B - Hydraulic Brake System (Drum and Disc)

Question 1

Brake drums used on medium duty trucks are usually made from the following material.

Answer 1

Cast iron or centrefuse.

Question 2

List three functions of the drum brake backing plate.

Answer 2

Mounting points for: the anchor(s); the wheel cylinder(s).
Inspection holes for lining-to-drum clearance.
Service access holes for brake adjustment; brake bleeder screw(s).

Question 3

Brake shoe assemblies could be classified as servo acting or non-servo acting. What are the differences?

Answer 3

Servo action occurs when one shoe is positioned so it can move the other shoe during brake application. Non-servo action means both brake shoes act independently of each other.

Question 4

What is the purpose of brake shoe return springs?

Answer 4

Return brake shoes to released position. Prevents brake drag. Indirectly forces brake fluid back to the master cylinder.

Question 5

What are two functions of a disc brake caliper?

Answer 5

Provides cylinder bore(s) for caliper piston(s).

Holds inner and and outer disc brake pads.

Question 6

Disc brake pad lining material is generally described as:

Answer 6

Non-asbestos organic (NAO).

Semi-metallic.

Question 7

What is the purpose of vented disc brake rotors?

Answer 7

Vents provide increased cooling air flow during vehicle operation. This helps to dissipate rotor heat faster.

Question 8

True or False: Disc brakes have both servo and self-energizing action.

Answer 8

False, Disc brakes have neither. They rely on a clamping force.

Question 9

Why do master cylinders generally have two separate reservoirs?

Answer 9

Safety is the prime reason. Two independent systems exist. Failure in one system does not affect the other system.

Question 10

The master cylinder has two small ports leading into the cylinder bore from each reservoir. What is the name and purpose of the smallest port?

Answer 10

Compensating port. Allows brake fluid into the cylinder bore as the brakes are being released. Allows heated brake fluid to expand into the reservoir to prevent brake drag. Allows cooled fluid to return to the cylinder bore.

Question 11

True or False: A horizontally mounted master cylinder has a primary and a secondary piston. The primary piston is the first one activated by the brake pedal pushrod.

Answer 11

True.

Question 12

How is the secondary piston in the master cylinder moved during normal braking operation?

Answer 12

The primary piston moves; the compensating port is closed; brake fluid is trapped between the primary and secondary piston.

Question 13

True or False: Double flares and ISO flares are the two types of flares used on steel brake tubing.

Answer 13

True.

Question 14

True or False: Steel tubing with double flares can be used with fittings that are designed for ISO flares.

Answer 14

False, Double flares and fittings must never be interchanged with ISO flares and fittings.

Question 15

Why are flexible hoses used as brake lines?

Answer 15

To prevent line breakage as components move.

Question 16

To protect brake line fittings from damage the following tools should be used:

Answer 16

Line/Flare nut wrenches.

Question 17

True or False: Pressurized brake fluid moves the piston seal and the piston in a drum brake wheel cylinder.

Answer 17

True.

Question 18

True or False: Pressurized brake fluid moves the piston seal and the piston in a disc brake caliper.

Answer 18

False, Fluid moves piston only.

Question 19

True or False: Wheel cylinders are mounted on backing plates. Calipers are mounted on anchor plates.

Answer 19

True.

Question 20

What is the purpose of the outermost seals or boots used on wheel cylinders and caliper pistons.

Answer 20

Prevents dirt, water or lining dust from damaging or contaminating the pistons, the cylinder bores or the brake fluid.

Question 21

True or False: After brake pedal release, caliper pistons return by piston seal movement. Wheel cylinder pistons return due to the action of the brake shoe return springs.

Answer 21

True

Question 22

Brake systems may include a residual check valve. What is the function of this type of valve?

Answer 22

Maintains a very small amount of line pressure. This helps prevent air seepage past piston seals, yet does not allow brake drag.

Question 23

What is the function of a metering valve?

Answer 23

Used in disc/drum brake system. Prevents disc brakes from applying until line pressure in drum brake system overcomes brake shoe return spring tension.

Question 24

What is the function of a proportioning valve?

Answer 24

Helps prevent rear wheel lock-up by restricting fluid pressure build-up to the rear brakes, under heavy braking application.

Question 25

What is the function of a pressure differential valve?

Answer 25

Activates brake warning or brake failure light on the dash when fluid pressure is lost in one brake system. Can be used to indicate emergency brake application.