A reservoir is fitted with an automatic drain (spitter) valve. What does 49 CFR 393.50 require of it?49 CFR 393.50, paragraph (d). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
A tractor has a foot valve and a separate hand valve for the trailer brakes. What does 49 CFR 393.49 require of the braking system?49 CFR 393.49, paragraph (a). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
A tractor has two means of activating the emergency features of the trailer brakes. One is automatic. What must the other be, under 49 CFR 393.43?49 CFR 393.43, paragraph (b). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
A trailer breaks away from its tractor. For how long must its brakes stay applied, under 49 CFR 393.43?49 CFR 393.43, paragraph (d). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
Show all 50 questions (46 more)
Air supply and service systems, continued
A truck has no air dryer. What can the supply system be equipped with as an alternative?Wikipedia, Air brake (road vehicle), Supply system. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
An air brake complaint is to be diagnosed. What does the Navy manual say to do first, before the air buildup and leakage tests?US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 6, Inspecting and Troubleshooting Brake Systems, Troubleshooting Air Brake Systems. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
Check valves protect each service reservoir against a loss of air from a failure on the supply side. How must their proper functioning be checkable, under 49 CFR 393.50?49 CFR 393.50, paragraph (c). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
The dash gauge shows air pressure above normal. What does the Navy air brake chart say to check first?US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 6, Inspecting and Troubleshooting Brake Systems, Troubleshooting Air Brake Systems, Table 6-3. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
How does the Navy manual test that trailer brakes hold as if the trailer had suddenly come loose from the tractor?US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 6, Inspecting and Troubleshooting Brake Systems, Troubleshooting Air Brake Systems. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
On a tractor with relay valves, where does the air that fills the rear service brake chambers come from?Wikipedia, Air brake (road vehicle), Control system. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
Reservoir pressure reaches the governor cut-out setting. What happens in the compressor once the unloading valves are forced off their seats, by TM 9-8000?US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
What is a quick release valve provided for, by TM 9-8000?US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
Which two air lines make up the trailer brake system of a tractor and semitrailer?Wikipedia, Air brake (road vehicle), Control system. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
Why can an air brake system not run out of its operating fluid in the way a hydraulic system can?Wikipedia, Air brake (road vehicle), Advantages. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
Why do towed vehicles use no-bleed-back relay emergency valves, under 49 CFR 393.43?49 CFR 393.43, paragraph (e). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A1. Air Brakes: Air Supply and Service Systems (15 of 50)
Foundation brakes and wheel hubs 13
A brake actuator is of a type not listed in the stroke tables. What pushrod stroke fails the periodic inspection, by Appendix A to 49 CFR Part 396?49 CFR Part 396, Appendix A (Minimum Periodic Inspection Standards), section 1, Brake System, a(5)(b). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
A brake drum shows short hairline heat check cracks and no other damage. How does Appendix A to 49 CFR Part 396 treat them?49 CFR Part 396, Appendix A (Minimum Periodic Inspection Standards), section 1, Brake System, c. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
A camshaft support bracket is found loose in the periodic inspection. How does Appendix A to 49 CFR Part 396 treat it?49 CFR Part 396, Appendix A (Minimum Periodic Inspection Standards), section 1, Brake System, a(3). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
A truck has air disc brakes on its drive axles. Below what pad thickness may it not be operated, under 49 CFR 393.47?49 CFR 393.47, paragraph (d)(2). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
A truck has wedge brakes. How far may the scribe mark on the lining move before the brake fails the periodic inspection, by Appendix A to 49 CFR Part 396?49 CFR Part 396, Appendix A (Minimum Periodic Inspection Standards), section 1, Brake System, a, Wedge Brake Data. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
A wheel bearing race has small dents that match the roller spacing. The hub took a heavy blow while standing still. What is this permanent deformation called?Wikipedia, Brinelling, lead section. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
Brake linings on one wheel end are found soaked. Which contamination fails the lining in Appendix A to 49 CFR Part 396?49 CFR Part 396, Appendix A (Minimum Periodic Inspection Standards), section 1, Brake System, a(6). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
Flakes of metal have broken away from the roller path of a wheel bearing race. Where does mechanical spalling occur?Wikipedia, Spall, Mechanical spalling. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
Replacement linings are chosen for a truck. What kind of material are brake linings made of?Wikipedia, Brake lining, Structure and function. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
What does TM 9-8000 say a brake chamber does?US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
What does turning the shaft of an S-cam brake do?Wikipedia, S-cam, lead section. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
What two things does TM 9-8000 say a slack adjuster does?US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
Why are disc brakes much more resistant to brake fade than drum brakes?Wikipedia, Brake fade, lead section. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A2. Air Brakes: Mechanical/Foundation and Wheel Hub (13 of 50)
Parking brakes 4
A tractor with a failed air system must be towed. Why must its spring brakes be wound off (caged) by hand first?Wikipedia, Air brake (road vehicle), Disadvantages. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A3. Air Brakes: Parking Brakes (4 of 50)
In the periodic inspection, which parking brake finding fails a vehicle, by Appendix A to 49 CFR Part 396?49 CFR Part 396, Appendix A (Minimum Periodic Inspection Standards), section 1, Brake System, b. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A3. Air Brakes: Parking Brakes (4 of 50)
Two technicians discuss the spring brakes of an air-braked truck. Technician A says air pressure is used to hold the parking brakes off. Technician B says powerful springs hold the parking brakes on. Who is right?Wikipedia, Parking brake, Large vehicles. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A3. Air Brakes: Parking Brakes (4 of 50)
Under which loading must the parking brake of an air-braked truck hold the vehicle or combination stationary, by 49 CFR 393.41?49 CFR 393.41, paragraph (b). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), A3. Air Brakes: Parking Brakes (4 of 50)
Hydraulic brakes 11
A hydraulic-braked truck has a GVWR over 10,000 pounds. Which fault must have an indicator lamp of its own, under FMVSS No. 105?49 CFR 571.105 (FMVSS No. 105, Hydraulic and electric brake systems), S5.3. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
A medium truck has a driveline (transmission) parking brake. Why may the vehicle still move with that brake applied, by TM 9-8000?US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-20, Advantages and Disadvantages of Transmission Brakes. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
A truck with air-over-hydraulic brakes has a faulty power cylinder. Technician A says a hard pedal can result. Technician B says dragging brakes can result, when the cylinder fails to return to the released position. Who is right?US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 6, Inspecting and Troubleshooting Brake Systems, Air-Over-Hydraulic. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
A truck with hydraulic drum brakes is inspected. Below what lining thickness at the shoe center may its rear axle brakes not be operated, under 49 CFR 393.47?49 CFR 393.47, paragraph (d)(2). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
The belt that drives the power steering pump breaks on a truck with a hydraulic-power booster. About how many assisted brake applications does the accumulator still give, by TM 9-8000?US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-37, Hydraulic-Power Booster. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
From which date of manufacture must a commercial motor vehicle with a hydraulic brake system have automatic brake adjusters, under 49 CFR 393.53?49 CFR 393.53, paragraph (a). Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
In the air-hydraulic cylinder of an air-over-hydraulic brake system, why is the hydraulic pressure much greater than the air pressure admitted?US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-40, Air-Over-Hydraulic Brake System. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
In the pressure method of bleeding hydraulic brakes, where is the pressure pump attached?Wikipedia, Brake bleeding, Methods. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
The parking brake of a hydraulic-braked truck over 10,000 pounds GVWR is tested to FMVSS No. 105. What must it do?49 CFR 571.105 (FMVSS No. 105, Hydraulic and electric brake systems), S5.2. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
What does the limiting valve of a hydraulic brake system do, by TM 9-8000?US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-31, Limiting Valve. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
What warning must be at the brake fluid reservoir of a truck with hydraulic brakes, under FMVSS No. 105?49 CFR 571.105 (FMVSS No. 105, Hydraulic and electric brake systems), S5.4.3. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), B. Hydraulic Brakes Diagnosis and Repair (11 of 50)
ABS, traction and stability control 7
A collision warning system is diagnosed after a bumper repair. Which sensors do such systems use to detect an imminent crash?Wikipedia, Collision avoidance system, lead section. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), C. Antilock Brake System, Automatic Traction Control, Electronic Stability Control and Collision Warning/Avoidance (7 of 50)
A stability control fault is diagnosed after a yaw-rate sensor was replaced. What does a yaw-rate sensor measure?Wikipedia, Yaw-rate sensor, lead section. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), C. Antilock Brake System, Automatic Traction Control, Electronic Stability Control and Collision Warning/Avoidance (7 of 50)
An ESC fault is present on a truck tractor. How must the ESC malfunction telltale behave, under FMVSS No. 136?49 CFR 571.136 (FMVSS No. 136, Electronic stability control systems for heavy vehicles), S5.4.1. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), C. Antilock Brake System, Automatic Traction Control, Electronic Stability Control and Collision Warning/Avoidance (7 of 50)
How many wheels of a truck tractor may one antilock modulator control, at most, under FMVSS No. 121?49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.1.6.1. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), C. Antilock Brake System, Automatic Traction Control, Electronic Stability Control and Collision Warning/Avoidance (7 of 50)
Over which range of vehicle speed must the ESC system of a truck tractor be operational, under FMVSS No. 136?49 CFR 571.136 (FMVSS No. 136, Electronic stability control systems for heavy vehicles), S5.2.1. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), C. Antilock Brake System, Automatic Traction Control, Electronic Stability Control and Collision Warning/Avoidance (7 of 50)
What does a wheel speed sensor usually consist of?Wikipedia, Wheel speed sensor, lead section. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), C. Antilock Brake System, Automatic Traction Control, Electronic Stability Control and Collision Warning/Avoidance (7 of 50)
What does an ABS controller look for in the wheel speed signals?Wikipedia, Anti-lock braking system, Use. Outline: ASE Medium/Heavy Truck Study Guide (2026), Brakes (Test T4), C. Antilock Brake System, Automatic Traction Control, Electronic Stability Control and Collision Warning/Avoidance (7 of 50)
How this list was compiled: Our own questions, written to the content areas of the Brakes (Test T4) test specifications and task list in the ASE Medium/Heavy Truck Study Guide (copyright 2026, https://ase.com/wp-content/uploads/ASE_MedHeavyTruck_Study_Guide.pdf, read 2026-10-14): A air brakes 32 of 50 scored questions (air supply and service systems 15, mechanical/foundation and wheel hub 13, parking brakes 4), B hydraulic brakes 11, C antilock, traction control, stability control and collision warning systems 7. The bank holds the same 15, 13, 4, 11 and 7. Every fact was read on 2026-10-14 in the public text the question names: 49 CFR 393.41, 393.43, 393.47, 393.49, 393.50, 393.53, Part 396 Appendix A, 571.105, 571.121 and 571.136 at ecfr.gov; US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, and US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 6, both in the copies at archive.org; and Wikipedia articles on air brakes, the S-cam, brake linings, brake fade, brake bleeding, parking brakes, brinelling, spalling, antilock braking, wheel speed sensors, yaw-rate sensors and collision avoidance systems. The sample questions printed in the study guide were not used. Licence: Questions, choices and explanations are original work of this site. NAVEDTRA 14050 and TM 9-8000 are works of the United States Navy and Army approved for public release, and no question or example is copied from them.
How it works
This free ASE T4 practice test asks 50 truck brake questions. For an ASE T2 and T4 practice test, T2 Diesel Engines is one link away. Unofficial, not affiliated with the National Institute for Automotive Service Excellence (ASE).
Read the full guide
What T4 covers
ASE's Medium/Heavy Truck study guide gives air brakes 32 of the 50 scored questions: air supply and service systems 15, foundation brakes and wheel hubs 13, parking brakes 4. Hydraulic brakes have 11. Antilock, traction control, stability control and collision warning systems have 7.
Where the brake answers come from
Rule questions rest on the federal brake rules in 49 CFR Parts 393, 396 and 571. Valve, booster and air-over-hydraulic questions rest on Army and Navy manuals, older than current trucks. Sensors, bearings and trailer lines rest on Wikipedia.
T2 and T4 together
T2 is Diesel Engines and T4 is Brakes: two separate tests in ASE's Medium/Heavy Truck study guide, each with its own task list. The T2 page has 60 questions of its own.
The federal rules say what a truck is built and inspected to. A maker's service information governs a repair.
Questions and answers
How many questions are on the ASE T4 test?
ASE's 2026 Medium/Heavy Truck study guide lists 60 questions for T4, 50 scored and 10 unscored, with 75 minutes to finish. Recertifying takes a 25-question test with a 30-minute limit.
Is there a free ASE T2 and T4 practice test?
Yes, as two pages. This one is T4, Brakes. The ASE certified diesel mechanic practice test covers T2, Diesel Engines. Both are free, ask for no sign-up and can be printed. Neither uses ASE's own questions.
Is this an ASE medium heavy truck T4 study guide?
It is practice built on the official one. ASE's free Medium/Heavy Truck study guide prints the T4 task list; the questions here follow its content areas, and every answer names the public source it was checked against.
Does T4 count toward Master Medium/Heavy Truck Technician?
Yes. ASE's study guide marks Brakes (T4) as required for recognition as an ASE Certified Master Medium/Heavy Truck Technician. Two years of relevant work experience are needed as well.