hydraulic system diagnostics and repair questions and answers

what is the switch in the center of this cutaway hydraulic brake component?

pressure differential switch

Two technicians are discussing master cylinders. Technician A says that it is normal to see fluid movement in the reservoir when the brake pedal is depressed. Technician B says a defective master cylinder can cause the brake pedal to slowly sink to the floor when depressed. Which technician is correct?

both A and B

The primary brake circuit fails due to a leak in the lines leaving the rear section of a dual-split master cylinder. Technician A says that the driver will notice a lower-than-normal brake pedal and some reduced braking power. Technician B says that the brake pedal will "grab" higher than normal. Which technician is correct?

A only

Two technicians are discussing a problem where the brake pedal travels too far before the vehicle starts to slow. Technician A says that the brake pedal linkage may be out of adjustment. Technician B says that one circuit from the master cylinder may be leaking or defective. Which technician is correct?

Both A and B

The rear brakes lock up during a regular brake application. Technician A says a stuck open metering valve could be the cause. Technician B says that stuck front disc brake calipers could be the cause.

Which technician is correct?

B only

A lower-than-normal and spongy brake pedal is being diagnosed. Technician A says that air in the hydraulic system could be the cause. Technician B says a defective pressure differential switch could be the cause. Which technician is correct?

A only

The button on the valve should be depressed or held out when pressure bleeding the brakes.

metering

Most vehicle manufacturers specify brake fluid that meets what specification?

either A or B

Two technicians are discussing the reason that the brake fluid level in the master cylinder drops after several months of driving. Technician A says that it may be normal due to the wear of the disc brake pads. Technician B says that a low brake fluid level may indicate a hydraulic leak somewhere in the system. Which technician is correct?

Both A and B

Two technicians are discussing brake fluid. Technician A says that brake fluid should only be used from a sealed container because it absorbs moisture from the air. Technician B says that brake fluid should be handled with care because it can remove paint from the vehicle if spilled. Which technician is correct?

Both A and B

If automatic transmission fluid or power steering fluid gets into a master cylinder, all of the rubber parts must be replaced because

the rubber seals will swell and cause brake failure

Two technicians are discussing brake lines. Technician A says that a double lap flare end can be used when replacing a line that came from the factory with an ISO flare. Technician B says that a replacement line with an ISO flare can be used to replace a line that came from the factory with a double ap flare end. Which technician is correct?

neither A nor B

The brake bleeding procedure usually specifled

RR, LR, RF, LF

What should be used to replace a leaking brake line?

Either a or c

Most manufacturers recommend that disassembled brake parts should be cleaned with

denatured alcohol

A customer complains that the brake pedal is lower than normal. Technician A says that the vacuum power brake booster may be defective. Technician B says that air in the hydraulic system could be the cause. Which technician is correct?

B only

The rubber used in most brake system components will swell if exposed to

engine oil or ATF

Technician A says brake fluid should be filled to the top of the reservoir to be assured of proper brake pressure when the brakes are applied. Technician B says that the brake fluid level should be filled only to the maximum-level line to allow for expansion when the brake fluid gets hot during normal operation. Which technician is correct?

B only

Self-apply of the brakes can occur if

the vent port (compensating port) is clogged or covered

Technician A says that the brake pedal height should be checked as part of a thorough visual inspec-ton of the brake system. Technician B says the pedal free play and pedal reserve should be checked. Which technician is correct?

Both a and b

Technician A says the red brake warning lamp on the dash will light if there is a hydraulic failure or low brake fluid level. Technician B says the red brake warning lamp on the dash will light if the parking brake is on. Which technician is correct?

Both A and B

A vehicle tends to lock up the front wheels when being driven on slippery road surfaces. Technician A says that the metering valve may be defective. Technician B says the proportioning valve may be struck open. Which technician is correct?

A only

Two technicians are discussing bleeding air from the brake hydraulic system. Tech A says to depress the brake pedal slowly and not allow pedal to go to the floor to prevent possible seal damage inside the master cylinder. Tech B says to wait 15 seconds between strokes of the brake pads. Which tech is correct?

Both A and B

The brakes were found to be dragging on the right front on a rear-wheel drive vehicle equipped with front disc brakes and drum rear brakes. What is the most likely cause?

stuck caliper slides

Technician A says that the bleeder valve should be opened before pushing the caliper piston back into the caliper during disc brake service. Technician B says to use a brake hose clamp on the brake line as the piston is pushed into the caliper during disc brake service. Which technician is correct?

A only

An import vehicle is in the shop for a brake fluid replacement as recommended by the manufacturer. Technician A says that all that is required is to suction the old fluid out of the master cylinder reservoir and replace with new fluid. Technician B says that all of the bleeders should be opened and the brake fluid bled until only fresh fluid is seen. Which technician is correct?

B only

Two technicians are discussing the installation of a new master cylinder. Technician A says that the master cylinder should be bled on the bench before being installed on the vehicle. Technician B says that a new or rebuilt master cylinder is already fitted with brake fluid and ready to install on the vehicle. Which technician is correct?

A only

The special tool shown is used to

hold the metering valve open

A replacement vacuum brake booster and master cylinder was installed and then durino a test drive, the brakes self-applied after about 10 minutes of driving. Technician A says that the brake pedal linkage may be incorrectly adjusted or the wrong parts were installed that has caused the vent port (compensating port) to be blocked. Technician B says the master cylinder reservoir may have been overfilled. Which technician is correct?

Both A and B

Which of the following conditions can cause the red brake warning lamp to light?

1. Low brake fluid level in the master cylinder reservoir

2. Parking brake applied

3. A leak in either the front or rear brake line

4. All of the above

The front of the vehicle dips downward in the front during light braking. Which of the following is the most likely cause?

A defective metering valve

Brake fluid is observed leaking from the rear of the master cylinder and flowing down the front of the vacuum brake booster assembly. Which fault is the most likely?

A leaking secondary seal on the primary piston of the master cylinder

The owner of a sport utility vehicle (SUV) complains that the brake pedal drops when the brake pedal is depressed while stopped at a traffic light. The brakes seem to operate normally and no external fluid leaks can be seen. Technician A says that the metering or proportioning valve may be defective. Technician B says that the master cylinder may be leaking internally due to a failed seals). Which technician is correct?

B only

What is the puroose of the two units that are located under this front-wheel-drive vehicle?

Rear proportioning valves to limit rear wheel lockup

The brake lines from the master cylinder are being replaced because they were damaged in a collision. Technician A says that the replacement lines should be colled like the factory original to help increase brake pressure to the rear brakes. Technician B says the coils are to help reduce vibration and to allow the brake line to move slightly as the body moves on the frame. Which technician is correct?

B only

What is this brake hydraulic component?

A combination valve

What is the most likely service being performed?

Bleeding the air from the disc brake caliper and line

Brake fluid is discovered on the sidewall of the rear tire as shown.What is the most likely cause?

Leaking rear wheel cylinder

Two technicians are discussing the system in the illustration.Technician A says that this valve helps reduce rear wheel lockup during hard braking. Technician B says that the lever should be disconnected to bleed the rear brakes. Which technician is correct?

A only

Two technicians are discussing using the equipment shown. Technician A says that the pressure exerted on the master cylinder should be less than about 20 psi (138 kPa). Technician B says that a button on the metering valve may need to be opened to allow bleeding of the front brakes.

Both A and B

The right front wheel brake line on a front-wheel-drive vehicle is cut by road debris. Which other wheel brake may be affected?

the left rear

Two technicians are discussing manual brake bleeding. Technician A says that an assistant should apply as much force as possible on the brake pedal to force the air and the brake fluid out of the bleeder valves. Technician B says that the assistant should pumo the brake pedal rapidly before bleeding to force the air toward the bleeder valves. Which technician is correct?

Neither A nor B

Two technicians are discussing gravity bleeding. Technician A says that gravity bleeding of disc brakes can be achieved by opening the bleeder valve(s) and waiting until clear brake fluid without bubbles is observed flowing out of the valve, then closing the valve. Technician B says that if the bleeder valve is opened, air will get into the brake system unless the brake pedal is depressed. Which technician is correct?

A only

Technician A says a pull to the right during braking could be caused by a defective metering valve Technician B says a pull to the left could be caused by a defective proportioning valve. Which technician is correct?

neither A nor B

The rear brake lights do not work when the brake pedal is depressed. Technician A says that low brake fluid in the master cylinder can be the cause. Technician B says that an open in the wiring to the brake lights could be the cause. Which technician is correct?

B only

The red brake warning light on the dash is on and the parking brake is fully released. Technician A says that the brake fluid may be low in the master cylinder. Technician B says that the rear brake linings may be worn to the limit where replacement is necessary. Which technician is correct?

A only

Technician A says that a restricted flexible brake hose can cause a low brake pedal. Technician B says air in the brake lines can cause a low brake pedal. Which technician is correct?

B only

A driver has to "pump up" the brakes (depress the brake pedal several times) before the vehicle starts to slow down. Technician A says that the rear drum brakes may need replacing or adjusting.Technician B says that loose front wheel bearings could be the cause. Which technician is correct?

Both A and B

A Hydro-Boost hydraulic brake booster is being diagnosed.Technician A says that if the accumulator is loose and can be moved by hand with the engine off, then it has lost its charge and must be replaced. Technician B says it is normal to lose power-assisted brakes as soon as the engine stops on a vehicle equipped with Hydro-Boost. Which technician is correct?

A only

A vehicle equipped with a vacuum brake booster has no power assist until the engine has run for a minute or two, then the power assist works normally. What is the most likely cause?

A defective check valve

Technician A says that a defective vacuum brake booster can cause a lower-than-normal brake pedal during normal braking. Technician B says that worn or misadjusted rear drum brakes can cause a lower-than-normal brake pedal during normal braking. Which technician is correct?

B only

A brake pedal pulsation complaint is being diagnosed on a vehicle equipped with a Hydro-Boost brake-assist system. Technician A says the pulsation could be caused by a loose power steering pump belt. Technician B says that a defective (warped) front disc brake rotor could be the cause.Which technician is correct?

B only

The first step in diagnosing a Hydro-Boost problem is

a thorough visual inspection

A brake pedal feels spongy when depressed. Technician A says that a defective hydraulic brake booster could be the cause. Technician B says that a defective vacuum brake booster could be thecause. Which technician is correct?

neither A nor B

A defective vacuum brake booster will cause a

hard break pedal

Two technicians are discussing the testing of a vacuum brake booster. Technician A says to check the operation of a vacuum brake booster, the brake pedal should be depressed until the assist is depleted and then the engine should be started and then checked for a high brake pedal. Technician B says the booster should be depleted and the brake pedal should drop when the engine starts if the booster is okay. Which tech is correct?

B only

Two technicians are discussing vacuum brake boosters. Technician A says a low, soft brake pedal is an indication of a defective booster. Technician B says that there should be at least assisted brake applications if the engine stops running. Which technician is correct?

B only