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Brakes > Hydralic Brakes > Flashcards

Hydralic Brakes Flashcards

1
Q

What characteristics dose brake fluid have to do?

A 
Low viscosity 
Compatibility with rubber components 
Must not chemically react with the rubber seals and metals 
High boiling point 
Low freezing point 
Fluid compatibility 
Resistance to chemical ageing
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2
Q

Main disadvantage fo brake fluid?

A

It’s hygroscopic. This means that is absorbs moisture from the air

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3
Q

What enables free play to be set between push rod and master cylinder?

A

Adjustable push rod

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4
Q

Why is free play important?

A

Without free play the brakes may not release fully

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5
Q

Why is a check valve fitted to a basic single piston barrel type master cylinder?

A

To allow florid in both directions depending on wether the brakes are applied or released

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6
Q

What is the biggest disadvantage of a single piston barrel type master cylinder?

And how do you prevent this?

A

If there was a break in the brake pipe, braking ability will be lost

To prevent this the braking system was designed know as a divided line braking circuit

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7
Q

What are the 3 commonly used divides?

A

Front/rear split
X split
L split

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8
Q

How dose the pressure differential warning indicator work?

A

When the pressure between the two lines of a split systems is unequal

Pressure drops on line A, allowing side B to push piston across. Raising the ball to activate the sensor

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9
Q

What are the characteristics of brake pipes?

A

Narrow bore
Usually made of steel
Seamless to cope with operational pressures

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10
Q

2 common types of wheel cylinders?

A

A double acting type

A single acting type

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11
Q

Say information about a double acting type?

A

Bolted to the backplate
Used on a leading/trailing show set up
Only one required
Contains 2 pistons that move outwards when pressurised
Hydraulic fluid comes in and pushed the pistons out

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12
Q

Say information about a single acting cylinder?

A

Bolted to backplate
Used in a twin leading shoe set up
Contains single piston that is pushed out by hydraulic pressure

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13
Q

What is the purpose of the show adjusters?

And why is it needed

A

To ensure that shoes sit as close to drum without binding so that minimum pedal movement is required to apply brakes

When friction lining wears due to use
When sitting up brakes after they have been worked

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14
Q

What are the 3 designs of shoe adjusters?

A

Snail cam
Wedge and tappets
Screwed plug type

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15
Q

What are the 2 main variants of automatic adjusters?

A

One that works off the foot brake

One that works off the handbrake

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16
Q

Why are brake pad and discs for favourable for heat reduction?

A

Hot spot it localised

Larger area is exposed to the atmosphere - improving heat dissipation

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17
Q

What are the 2 types of brake pad and discs?

A

Solid or vented type

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18
Q

How does the vented type brake disc dissipate heat?

A

Directs air through the centre of the disc

Increases the surface area exposed to the atmosphere

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19
Q

What does the groove in the brake pad allow?

A

Dust to escape

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20
Q

What do some pads incorporate?

A

Wear indicator that illuminates a light in the cab

21
Q

Where are the pads housed?

A

Brake callipers

22
Q

What does the seal between the piston and cylinder do?

A

Prevents brake fluid leaking passed the piston

23
Q

What does the dust shield do?

A

Prevents an ingress of dirt and water

Which could damage or corrode the pistons or cylinder

24
Q

What is the area behind the piston known as?

A

Fluid chamber

25
Q

How are the 2 chambers connected?

A

Internal drilling

26
Q

What is the operation of the disc brake with hydraulic cylinders?

A

Brake pedal is depressed , pressurised fluid acts on the pistons

Equal pressure is felt on both sides of the piston

Brake pads move inwards clamping the disc

27
Q

What retracts the pistons so that the brakes are released?

A

The seal between the piston and cylinder

28
Q

How does the seal retract the cylinder?

A

The seal is distorted

When brakes are released the seal returns to its original shape pulling the piston away from the disc

29
Q

What are the 3 functions of the seal?

A

Prevents leaking of the brake fluid

It retracts the piston on release of the brake

When the brake pad lining wears the it is self adjusting meaning it will adapt when the pad wears

30
Q

What are the advantages of disc brakes?

A

Braking surface is directly exposed to the air, easier heat dissipation

Give braking torque proportional to the applied force

Weight saving

31
Q

What is the method used to boost driving effort on hydraulic brakes?

A

Brake servo

32
Q

What is the servo connected to?

A

Inlet manifold and vacuum pump

33
Q

What is the chamber of the servo divided into?

A

Front and rear chamber

34
Q

The larger the diaphragm the greater the….

A

Assistance

35
Q

What returns the servo to the off position?

A

Spring

36
Q

What is the atmospheric valve moved by?

A

Brake pedal push rod

37
Q

What is the vacuum valve moved by?

A

Spring

38
Q

What position is the valves when the brakes are off?

A

Atmospheric closed and vacuum open

39
Q

On a petrol engine the connecting hose is attached to what?

A

Inlet manifold

40
Q

On a Diesel engine the connecting hose is attached to what?

A

Vacuum pump

41
Q

What happens when the brakes are applied?

A

Push rod moves the atmospheric valve piston forward

Vacuum piston also moves forward which closes off the vacuum passage

The front and rear chambers are no longer connected

Further movement of brake , lifts atmospheric valve off its seat allowing air at atmospheric pressure to be delivered to the rear chamber

As the air in the rear chamber is greater than the front , the diaphragm is pushed forward giving desired boost

42
Q

What happens if the servo fails?

A

Greater effort required by the driver

43
Q

What happens when brakes are held on?

A

Both valves are closed and pressure is exerted on the master cylinder by the aid of the reaction disc . Back pressure closes off the air valve

44
Q

What type of shoe set up is used with a single acting cylinder?

A

Twin leading shoe set up

45
Q

Alternative name for snail cam?

A

Striker pin

46
Q

Where is the screwed plug type adjuster located?

A

It’s incorporated into the wheel cylinder

47
Q

What connects both shoes on a automatic adjuster, foot brake operated?

A

A cross strut

48
Q

Why dose the ratchet on a automatic adjuster (foot brake operated) have a hole in it?

A

To accommodate a lug on the cross strut

Brakes (3 decks)

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