Question 1

Technician A says the rear or back of the booster is that part nearest the driver and abuts the bulkhead. Technician B says the front or forward part of the booster is where the master cylinder is installed. Who is correct?

Accepted Answer

Both technicians are correct in describing opposite ends of the brake booster. Technician A is referring to the bulkhead or firewall side while Technician B is describing the side where the master cylinder is installed. Therefore, both statements are correct.

Question 2

A vehicle has power assist during engine operation, but it has no assist after the engine has been off and during initial engine startup. Technician A says a stuck close vacuum check valve could be the cause. Technician B says a leaking vacuum check valve could be the cause. Who is correct?

Accepted Answer

If the power assist is not working during initial engine startup or after the engine has been turned off, it indicates a vacuum leak in the brake booster or its associated components. Technician B is correct that a leaking vacuum check valve could be the cause. Technician A's suggestion that a stuck close vacuum check valve could be the cause is incorrect as a stuck closed check valve would not allow the vacuum to escape and thus there would be no loss of power assist.

Question 3

Technician A says pedal free play is the first easy movement of the brake pedal before the braking action begins to engage. Technician B says pedal free play should only be about 1/16 to 3/16 on most cases. Who is correct?

Accepted Answer

Technician A is correct in defining pedal free play and Technician B is correct in specifying the appropriate amount of pedal free play. Therefore, both technicians are correct.

Question 4

Vacuum power brakes are being discussed. Technician A says vacuum on both sides of the diaphragm doubles the amount of force on the master cylinder pistons. Technician B says the return spring forces the diaphragm to the forward position when there is vacuum on both sides of the diaphragm. Who is correct?

Accepted Answer

Vacuum on both sides of the diaphragm does not double the force; it neutralizes the force, and the return spring does not move the diaphragm forward when vacuum is equal on both sides.

Question 5

Technician A says to diagnose a brake system that does not release, loosen the connection between the master cylinder and the brake booster. Technician B says if the brakes do not release when the master cylinder is removed from the booster, the booster is defective. Who is correct?

Accepted Answer

Technician A is correct because loosening the connection between the master cylinder and the brake booster can help determine if the problem is due to a blocked brake line or a malfunctioning brake booster. Technician B is incorrect because a defective master cylinder can also cause the brakes not to release, not just a defective booster.

Question 6

Electrohydraulic brakes are being discussed. Technician A says an electrohydraulic brake system controls hydraulic braking action through the use of electrical solenoids. Technician B says the system shares information with ABS, TCS, and electronic suspension. Who is correct?

Accepted Answer

Both technicians are correct. Electrohydraulic brake systems do use electrical solenoids to control hydraulic braking and they often share information with other electronic systems such as ABS, TCS, and electronic suspension.

Question 7

Technician A says the tool shown is used to adjust the booster's vacuum valve. Technician B says the tool is used to set the depth of the booster's diaphragm. Who is correct?

Accepted Answer

The answer of Technician A says the tool shown is...

Question 8

All of the following statements about hydro-boost system accumulators are true EXCEPT:

Accepted Answer

Accumulators are pressurized continuously as the pump operates, not just when pump flow stops.

Question 9

Technician A says, with the brakes off, the pressure in the front chamber helps hold the diaphragm in the released position. Technician B says air pressure in the rear chamber counteracts the opposing vacuum to hold the diaphragm in the released position. Who is correct?

Accepted Answer

In a typical brake system, the diaphragm is held in the released position by a spring, not by air pressure in either chamber.

Question 10

Technician A says a hydraulic brake booster is usually found on vehicles with diesel engines. Technician B says most passenger cars and light trucks use the hydro-boost system. Who is correct?

Accepted Answer

Hydraulic brake boosters, also known as hydro-boost systems, are indeed more commonly found on vehicles with diesel engines because diesel engines do not produce vacuum, which is required for traditional vacuum brake boosters. Most passenger cars and light trucks use vacuum brake boosters instead of hydro-boost systems.

Question 11

Technician A says the air and vacuum valves used on a tandem diaphragm must control vacuum and atmospheric pressure on two diaphragms at the same time. Technician B says when the brakes on a tandem diaphragm system are released, there is a vacuum on both sides of each diaphragm. Who is correct?

Accepted Answer

Both technicians are correct. Technician A is correct in stating that the air and vacuum valves must control both vacuum and atmospheric pressure simultaneously on two diaphragms in a tandem diaphragm system. Technician B is correct in stating that when the brakes are released in such a system, there is a vacuum present on both sides of each diaphragm, which is how the system returns to its default state.

Question 12

Technician A says all vacuum boosters are single-diaphragm units. Technician B says vacuum boosters can have one or two diaphragms, and single-diaphragm boosters are smaller in diameter than dual-diameter diaphragm vacuum boosters . Who is correct?

Accepted Answer

The answer of Technician A says all vacuum boosters are...

Question 13

Technician A says hydro-boost operation can be divided into three stages. Technician B says that moderate brake application causes the input pushrod to press on the reaction rod in the end of the power piston. Who is correct?

Accepted Answer

The answer of Technician A says hydro-boost operation can be...

Question 14

Technician A says lever-type vacuum power-assist brake system gives the driver a "feel" for the braking effort. Technician B says this "feel" is similar to that of a nonpower boost brake system. Who is correct?

Accepted Answer

Both technicians are correct. The lever-type vacuum power-assist brake system gives the driver a "feel" for the braking effort similar to that of a nonpower boost brake system.

Question 15

Technician A says a hydraulic power booster unit is installed in the same place as a vacuum booster. Technician B says the function of the hydraulic power booster is to multiply the force of the driver's foot on the brake pedal. Who is correct?

Accepted Answer

Both technicians are correct. Technician A is correct in stating that a hydraulic power booster unit is typically installed in the same location as a vacuum booster, which is between the brake pedal and the master cylinder. Technician B is correct in stating that the function of the hydraulic power booster is to multiply the force applied by the driver's foot on the brake pedal, thereby assisting in applying the brakes more effectively.

Question 16

Technician A says a restricted vacuum feed hose may cause loss of assist after several quick brake applications. Technician B says brake fluid in the vacuum feed hose indicates a leaking master cylinder seal. Who is correct?

Accepted Answer

Both technicians are correct. A restricted vacuum feed hose can cause loss of assist after several quick brake applications because the vacuum supply to the brake booster is decreased, resulting in reduced power assist. Brake fluid in the vacuum feed hose indicates a leaking master cylinder seal because the brake fluid has leaked past the seal and into the vacuum lines connected to the brake booster.

Question 17

On a vacuum-boosted system, all of the following can cause poor power-assist unit operation EXCEPT:

Accepted Answer

Excessive manifold vacuum would actually improve power-assist unit operation on a vacuum-boosted system. Leaking or collapsed vacuum lines, punctured diaphragm, and leaky piston seals can all cause poor power-assist unit operation.

Question 18

Technician A says vacuum for most power brake systems is supplied by the engine intake manifold. Technician B says many late-model cars that use intake manifold vacuum as the power source for the power brakes have a vacuum reservoir. Who is correct?

Accepted Answer

Both technicians are correct. In most power brake systems, vacuum is supplied by the engine intake manifold. However, many late-model cars that use this as the power source for the power brakes have a vacuum reservoir to ensure consistent vacuum supply even during times when the engine is not producing enough vacuum, such as during hard acceleration or when the engine is idling.

Question 19

Technician A says a ir fills the rear chamber when brake application opens the air valve and closes the vacuum valve, and the front chamber is kept in vacuum . Technician B says w hen the brakes are held at midpoint, both valves are closed to trap vacuum and atmospheric pressure and keep the diaphragm in a balanced position . Who is correct?

Accepted Answer

Both Technician A and Technician B are correct. Technician A describes the process of how air fills the rear chamber to apply the brakes, while Technician B explains the mechanism for holding the brakes at a midpoint by trapping vacuum and atmospheric pressure, which keeps the diaphragm balanced.

Question 20

All of the following are types of vacuum boosters EXCEPT:

Accepted Answer

The other three options mentioned are all types of vacuum boosters.

Quiz 6: Power Brake Systems