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Larry’s New truck

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Larry’s Truck Improvements

• Larry put a 6” lift kit on his Ford F-150 and a set of 33’s Super Swamper Thornbird Tires

• The Suspension System has been modified but the Brake System has not.

• Do You See Any Problems?

GIT-R-DONE

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What Parts Control the Stopping of the Truck?

• Master Cylinder

• Brake Hoses/Lines

• Wheel Cylinders

• Brake Calipers

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Larry has a Problem!

• What changes could you make to fix the problem?– Bigger parts

• Such as: Master Cylinder, Brake lines, Wheel Cylinders, and/or Brake Calipers

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Pascal’s Law

Unlock the mechanics of the Hydraulic Braking System

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Before we apply Pascal’s Law

We must first review and be familiar with… Diameter of a Piston Radius of the Piston Area of the top surface of the Piston

Mathematically speaking…

Diameter: The width of a circular or cylindrical object.

Radius: The radius of a circle is half the diameter Area: Any particular extent of space or surface

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Math – Hands on Practice Measure across the top

of the piston, through the center and record the diameter (inches)

Calculate the radius of the piston

Calculate the area of the top of the piston

A = π · r · r orA = πr2

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Area Example

Diameter = 7 inches Radius = 3 1/2 inches Area = ?

A= π·r2

3.14 · (3 ½ in)2 = 38.465 in2

Area = 38.465 in2

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Homework

Practice skill work Read article: Effect of Oversize Tires

on Braking Characteristics – www.aamva.org/Documents/

vehStudyEffectOfOversizedTiresOnAlteredHeightVehicles.pdf -

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Pascal’s Law In the 1600's, the French scientist Blaise

Pascal discovered a fact now known as Pascal's Law. It states that pressure at any point in a body of fluid is the same in every direction, exerting equal force on equal areas. This works for gases and liquids (both are fluids).

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Pascal’s Formula

This brings us to a very important formula:

P = Pressure, F = Force and A = Area

This expresses that Pressure is Force per Unit Area. This is why pressure is usually expressed in pounds per square inch (psi).

A

FP

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Variations of Pascal’s Law

Pressure = Force divided by area

Force = Pressure times area

Area = Force divided by pressure

A

FP

APF

P

FA

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F

P A

F =Force

P = Pressure A = Area

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Have you used formulas like Pascal’s Law? Where are they used?

Generic Inverse Variation Problem

used in Algebra Time = Distance / Rate

Ohm’s Law

used in science class with electrical components

xy

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Using Pascal’s Law

Pascal's Law - gives us the mechanics to do a great deal of work with hydraulics. The drawing on the left shows that we can lift a large amount of weight with a small amount of effort. We can lift 100 pounds by applying just 10 pounds of force to the piston measuring 1 square inch

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Basic automotive braking system

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50 lbs force.5 sq in area of top of piston

50 lbs divided by .5 = 100 psi

A

FP

25.

50

in

lbP

2/100 inlbP

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Where might Pascal’s Law be used?

A twenty ton floor jack has a hydraulic piston with a 7 in diameter.

60 pounds of force is being applied to the piston.

Calculate the line pressure being exerted on the piston.

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Solving a Pascal’s Law problem Which version of Pascal’s Law will you use?

Pressure = Force divided by area

Recall from earlier…..

A= π·r2

3.14 · (3 ½ in)2 = 38.465 in2

Area = 38.465 in2

P = (60pounds) / (38.465 in2)

P = 1.56 pounds/ in2

P = 1.56 psi

A

FP

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Using Pascal’s Law

A caliper piston has a diameter = 1.5 in

The Master cylinder has 50 pounds per square inch (psi) line pressure applied to it.

Determine the force exerted on the caliper piston.

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Solving a Pascal’s Law problem Which version of Pascal’s Law will you use? Force = Pressure times area

Recall how to find area….. A= π·r2

3.14 · (3/4 in)2 = 1.77 in2

Area = 1.77 in2

F = (50pounds/ in2) (1.77 in2)F = 88.5 pounds

APF

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Did Larry have brake failure?

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Remember Larry’s Truck ……..

The truck has a major braking problem.

You suggested earlier that we replace it with bigger brake parts…

What do we need to know about the original braking system?

GIT-R-DONE

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Facts about Larry’s Truck

¼ in brake lines ½ in bore master cylinder 7/8 in bore wheel cylinders 2 in caliper pistons

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Can you fix Larry’s truck?

Devise a plan to fix Larry’s truck based on Pascal’s Law and your knowledge of automotive systems that will remedy Larry’s braking problems.– Be sure to show all calculations and justify

your solution plan in a written paragraph.

Remember Larry doubled the size of the original tire size…..

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Be thorough..Larry is depending on you…

How would you

–“Git-R-Done”?

GIT-R-DONE