Five free practice questions on hydraulic brakes: content area B of the ASE T4 Brakes test, 11 of its 50 scored questions (22%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.
01The questions
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A medium-duty truck's hydraulic booster has lost both its steering-pump flow and its electric backup pump. How can the driver still apply the brakes?
- Through the booster mechanically, with very high pedal effort
- Only by the parking brake, as the pedal has no apply path
- By spring brakes that apply when booster pressure falls
- Through the booster mechanically, with near-normal pedal effort
Show the answer
A. Correct. The booster has a mechanical push-through: the pedal rod can drive the power piston and the master cylinder pistons with no hydraulic assist. It takes very high pedal effort and gives poor control, so the truck is moved only to get it off the road.
Why not the others
B. The pedal still has a mechanical path: the booster's push-through lets the pedal rod drive the master cylinder pistons with no assist. The parking brake is not the only way left to stop, though the service brakes now take very high pedal effort.
C. Spring brakes belong to air brake systems; a hydraulic booster does not apply them when its pressure falls. On this system the pedal can still push mechanically through the booster to the master cylinder, though with very high effort.
D. The mechanical push-through does work with both assist sources lost, but without any hydraulic assist the pedal effort is very high, not near normal, and control is poor. The truck is moved only to get it off the road.
ID T4-B-005 · Task T4-B-18 (ASE task list)
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A truck's brake pedal is firm but travels well down before the brakes begin to apply. The manufacturer specifies 0.25 to 0.50 in. of pedal free play, set by the length of the threaded pushrod between the pedal and the booster; it measures 1.10 in. What should be done?
- Replace the master cylinder for internal bypass
- Shorten the pushrod until free play is in range
- Bleed the system to purge air from the brake lines
- Lengthen the pushrod until free play is in range
Show the answer
D. Correct. Free play is the pedal travel before the pushrod starts to move the booster input, and 1.10 in. is 0.60 in. over the 0.50 in. maximum. Lengthening the pushrod takes up the extra travel; set it within 0.25 to 0.50 in., lock the adjuster and recheck.
Why not the others
A. An internally bypassing master cylinder lets the pedal sink under steady pressure; here the pedal is firm and the extra travel is measured free play. Correcting the pushrod length cures it.
B. Shortening the pushrod would add free play and make the 1.10 in. reading worse. The pushrod is lengthened to bring free play down into the 0.25 to 0.50 in. range.
C. Air would make the pedal spongy, but this pedal is firm; its extra travel happens before anything is pushed, which is free play. The pushrod length is corrected instead.
ID T4-B-014 · Task T4-B-3 (ASE task list)
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Many medium-duty trucks with disc brakes at all four wheels have no metering (hold-off) valve. Why is one not needed?
- Disc brakes self-energize and need less pressure
- The proportioning valve does the hold-off job
- The master cylinder applies its circuits in turn
- Front and rear calipers start applying together
Show the answer
D. Correct. A metering valve holds off the front calipers until rear drum shoes overcome their return springs and reach the drums. Rear calipers have no return springs to overcome and apply as soon as pressure rises, so front and rear brakes start together without one.
Why not the others
A. Disc brakes are not self-energizing, which is why they need high line pressure, and that has nothing to do with a metering valve. It is omitted because rear calipers apply at the same time as the fronts.
B. A proportioning valve reduces rear pressure above its split point in harder stops; it never delays front pressure. No hold-off is needed because rear calipers have no return springs and apply as soon as pressure rises, together with the fronts.
C. A tandem master cylinder pressurizes both circuits together, not one after the other. The metering valve is left out because rear calipers apply as quickly as the fronts.
ID T4-B-019 · Task T4-B-6 (ASE task list)
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A truck's master cylinder cap calls for DOT 3 brake fluid, and the shop has a bottle of DOT 5.1 fluid. Technician A says DOT 5.1 is silicone-based like DOT 5. Technician B says DOT 5.1, like DOT 3, absorbs moisture from the air. Who is right?
- A only
- B only
- Both A and B
- Neither A nor B
Show the answer
B. Correct. Technician B is right: DOT 3, DOT 4 and DOT 5.1 are glycol-based fluids that absorb moisture, which lowers their boiling point over time. Technician A is wrong, because only DOT 5 is silicone-based and DOT 5.1 is labeled non-silicone base. The fluid named on the cap is still the one to use.
Why not the others
A. Technician A is wrong: DOT 5.1 is a non-silicone fluid, and federal labeling rules require DOT 5.1 containers to say so; only DOT 5 is silicone-based. Technician B is right that DOT 5.1, like DOT 3, is glycol-based and absorbs moisture.
C. Only Technician B is right. Technician A has the grades confused: DOT 5 is silicone-based, while DOT 5.1 is a glycol-based, non-silicone fluid that absorbs moisture as DOT 3 does.
D. Technician B is right, since DOT 5.1 is glycol-based and absorbs moisture as DOT 3 does. Technician A is the one who is wrong: DOT 5.1 is not silicone, and only DOT 5 is.
ID T4-B-025 · Task T4-B-10 (ASE task list) · FMVSS 116
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During stops, the driver of a truck with front discs and rear drums feels the brake pedal pulse up and down. Which of these is LEAST likely to produce the pulsation?
- Glazed linings on the front pads
- An out-of-round rear brake drum
- Front rotor thickness variation
- A rear drum distorted by uneven lug torque
Show the answer
A. Correct. Glazing lowers the pads' friction evenly all the way around the rotor, so it raises pedal effort but does not make the pedal pulse. Pulsation comes from something that varies once per revolution, such as thickness variation or an out-of-round drum.
Why not the others
B. This can produce it: as an out-of-round drum turns, the shoes are pushed in and out once per revolution, and the wheel cylinder pistons pass that to the pedal.
C. This can produce it: thickness variation pushes the caliper pistons back and forth as the rotor turns, which the driver feels as pedal pulsation.
D. This can produce it: uneven lug nut torque can distort a drum out of round, which pulses the pedal through the wheel cylinder. Lug nuts are torqued evenly to the manufacturer's specification.
ID T4-B-031 · Task T4-B-11 (ASE task list)
02Answer key
| Question | Answer |
|---|---|
| Q1 | A |
| Q2 | D |
| Q3 | D |
| Q4 | B |
| Q5 | A |
03What area B covers
Medium-duty trucks with hydraulic brakes are the subject here. The area takes in the master cylinder, lines, valves, wheel cylinders, calipers and fluid, then the drums, rotors, shoes and pads at the wheels. It also covers driveline and lever-type parking brakes, hydraulic boosters fed by the steering pump along with their electric backup pumps, and the warning, indicator and stop lamp circuits.
The ASE test specification calls this content area “Hydraulic Brakes Diagnosis and Repair”. It carries 11 of the 50 scored questions, 22% of the test.
- Trace low pedal, pulls, drag and noise to causes
- Adjust pedal free play; test and replace master cylinders
- Route and secure lines and hoses; test proportioning valves
- Test brake fluid, then bleed or flush the system
- Service wheel cylinders, calipers, shoes, pads and hardware
- Measure drums and rotors against their limits
- Adjust driveline and lever-operated parking brakes
- Test hydraulic boosters, backup pumps and lamp circuits
04What the questions turn on
Booster fluid and the backup pump
A hydraulic booster runs on the power steering fluid the maker specifies. With the engine off, key on and pedal applied, the backup pump should run and light its lamp. Weak assist while it runs can mean fluid escaping past the inlet check valve.
A low pedal that pumps up
A low pedal comes from extra fluid volume at the wheels, compressible air, or fluid slipping past a cup. A pedal that comes up high and firm after two pumps, with no air found, points to self-adjusters that are not taking up shoe clearance.
What a driveline parking brake holds
A drum brake on the transmission output holds only the driveshaft, and axle gearing multiplies its holding torque, so it can be small. With an open differential and one drive wheel raised, it cannot keep the truck from rolling, so the wheels are chocked.
Telling the fluids apart
DOT 3, DOT 4 and DOT 5.1 are glycol fluids that absorb moisture; only DOT 5 is silicone. Water sorts out a wet wheel: glycol brake fluid dissolves in it, while gear oil beads up or floats. The fluid named on the cap is used.
05The other content areas
The T4 test has three content areas. Each has its own page of free questions:
The ASE T4 Brakes practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.
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