B - Hydraulic Brake System (Drum and Disc) Flashcards

1
Q

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

A

Cast iron or centrefuse.

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2
Q

List three functions of the drum brake backing plate.

A

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).

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3
Q

Brake shoe assemblies could be classed as servo acting or non-servo acting. Explain the differences.

A

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

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4
Q

Explain the purpose of brake shoe return springs.

A

Returns brake shoes to release position. Prevents brake drag. Indirectly forces brake fluid back to the master cylinder.

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5
Q

List two functions of a disc brake calliper.

A

Provides cylinder bore(s) for calliper piston(s) and holds inner and outside disc brake pads.

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6
Q

Disc brake pad lining material is generally described as:

A

Non-asbestos organic (NAO) and semi-metallic.

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7
Q

Explain the main purpose of vented disc brake rotors.

A

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

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8
Q

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

A

False; Discs brakes have neither. They rely on a clamping force.

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9
Q

Explain why master cylinders generally have two separate reservoirs.

A

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

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10
Q

The master cylinder has two small ports leading into the cylinder bore from each reservoir. Name and explain the purpose(s) of the small port.

A

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.

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11
Q

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

A

True.

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12
Q

Explain how the secondary piston in the master cylinder is moved during normal braking operation.

A

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

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13
Q

True or False: Double flares and ISO flares used on steel brake tubing.

A

True.

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14
Q

Steel tubing with double flares can be used with fittings that are designed for ISO flares.

A

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

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15
Q

Explain why flexible hoses are used as brake lines.

A

To prevent line breakage as components move.

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16
Q

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

A

Line/Flare nut wrenches.

17
Q

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

A

True.

18
Q

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

A

False; Fluid moves piston only.

19
Q

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

A

True.

20
Q

Explain the purpose of the outermost seals or boots used on wheel cylinders and calliper pistons.

A

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

21
Q

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

A

True.

22
Q

Brake systems may include a residual check valve. Explain the function of this type of valve.

A

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

23
Q

Explain the function of a metering valve.

A

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

24
Q

Explain the function of a proportioning valve.

A

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

25
Q

Explain the function of a pressure differential valve.

A

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