190103 D Flashcards
Brake drums used on medium duty trucks are usually made from which material?
cast iron or centrefuse
List three (3) functions of the drum brake backing plate.
- 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)
Brake shoe assemblies could be classed as servo acting or non-servo acting. Explain the differences.
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.
Explain the purpose of brake shoe return springs.
Returns brake shoes to released position. Prevents brake drag. Indirectly forces brake fluid back to the master cylinder.
List two functions of a disc brake caliper
- Provides cylinder bore(s) for caliper piston(s).
- Holds inner and outer disc brake pads.
Disc brake pad lining material is generally described as:
non-asbestos organic (NAO)
Explain the main purpose of vented disc brake rotors
semi-metallic vents provide increased cooling air flow during vehicle operation. This helps to dissipate rotor heat faster.
Do disc brakes have both servo and self-energizing action?
No, discs brakes have neither. They rely on a clamping force.
Explain why master cylinders generally have two separate reservoirs.
Safety is the prime reason. Two independent systems exist. Failure in one system does not affect the other system.
The master cylinder has two small ports leading into the cylinder bore from each reservoir. Name, and explain the purpose(s) of the smallest port.
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.
A horizontally mounted master cylinder has a primary and a secondary piston. Which is the primary piston?
The primary piston is the first one activated by the brake pedal pushrod.
Explain how the secondary piston in the master cylinder is moved during normal braking operation
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.
________ flares and _______flares are the two types of flares used on steel brake tubing.
Double and ISO
Double flares and fittings must never be interchanged with _______flares and fittings.
ISO
Explain why flexible hoses are used as brake lines.
To prevent line breakage as components move.
To protect brake line fittings from damage which tools should be used?
Line/Flare nut wrenches.
What moves the piston seal and the piston in a drum brake wheel cylinder?
Pressurized brake fluid
Wheel cylinders are mounted on backing plates. Calipers are mounted on _______________.
anchor plates.
Explain the purpose of the outermost seals or boots used on wheel cylinders and
caliper pistons.
Prevents dirt, water or lining dust from damaging or contaminating the pistons, the cylinder bores or the brake fluid.
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.
Brake systems may include a residual check valve. Explain the function of this type of valve.
Maintains a very small amount of line pressure. This helps prevent air seepage past piston seals, yet does not allow braking.
Explain the function of a metering valve
used in disc/drum brake system. Prevents disc brakes from applying until line pressure in the drum brake system overcomes brake Shoe return Spring tension
Explain the function of a proportioning valve.
Helps prevent rear wheel lock-up by restricting Fluid pressure build-up to the rear brakes, under heavy braking application
Explain the function of a pressure differential valve.
Activates brake warning or brake failure light on the dash when
fluid pressure is lost
in the System.
