• 50 questions

ASE H4 Transit Bus Brakes Practice Test

Unofficial practice for ASE's H4 Brakes test: air supply, foundation brakes, parking brakes and wheel bearings on a transit bus.

A four-way protection valve feeds the primary and secondary reservoirs. Which brakes does the primary reservoir serve?

Pick an answer, then press Check answer. Then you see Correct or Not quite, with the reason. Keys: A to D pick, Enter checks.

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Exam mode: 50 questions, 75 minutes.

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Unofficial practice questions, not affiliated with the National Institute for Automotive Service Excellence (ASE). Bank checked October 13, 2026.

Next step The federal air brake rules: CDL air brakes practiceAll eight H tests: transit bus practice

All 50 questions

Air supply and service systems 24

  • A bus has exactly the reservoir capacity FMVSS No. 121 requires. Within what time must its compressor raise reservoir pressure from 85 to 100 psi at maximum recommended engine speed? 49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.1.1, Air compressor. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • A drive wheel spins on a wet street. Which of these is an intervention a traction control system may make? Wikipedia, Traction control system, lead section. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • A four-way protection valve feeds the primary and secondary reservoirs. Which brakes does the primary reservoir serve? Wikipedia, Air brake (road vehicle), Supply system. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
Show all 50 questions (47 more)

Air supply and service systems, continued

  • A leak is too small to hear. How does the Navy manual find it? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 6, Inspecting and Troubleshooting Brake Systems, Troubleshooting Air Brake Systems. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • A one-way check valve is tested on the bench. What is its cracking pressure? Wikipedia, Check valve, lead section. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • A replacement air reservoir is chosen for a bus whose compressor cuts out at 125 psi. What internal hydrostatic pressure must a reservoir withstand for 10 minutes under FMVSS No. 121? 49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.1.2.2. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • All brakes release too slowly after the pedal is let up, and shoe clearance is correct. Which valve does the Navy air brake chart list as a cause? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 6, Inspecting and Troubleshooting Brake Systems, Troubleshooting Air Brake Systems, table 6-3. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • The brake pedal starts down. Inside the brake valve, which happens first? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • The driver holds the brake pedal steady partway down. What is the brake valve doing in this holding position? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • The engine drives the air compressor of an air brake system. In which two ways? Wikipedia, Air brake (road vehicle), Supply system. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • The governor in TM 9-8000 senses reservoir pressure with a bent metal tube that tries to unbend as the pressure inside it rises. What is this principle called? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • How is the air compressor of an air brake system lubricated, 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 Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • In the Navy manual's air buildup test, the reservoirs are drained and the engine started. What result calls for a check of leaks, compressor and relief valves? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 6, Inspecting and Troubleshooting Brake Systems, Troubleshooting Air Brake Systems. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • Reservoir pressure has dropped far enough for the governor to cut in. What does the governor do with the air that was holding the compressor unloaded? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • Some older air brake systems have a wig wag. What does it do? Wikipedia, Air brake (road vehicle), Wig wag. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • Under the brake actuation time test of FMVSS No. 121, how soon must each brake chamber of a bus reach 60 psi after the pedal first moves? 49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.3.3, Brake actuation time. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • Under the brake release time test of FMVSS No. 121, a bus brake chamber starts at 95 psi. How soon must it fall to 5 psi after the pedal first moves? 49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.3.4, Brake release time. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • What does a defective air dryer lead to in cold locations? Wikipedia, Air brake (road vehicle), Disadvantages. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • Which wheels must the antilock system of an air-braked bus built since March 1, 1998 control directly under FMVSS No. 121? 49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.1.6.1(a). Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • Why are the service brakes split into front and rear circuits, each with its own supply reservoir? Wikipedia, Air brake (road vehicle), Control system. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • Why can a retarder usually not bring a bus to a standstill by itself? Wikipedia, Retarder (mechanical engineering), lead section. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • Why does a relay valve react quickly to small changes in pressure from the brake valve? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • Why does compressed air always carry water into an air system? Wikipedia, Air dryer, Applications. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)
  • Why is the supply reservoir, the one closest to the compressor, also called the wet tank? Wikipedia, Air brake (road vehicle), Supply system. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), A. Air Supply and Service Systems Diagnosis and Repair (24 of 50)

Mechanical and foundation brakes 14

  • As the linings of an S-cam brake wear, what happens at the cam? Wikipedia, S-cam, How it works. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • The brakes grab when the pedal is pressed. Which drum fault does the Navy air brake chart list as a cause? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 6, Inspecting and Troubleshooting Brake Systems, Troubleshooting Air Brake Systems, table 6-3. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • How do cast iron brake drums compare with steel drums, by TM 9-8000? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-7, Construction. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • How is a slack adjuster connected to the brake camshaft? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • On a manual slack adjuster, what does turning the adjusting screw do? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-39, System Components. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • One brake drags with the pedal released because its shoe binds on the anchor pin. What remedy does the Navy air brake chart give? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 6, Inspecting and Troubleshooting Brake Systems, Troubleshooting Air Brake Systems, table 6-3. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • What are the fins or ribs on the outside of a brake drum for? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-7, Construction. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • What does the S-cam design allow the bulky air cylinders to do? Wikipedia, S-cam, lead section. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • What does TM 9-8000 say about metallic brake linings? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-7, Construction. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • What is a ventilated brake rotor? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-13. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • Which finding on a brake spider fails the structural parts standard of 49 CFR 570.59? 49 CFR 570.59, paragraph (d), Structural and mechanical parts. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • Why are brass rivets chosen to attach brake lining to a shoe, by TM 9-8000? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-7, Construction. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • Why do steel brake shoes hold their clearance to the drum as the brake heats up, by TM 9-8000? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-7, Construction. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)
  • Why does a drum brake lose stopping power when repeated stops overheat it, by TM 9-8000? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, Braking Systems, paragraph 34-11, Disadvantages. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), B. Mechanical/Foundation Brakes Diagnosis and Repair (14 of 50)

Parking brakes 7

  • A service brake chamber diaphragm on another brake system has ruptured. Must the parking brakes of a bus still meet their minimum performance under FMVSS No. 121? 49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.6.3.1. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), C. Parking Brakes Diagnosis and Repair (7 of 50)
  • A supply line fails and all air is lost at once from the spring brake chambers. What happens? Wikipedia, Air brake (road vehicle), Design and function. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), C. Parking Brakes Diagnosis and Repair (7 of 50)
  • The driver sets the parking brake on an air-braked bus. What happens to the air that was holding the spring brakes off? Wikipedia, Air brake (road vehicle), Design and function. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), C. Parking Brakes Diagnosis and Repair (7 of 50)
  • In the grade holding test of FMVSS No. 121, on what grade must the parking brakes hold the bus still, facing uphill and downhill? 49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.6.2, Grade holding. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), C. Parking Brakes Diagnosis and Repair (7 of 50)
  • In the static drawbar pull test of FMVSS No. 121, the parking brake force of a two-axle bus is divided by the axle's gross axle weight rating. What is the least the result may be on the rear axle? 49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.6.1, Static retardation force. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), C. Parking Brakes Diagnosis and Repair (7 of 50)
  • In the stored energy test of FMVSS No. 121, the engine is turned off and a leak is introduced. Which parking brake control sequence follows? 49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.6.6.3. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), C. Parking Brakes Diagnosis and Repair (7 of 50)
  • Within what time of the parking brake control being actuated must the mechanical means that holds the brakes be actuated on a bus, under FMVSS No. 121? 49 CFR 571.121 (FMVSS No. 121, Air brake systems), S5.6.3.3. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), C. Parking Brakes Diagnosis and Repair (7 of 50)

Wheel bearings 5

  • A bearing race shows imprints that look like dents, though the bearing took no impact. It sat loaded under small vibrations. What is this damage called? Wikipedia, False brinelling, lead section. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), D. Wheel Bearings Diagnosis and Repair (5 of 50)
  • A bus pulls to one side when the brakes are applied. Which wheel bearing fault is on the Navy manual's list of causes? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 12, Wheel and Track Alignment, steering and alignment complaints. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), D. Wheel Bearings Diagnosis and Repair (5 of 50)
  • A sealed wheel hub assembly is being replaced. How is the new one tightened? Wikipedia, Wheel hub assembly, Operation. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), D. Wheel Bearings Diagnosis and Repair (5 of 50)
  • Which loads can a tapered roller bearing support? Wikipedia, Tapered roller bearing, lead section. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), D. Wheel Bearings Diagnosis and Repair (5 of 50)
  • Why are tapered roller bearings often used in back-to-back pairs? Wikipedia, Tapered roller bearing, Applications. Outline: ASE Transit Bus Study Guide (2026), Brakes (Test H4), D. Wheel Bearings Diagnosis and Repair (5 of 50)

How this list was compiled: Our own questions, written to the four content areas of the Brakes (Test H4) test specifications and task list in the ASE Transit Bus Study Guide (copyright 2026, https://ase.com/wp-content/uploads/ASE_TransitBus_Study_Guide.pdf, read 2026-10-13): air supply and service systems 24 of 50 scored questions, mechanical/foundation brakes 14, parking brakes 7, wheel bearings 5. The bank holds the same 24, 14, 7 and 5. Every fact was read on 2026-10-13 in the public text the question names: 49 CFR 571.121 (FMVSS No. 121) and 49 CFR 570.59 at ecfr.gov; US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, and US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapters 6 and 12, both in the copies at archive.org; and Wikipedia articles on air brakes, air dryers, check valves, the S-cam, traction control, retarders, tapered roller bearings, false brinelling and wheel hub assemblies. 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 H4 transit bus brakes practice test asks 50 questions, as many as the real test scores. It is unofficial and not affiliated with the National Institute for Automotive Service Excellence (ASE).

Read the full guide

Air supply is nearly half of H4

ASE's Transit Bus study guide gives air supply and service systems 24 of the 50 scored questions. Mechanical and foundation brakes have 14, parking brakes 7 and wheel bearings 5. H4 has no content area for hydraulic brakes.

Where the brake answers come from

Governor, brake valve, relay valve and slack adjuster questions rest on Army and Navy manuals, older than current buses. Timing and parking brake figures come from FMVSS No. 121. Air dryer, traction control and most bearing questions rest on Wikipedia.

  • FMVSS No. 121 says what a new air-braked bus is built to. A maker's service manual governs a repair.
  • Learn each valve by its job: the relay valve speeds application, the quick-release valve speeds release.

Questions and answers

How many questions are on the ASE H4 test?

ASE's 2026 Transit Bus study guide lists 60 questions for H4, 50 scored and 10 unscored, with 75 minutes to finish. Recertification is a shorter test of 25 questions in 30 minutes.

Are these real ASE H4 questions?

No. Each one was written here from the H4 task list and a public source that the question names. None is taken from the H4 test or from the seven sample questions ASE prints for it.

Is H4 required for Master Transit Bus Technician status?

Yes. ASE's study guide stars H3 through H8, H4 among them. A technician needs all six, plus either H1 or H2, for Master Transit Bus Technician status.

How is H4 different from the truck brakes test, T4?

ASE's Medium/Heavy Truck study guide gives T4 11 hydraulic brake questions and 7 on antilock, traction and stability systems among its 50. H4 has no hydraulic area, and wheel bearings are an area of their own.

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