pressure switch whose contacts stay closed.
- reservoir pressure lower than the dash gauge shows.
- an open in the wire between the cluster and the switch.
Show the answer
B. Correct. With 120 psi on it the switch's contacts should be open; unplugging its wire removed the ground and the warning went out, so the wiring and the cluster are working and the switch is holding the circuit closed. Replace the switch, then confirm the warning goes out above its setting and comes on when pressure is lowered below it.
Why not the others
A. A warning wire grounded between the cluster and the switch would keep the warning on even with the switch unplugged, because that ground would remain. The warning went out when the switch was disconnected, so the ground is through the switch itself.
C. The test gauge at the reservoir confirms 120 psi, so the system really is above the warning point. The fault is in the warning circuit: the switch is grounding it when it should be open.
D. An open in the switch wire would keep the warning from lighting at all, even at low pressure. Here the warning stays on until the switch is unplugged, which points to a switch stuck closed.
ID T4-A-002 · Task T4-A-1.5 (ASE task list)
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What do the two needles of a tractor's dual air pressure gauge show?
- Primary and secondary service reservoir pressures
- Supply reservoir pressure and brake application pressure
- Service reservoir pressure and trailer supply pressure
- Compressor discharge pressure and supply reservoir pressure
Show the answer
A. Correct. Each needle reads one service reservoir, so the driver can see the pressure in each of the two brake circuits and spot a loss in either. Where brake application pressure is displayed, it has a separate gauge.
Why not the others
B. Application pressure, where it is shown, has its own gauge, and the supply reservoir is not what the dual gauge reads. Its needles show the primary and secondary service reservoir pressures.
C. Trailer supply pressure is not what the second needle shows. The two needles read the primary and secondary service reservoirs, one for each brake circuit.
D. Compressor discharge pressure is not displayed in the cab. The dual gauge reads the primary and secondary service reservoirs so the driver can watch both brake circuits.
ID T4-A-019 · Task T4-A-1.4 (ASE task list)
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A nylon air line is being fitted into a push-to-connect fitting. How should the tubing be prepared and installed?
- Cut it with side cutters and push it in until it first catches hold
- Cut it at an angle so it slides past the seal and push it in
- Cut it square with a tubing cutter and push it in to full depth
- Cut it square and coat the end with thread sealant first
Show the answer
C. Correct. A square, clean cut lets the tube seat against the fitting's O-ring and gripping collet, and pushing it to full depth (often to a marked insertion line) seats it past both. Tug on it afterward to confirm it is locked.
Why not the others
A. Side cutters pinch the tube out of round, and stopping at the first catch leaves the end short of the O-ring, so it leaks or pulls out under pressure. Cut it square with a tubing cutter and push it to full depth.
B. An angled end can cut or roll the O-ring and leaves part of the tube short of full depth, so the joint leaks or pulls out. The tube is cut square and pushed in to full depth.
D. Thread sealant on the tube can foul the O-ring and the collet and adds nothing to the seal, which the O-ring makes on the clean outside of the tube. Cut it square and push it in to full depth.
ID T4-A-031 · Task T4-A-1.11 (ASE task list)
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Under 49 CFR 393.47(e), what is the brake readjustment limit for a type 24 clamp-type brake chamber with a 3-in. rated stroke?
- 1 3/4 in.
- 2 in.
- 2 1/4 in.
- 2 1/2 in.
Show the answer
D. Correct. The 393.47(e) clamp-type table lists a type 24 chamber at 1 3/4 in. for standard stroke and 2 in. for long stroke, with a footnoted 2 1/2 in. for type 24 chambers that have a 3-in. rated stroke. Read the chamber's tag for its type and rated stroke before comparing a measured stroke with any limit.
Why not the others
A. 1 3/4 in. is the rule's limit for a type 24 standard-stroke chamber. A type 24 chamber with a 3-in. rated stroke is allowed 2 1/2 in.
B. 2 in. is the limit the rule lists for a type 24 long-stroke chamber without the 3-in. rated stroke. With a 3-in. rated stroke, the limit is 2 1/2 in.
C. 2 1/4 in. is not listed for any clamp-type chamber; the rule gives it for other actuator designs, such as the type 30 rotochamber. A type 24 clamp chamber with a 3-in. rated stroke has a 2 1/2 in. limit.
ID T4-A-046 · Task T4-A-2.3 (ASE task list) · 49 CFR 393.47
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Under the federal motor carrier safety rules, within what range of the towing vehicle's air pressure must its tractor protection valve or similar device operate automatically?
- 5 to 15 psi
- 20 to 45 psi
- 60 to 75 psi
- 85 to 100 psi
Show the answer
B. Correct. 49 CFR 393.43(a) requires the tractor protection valve or similar device on an air-braked towing vehicle to operate automatically when its air pressure is between 20 and 45 psi. Closing in that range saves the tractor's remaining air for its own service brakes after a breakaway or a major trailer leak.
Why not the others
A. Waiting until the tractor fell to 5 to 15 psi would leave too little air for its own service brakes after a breakaway. The rule sets automatic operation between 20 and 45 psi.
C. That range is above the 20 to 45 psi the rule sets for automatic operation of the tractor protection valve or similar device.
D. That is up near normal working pressure; the rule sets automatic operation of the tractor protection valve or similar device at 20 to 45 psi.
ID T4-A-061 · Task T4-A-1.18 (ASE task list) · 49 CFR 393.43
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On a truck's S-cam brake, what is the job of the spacer washers fitted on the camshaft between the slack adjuster and its retaining snap ring?
- Sealing grease into the bracket bushing
- Setting the slack adjuster's effective arm length
- Limiting how far the camshaft moves endwise
- Setting the shoe-to-drum running clearance
Show the answer
C. Correct. The spacer washers take up the camshaft's axial free movement so that end play stays within the manufacturer's limit and the slack adjuster cannot shift along the camshaft spline. Too much end play lets the cam and slack adjuster wander as the brake applies.
Why not the others
A. The bushing's grease seals do that job. The washers are spacers that take up camshaft end play.
B. Effective arm length is the distance from the camshaft center to the clevis pin hole, fixed by the slack adjuster and the hole used; washers on the camshaft do not change it. They limit camshaft end play.
D. Running clearance is set by the slack adjuster's adjusting mechanism, not by washers on the camshaft. The washers limit camshaft end play.
ID T4-A-084 · Task T4-A-2.4 (ASE task list)
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A tractor's rear drive axle is being relined. Technician A says the drums need not be measured, because they were within limits at the last inspection. Technician B says linings with a higher friction rating than the other axles' should be fitted so that this axle stops harder. Who is right?
- A only
- B only
- Both A and B
- Neither A nor B
Show the answer
D. Correct. Technician A is wrong: drums keep wearing after an inspection, so they are measured at the reline against the manufacturer's limits before new linings go in. Technician B is wrong: linings are chosen to the friction rating the vehicle or axle manufacturer specifies, because a higher-friction axle takes more than its share of the braking, wears faster and upsets the balance between axles.
Why not the others
A. Technician A is wrong: drums wear with every stop and are measured at each reline, since a new lining needs a drum within its limits. Technician B is wrong too: fitting a higher friction rating than specified upsets the brake balance between axles.
B. Technician B is wrong: a friction rating higher than the manufacturer specifies makes that axle take more than its share of braking, overheat and wear fast. Technician A is wrong too: the drums are measured at every reline.
C. Neither technician is right. Technician A would skip the drum measurement that every reline needs, and Technician B would upset the balance between axles by fitting a friction rating other than the one specified.
ID T4-A-097 · Task T4-A-2.7 (ASE task list)
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A medium-duty truck's transmission-mounted drum parking brake will not hold the truck on a grade. With the drum removed, the shoes are soaked with oil, and the transmission's output shaft area behind the drum is wet with the same oil. Which repair is needed?
- Clean the shoes with brake cleaner and readjust them
- Replace the output seal and shoes and clean the drum
- Replace the shoes and readjust the parking brake cable
- Replace the output seal and clean the shoes and drum
Show the answer
B. Correct. Oil-soaked linings cannot be cleaned back to a safe friction surface, so the shoes are replaced, and the leaking output seal is replaced too or the new shoes will soon be soaked again. The drum is cleaned of oil before reassembly and the brake adjusted by the manufacturer's procedure.
Why not the others
A. Brake cleaner removes surface oil but cannot draw it out of the lining material, so the shoes would keep slipping, and the seal would keep leaking. The seal and the shoes are replaced and the drum is cleaned.
C. New shoes would soon be soaked again because the output seal is still leaking, and a cable adjustment does not restore lost lining friction. The seal is replaced along with the shoes, and the drum is cleaned.
D. Fixing the seal stops the leak, but brake cleaner removes only surface oil and cannot draw it out of soaked lining material, so the cleaned shoes would still slip. The shoes are replaced along with the seal, and the drum is cleaned.
ID T4-B-002 · Task T4-B-15 (ASE task list)
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A truck's floating front calipers are wearing out the right front pads far sooner than the left. Each of these can cause that EXCEPT:
- a right front piston that does not retract.
- seized slide pins on the right front caliper.
- a rear proportioning valve that is stuck open.
- a right front hose that traps pressure on release.
Show the answer
C. Correct. A proportioning valve controls rear brake pressure, so even a stuck-open valve affects the rear brakes and not one front wheel. Faster wear at one front wheel points at something keeping that caliper applied, which is found by checking for drag with the wheel raised and the pedal released.
Why not the others
A. This could cause it: a piston corroded in its bore holds its pad against the rotor after release, wearing that wheel's pads quickly.
B. This could cause it: seized slides keep the caliper from floating back, so the pads stay against the rotor and wear faster on that wheel.
D. This could cause it: a hose whose inner lining has collapsed can act as a check valve, holding pressure in the caliper after release so the pads drag and wear.
ID T4-B-023 · Task T4-B-9 (ASE task list)
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During a hard stop on wet pavement with an empty trailer, the trailer's tandem wheels lock and skid while the tractor stops straight with its own ABS working. The tractor's ABS lamp is off, but its dash-mounted trailer ABS lamp has been on since the trailer was coupled. Which of these is the most likely cause?
- A fault in the tractor's ABS module that also runs the trailer
- A trailer ABS fault that has shut off its antilock control
- A tractor protection valve passing low trailer service pressure
- Mismatched tire sizes on the tractor's steer and drive axles
Show the answer
B. Correct. The trailer's ABS has its own module, and the dash-mounted trailer ABS lamp reports that module's status. When it detects a fault it turns off antilock control where the fault affects it, so a lightly loaded trailer's brakes work conventionally and can lock on wet pavement; read the trailer module's DTCs next.
Why not the others
A. The tractor's ABS lamp is off and the tractor stopped straight under ABS control, so its module is working. A trailer's antilock is run by the trailer's own ABS module, whose faults light the trailer ABS lamp.
C. Low trailer service pressure would weaken the trailer brakes, making lock-up less likely, and it would not light the trailer ABS lamp. The lamp points to a fault the trailer's ABS module has found.
D. Tractor tire sizes matter only to the tractor module's wheel speed comparison, and the tractor stopped straight under ABS with its lamp off. They have no effect on the trailer's antilock, which its own module controls.
ID T4-C-002 · Task T4-C-1 (ASE task list)
03Answer key
| Question | Answer | Content area |
|---|---|---|
| Q1 | B | Air Brakes Diagnosis and Repair |
| Q2 | A | Air Brakes Diagnosis and Repair |
| Q3 | C | Air Brakes Diagnosis and Repair |
| Q4 | D | Air Brakes Diagnosis and Repair |
| Q5 | B | Air Brakes Diagnosis and Repair |
| Q6 | C | Air Brakes Diagnosis and Repair |
| Q7 | D | Air Brakes Diagnosis and Repair |
| Q8 | B | Hydraulic Brakes Diagnosis and Repair |
| Q9 | C | Hydraulic Brakes Diagnosis and Repair |
| Q10 | B | Antilock Brake System (ABS), Automatic Traction Control (ATC), Electronic Stability Control System, and Collision Warning/Avoidance System Diagnosis and Repair |
04Questions by content area
Working on one part of the T4 test? Each content area has its own page with five more free questions.
05More free questions
The T4 study guide covers each content area and how to study for it, and the ASE T4 Brakes practice test page describes the full T4 question bank. The same free format is available for the other 15 tests.
How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.
ToolboxPrep is an independent study site, not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original, written from ASE’s published test specifications and task lists and other public sources. They are not actual ASE test questions and not recalled or “brain dump” questions. ASE is a trademark of its owner, and we never use the ASE logo. Standards and service information are cited, not reproduced.