Five free practice questions on disc brakes: content area C of the ASE A5 Brakes test, 11 of its 45 scored questions (24.4%). 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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The left front brake of a vehicle drags and the pads are worn thin on that wheel only. With the caliper unbolted from its bracket and its bleeder screw open, the piston cannot be pushed back into its bore with a C-clamp. Which of these could be the cause?
- A caliper slide pin seized in its bore
- A brake hose with a collapsed inner liner
- A caliper piston corroded in its bore
- A master cylinder pushrod adjusted too long
Show the answer
C. Correct. With the bleeder open nothing hydraulic can hold the piston, so a piston that still will not move back is stuck in its bore, usually from corrosion after water got past the boot. The caliper is rebuilt or replaced, with new pads.
Why not the others
A. A seized slide pin can make the pads drag, but it cannot stop the piston from being pushed back once the caliper is unbolted and the bleeder is open.
B. A collapsed liner can trap pressure in the caliper, but with the bleeder open that pressure escapes, and the piston would then push back easily; this piston will not move with no pressure behind it.
D. A pushrod that is too long keeps the master cylinder from releasing, so pressure stays in every circuit and all wheels drag; with the bleeder open the piston would still push back. Here one wheel drags and the piston is stuck.
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After a caliper replacement, brake fluid seeps from both sides of the banjo fitting where the hose attaches to the caliper. The banjo bolt is at the manufacturer's torque, and the sealing faces of the bolt, hose fitting and caliper are clean and undamaged. What is the repair?
- Torque the banjo bolt past its spec
- Install new copper sealing washers
- Coat the bolt threads with sealant
- Replace the brake hose assembly
Show the answer
B. Correct. Copper banjo washers crush to seal the faces and are not reused; a washer already flattened to the old faces seldom seals again. Fit new washers and torque the bolt to the manufacturer's figure.
Why not the others
A. The bolt is already at its specified torque; tightening further can strip the caliper threads or break the bolt, and it will not seal over flattened washers.
C. A banjo fitting seals at the washer faces, not at the threads; sealant on the threads does nothing for the faces and can contaminate the fluid.
D. The seep is at the fitting faces, not along the hose; a new hose reinstalled on the same flattened washers would leak the same way.
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Each of these is good practice when new rotors are installed EXCEPT:
- measuring installed lateral runout before the wheel goes on.
- removing any oil-based rust-preventive coating.
- machining both braking surfaces as a routine step.
- cleaning rust and scale from the hub mounting face.
Show the answer
C. Correct. A new rotor is made flat and parallel, so machining it as a routine step removes service life and adds nothing. Measure installed runout first and correct only when the reading calls for it.
Why not the others
A. Installed runout includes the hub and the rotor together, so measuring it with the rotor mounted and clamped is good practice.
B. An oil-based rust preventive on a new rotor would contaminate the pads, so cleaning it off before installation is good practice; a painted or plated finish meant to stay is left on.
D. Rust or scale on the hub face tilts the rotor and adds runout, so cleaning the hub face is good practice.
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A light rattle comes from the left front over small bumps and stops whenever the brakes are applied lightly. The pads fit tightly in new abutment clips, and wheel bearing play is within specification. Which of these could be the cause?
- A pad wear indicator touching the rotor
- A loose sway bar end link
- A loose brake dust shield
- A caliper with worn slide-pin bushings
Show the answer
D. Correct. Worn bushings let the caliper body shift on its pins and knock over bumps; applying the brakes clamps the caliper to the rotor through the pads, so the rattle stops. Replace the bushings, and the pins if worn.
Why not the others
A. A wear indicator scrapes or squeals as the rotor turns, steadily with road speed; it does not make a rattle over bumps that stops with light braking.
B. A loose sway bar link rattles over bumps whether or not the brakes are applied, because braking does not clamp the link; this rattle stops with light braking.
C. A dust shield is bolted to the knuckle behind the rotor and is not clamped by the pads, so applying the brakes would not stop its rattle.
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A wheel is going back on after a brake job. Each of these is correct practice EXCEPT:
- tightening the lug nuts in a star pattern in two or more steps.
- starting each lug nut by hand before using any tool.
- oiling the stud threads, then torquing to the dry-thread spec.
- setting final torque with a torque wrench to the manufacturer's figure.
Show the answer
C. Correct. Oil or anti-seize lowers thread friction, so a dry-thread torque figure produces far more clamping force than intended and can stretch studs and distort the rotor. Install the threads in the condition the manufacturer specifies for that torque.
Why not the others
A. A star pattern in steps pulls the wheel down evenly onto the hub and rotor hat, which keeps the rotor from being distorted, so this is correct practice.
B. Starting the nuts by hand keeps them from cross-threading on the studs, so this is correct practice.
D. Final torque is set with a torque wrench to the manufacturer's figure so every nut clamps the same, so this is correct practice.
02Answer key
| Question | Answer |
|---|---|
| Q1 | C |
| Q2 | B |
| Q3 | C |
| Q4 | D |
| Q5 | C |
03What area C covers
This content area covers disc brakes and the parts they mount to: calipers, pistons, seals, slide pins and pad hardware, rotors and how they are measured, indexed and machined, pad installation and break-in, and front wheel bearings and seals. It also covers telling a brake vibration from a tire and wheel vibration on the road test.
The ASE test specification calls this content area “Disc Brake Diagnosis and Repair”. It carries 11 of the 45 scored questions, 24.4% of the test.
- Trace pulls, drag, noise and pulsation to disc faults
- Retract caliper pistons by the manufacturer's method
- Inspect calipers, slide pins, boots and mountings
- Measure rotor runout and thickness variation
- Index, machine or replace rotors
- Install and lubricate pads, then burnish them
- Diagnose and service front wheel bearings and seals
- Separate brake vibration from tire and wheel vibration
04What the questions turn on
Thickness variation and runout
Thickness variation is the largest micrometer reading minus the smallest. Lateral runout over the limit does not by itself scrap a rotor: it can be indexed on the hub or machined, as long as it stays above its machine-to thickness.
Brake shake or tire shake
A tire and wheel problem shakes whenever the vehicle is at that speed. A rotor problem shakes only when the pads clamp the rotor. A shake at highway speed that starts or grows with light braking points to the brakes.
Rubber-safe grease only
General-purpose petroleum grease swells the rubber bushings and boots on caliper slide pins, so the pins bind and the caliper drags. The repair is new rubber parts and the high-temperature, rubber-safe grease the manufacturer specifies.
Uneven lug nut torque
Lug nuts tightened to widely different torques clamp the rotor hat unevenly and distort it. Runout grows, the rotor brushes the pads each turn, and thickness variation and pedal pulsation follow. The nuts are tightened in a star pattern with a torque wrench.
05The other content areas
The A5 test has four content areas. Each has its own page of free questions:
The ASE A5 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.
ToolboxPrep is an independent study site. It is not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original practice questions written to the published ASE test specifications; they are not actual test questions.