car under chassis

8/3/2019 Car Under Chassis

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CAR UNDERCHASSIS

BRAKE SYSTEM SERVICING

Purpose of Brake System

1. Slow or stop the motion of the vehicle.2. Hold the vehicle while park on an inclined

General Classification

Service BrakesThese brakes are intended to reduce the speed of a car or bring to a standstill.

1. Hydraulic Brakes2. Air Brakes3. Electrical Brakes4. Mechanical Brakes


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Parking BrakesThis is intended to prevent the vehicle from rolling while parked or stop.

Retaders BrakesThis is a device which prevents the vehicle from over speeding downhill.


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HYDRAULIC BRAKE SYSTEM

A. FUNDAMENTALS OF BRAKE SYSTEM

Principle of Friction

Friction between the brake drum and brake lining slows the rotation of the wheels. Frictionbetween tires and the road surface slows the motion of the vehicle.

Friction varies according to the pressure applied between the sliding surfaces, theroughness of the surfaces, and the materials of which the surfaces are made.

1. Friction varies with the load applied between the sliding surfaces.2. Friction varies with the type of material.3. Friction at rest is greater than the friction of motion.

1 2 3

Principle of Hydraulic

The modern automobile uses hydraulic brake as a stopping medium. A special fluid(hydraulic fluid), confined in steel tubing lines, is used to transmit both motion and pressurefrom the brake pedal to the wheels.

1. Air is compressible. There is no pressure onpiston in A. In B, notice how pressure forcedpiston down.

2. Liquid cannot be compressed. Notice thatwhen the pressure is applied to piston in B, itdoes not compress the liquid.


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3. Liquid can transmit motion. Pressure is

applied in left cylinder forcing liquid to othercylinder causing movement of the cylinder

4. Liquid is used to transmit force.

5. Liquid is used to increase force

Pascals Principles

When pressure is exerted on a confined liquid, it is transmitted undiminished. Gaugesregister the same amount of pressure.


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Principles of hydraulic Jacks

This equipment shows how hydraulic fluid increases force.

B. MAJOR COMPONENTS OF H.B.S.

Master CylinderThis is used to pump out hydraulic brake fluid to the wheel brake assembly.

Pipes and hosesThis is used to transport fluid from the master cylinder to the wheel brake assembly.

Wheel brake assemblyThis is used to convert fluid pressure into mechanical force to produce brakes.

Pedal assemblyIt is a linkage that absorbs foot pressure and transmits it to the master cylinder piston.


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C. TYPES OF BRAKING ARRANGEMENT

This indicates how the master cylinder is connected to wheel brake assemblies. Thisdetermines also the type of master cylinder used in the system.

1. Single Braking SystemThis system uses a single mastercylinder to control both the frontand rear wheel brake assemblies.

2. Dual Split Front and RearThis system uses a double pistonmaster cylinder. The primarypiston controls the rear and the

secondary controls the front brakeassemblies.

3. Dual Split DiagonalThis system uses a double pistonmaster cylinder. The primarypiston controls the front right andrear left, while the secondarycontrols the front left and the rearright brake assemblies.


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D. OPERATION OF HYDRAULIC BRAKE SYSTEM

When the master cylinder operates it sends fluid via tubes to the wheel brake assembly, thewheel cylinder pistons and links push the brake shoes outward to contact with the drum. Asthe shoes cannot revolve, they will stop the drum and the wheel.

The kinetic energy in the moving car is converted into heat by the brakes

MASTER CYLINDER ASSEMBLY

A. COMPONENTS AND THE FUNCTIONS OF MASTER CYLINDER

Master Cylinder

It is used to pump brake fluid to the wheel brake assembly via tubes and hoses.

Components1. Reservoir

It is used to restore brake fluid. It has a cap that is vented to allow atmospheric pressureto act on the surface of the liquid to prevent vacuum.


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2. Cylinder bodyIt is provided with smooth inner wall. This contains piston assembly and has two ports,the compensating and the inlet ports. The compensating port which is ahead suppliesfluid to the pump out to the wheel brakes assembly. The inlet port allows fluid to lubricatethe piston and to prevent vacuum.

3. Piston assemblyIt is made of aluminum and is placed inside the cylinder body. It presses the primary cupwhich prevents internal leakage. The piston has small bleeder holes around the pistonhead. The secondary cup piston at the push rod side prevents fluid from leaving thecylinder.

4. Check valveIt is seated at the end of the cylinder body. It is a two-way valve design used to keep thestatic pressure inside the hydraulic system.

5. Return springIt is found inside the cylinder body and is used to push back the piston to its original

position after brakes has been applied.

6. Stop plate and snap ringIt prevents the piston assembly from coming out of the cylinder body.

7. Push rodIt applies pressure to the piston and is attached to the brake pedal linkage.

8. Rubber bootIt prevents external impurities to get inside the master cylinder body.

B. OPERATION OF MASTER CYLINDER

Released positionThe piston is position against the stop plate. Compensating port is open; static pressureis present inside the hydraulic brake system. Brake shoe return springs pull the shoefree of the brake drum.


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Application PositionThe brake pedal has forced the pushrod towards the master cylinder. Thisis forcing the piston deeper into themaster cylinder. Primary cup seals offcompensating port. Fluid flows through

inlet port to lubricate the piston.Pressure is created inside the cylinderand forces the check valve innerrubber to open and permit fluid to flowout of the master cylinder body to thefluid lines to the wheel brakeassembly.

Release - StartPedal force is removed. Push rodpressure is also removed, check valve

impedes the sudden return of fluid tothe master cylinder. Fluid flowsthrough bleeder ports at the pistonhead, as the fluid flows they bend thelips of the primary cup, and lips moveaway from the cylinder ahead of thepiston.

The flow of the fluid through thebleeder holes also prevent thepossible entry of air by keeping thecylinder filled at all times.

Pumping is the repeated application ofpedal force in quick movements.

Release - FinishPressure inside the master cylinderdrops as the pedal force is removed.The returning fluid forces the checkvalve rubber flap to close. The checkvalve is pushed off its seat, and fluidflows into the master cylinder. As thepiston against the stop plate, the

primary cup uncovers thecompensating port, and fluid returns tothe reservoir.

When the piston return spring pressureis again greater than the pressure ofthe returning fluid, the check valveseats, and will maintain the desiredstatic pressure inside the system.


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C. SERVICING OF MASTER CYLINDER

Disassembly

1. Remove the fluid reservoir tank.a. Loosen the stopper ring at the bottom of the reservoir tank.

2. Remove the snap ring.a. Remove the boot.b. Push piston No. 1 into the cylinder.c. Remove the snap ring with the piston pushed in

3. Remove the pistona. Remove the stop bolt with the piston pushed in.

i. Push piston No. 1 into the cylinder.b. Remove the pistons No. 1 and No. 2 and return springs No. 1 and No. 2.

i. Tap the cylinder tightly.4. Remove the check valve.

a. Remove the valve cap.b. Remove the check valve and valve spring.

5. Clean the removed parts.a. Clean the parts in brake fluid.

Inspection of Tandem Master Cylinder

1. Inspect the cylinder.a. Inspect for cracks or damage.

b. Inspect the inside face for spot wear, damage or rust.2. Inspect the piston assembly.

a. Inspect the piston for spot wear, damage or rust.b. Inspect the piston cup for wear or damage.c. Inspect the spring for damage, deformation or rust.

3. Inspect the boot.a. Inspect for damage or deformation.

4. Inspect the check valve.a. Inspect for damage or deformation.

b. Inspect the spring for damage, deformation or rust.

5. Cleaning of Parts.a. Clean all parts with brake fluid.

Safety: Do not use the petroleum base fluid like gasoline, diesel and kerosene.

b. After cleaning the parts, dry them with compress air


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6. Reassembly of Master Cylinder.a. Replace parts with new ones whenever specified to do so.b. Piston cups position always facing the fluid.c. Sequence of parts must be noted especially when working on a tandem master

cylinder.

7. Bench Bleeding.a. To ensure that the master cylinder compensates at both ports.b. This is to remove air present inside the master cylinder.c. While pumping the piston observe if bubbles appear.

8. Installation.a. Observe the proper torque of nuts.

9. Testing.a. Start engine and pump the brake pedal, adjust engine speed with accelerator.b. Observe the foot pressure if it is increasing.

WHEEL BRAKE ASSEMBLY

Drum Brake Assembly

It is an external expanding brakes that convert fluid pressure from the master cylinder to amechanical force to produce braking action. Its principal components are the brake drum,backing plate, brake shoes and tensioning devices.

Parts of a Drum Brake and their Functions

1. Brake drumIt is the rotating element of the assembly, bolted to the wheel hub between the hub andthe wheel. This completely surrounds the brake shoe assembly and comes very close tothe backing plate. The outer rim of the drum is cast to the steel center section. Thebraking area is smooth, round and parallel to the shoe surface.

2. Backing plateIt is round, steel disc bolted to the spindle steering knuckle at the front and bolted to theaxle housing at the rear. This serve as a foundation where the wheel cylinder assemblyand brake shoe assembly are fastened. It is rigid and cannot move in any direction.

3. Wheel cylinderIt is used to transmit the master cylinder pressure to the brake shoes, force them againstthe drum. It is made of cast iron housing and contain two aluminum pistons, two rubbercups, spring expander, two push rods and two rubber boots, drilled holes for brake linesconnection for the bleeder plug.


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4. Brake shoeThese are stamped steel that contain the lining either riveted or bonded to it. Theprimary shoe faces the front of the car. The secondary shoe faces the rear of the car.The ends of these shoes are fastened to an anchor.

5. Brake liningIt is made of asbestos with some special compounds added to it to increase the frictionalcoefficient of the material.

6. Return springsThese are used to pull the shoes away from the drum and restore the normal gap whichis present when the brake is released.

7. Brake shoe adjusterIt is used to maintain the clearance between the brake shoes and the lining and drum.Common shoe adjusters are the star wheel adjuster, cam adjuster and the ratchet type.

8. Shoe hold down mechanism

It holds the brake shoe assembly to the backing plate. It is also maintain the alignment ofthe shoe to the backing plate.

Operation of Drum Brake Assembly

When the master cylinder forces fluid into the wheel here cylinder, the two pistons move apart.Push rod pushes pistons to move outward, they force the shoes against the drum thus the liningcontacts the drum. Friction between the lining and the drum slows down the rotation of thedrum.


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Types of Brake Shoe ArrangementsBrake shoe arrangement refers to the method of attaching the brake shoes to the backingplate. Some arrangements uses servo action where in one shoe helps the other shoe to applythe other shoe, as well as a self-energizing using the frictional force to increase shoe to drumclearance.

Servo-self Energizing BrakesThe primary shoe starts to move with the drum, applies pressure to secondary shoe.

Double-anchor BrakesEach shoe is fastened to a separate anchor. Shoe to drum alignment is secured byrotating eccentric shaped and/or pins.


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Single-Anchor, Self-Centering Brake

Shoe ends, where they butt against anchor, are free to move up and down andautomatically align with the drum. Primary shoe is self-energizing, the secondary is not.

Double Anchor, Double Cylinder Brake

The free end of each shoe is actuated toward the direction of drum rotation, both areself-energizing

Servicing of Drum Brake

Disassembly

1. Remove the brake drum.a. If the drum is difficult to remove, perform the following operation first.

i. Turn the brake adjuster to contact the brake shoe.ii. Screw bolts into two threaded holes on the drum to raise the drum from its

mount.

2. Remove the front brake shoe.a. Remove the tension spring.b. Remove the shoe hold down spring and pinc. Remove the brake shoe.

i. Do not get oil or grease on the shoe.

3. Remove each tension spring.a. Remove the tension spring for anchor.b. Remove the tension spring and parking brake shoe strut from the rear brake

shoe.

4. Remove the rear brake shoe.a. Remove the shoe hold down spring and pin.b. Remove the tension spring for the automatic adjuster.c. Remove the support pin from the parking brake lever.d. Remove the parking brake cable from the parking brake shoe lever.e. Remove the following parts from the brake shoe.

i. C-washerii. Parking brake shoe leveriii. Automatic adjustment lever

Reassembly

1. Reassemble the brakea. Pay attention to the following points:

i. Ensure the proper position, direction and installing sequence of parts.ii. Do not get oil or grease on the brake shoe or on the inner surface of the

brake drum.


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On dry pavement, good drivers only apply enough pedal pressure to almost reach tire skid.They will release pedal pressure slightly when the squeal of tire skid is heard or felt. On slickpavement (water, snow, or ice on road surface), good drivers might pump the brake pedalmanually to reduce skidding and stopping distance.

This is the principle of anti-lock brakes. For maximum stopping power, you want the tires to

almost, but not quite, skid. When the tire skids, its friction with the road surface drops andstopping distance increases, which could cause an accident.The anti-lock brake system improves driver and passenger safety by reducing stoppingdistances and increasing directional stability under panic stop conditions.In this example, one side of the road is very slippery and the other side is dry. This poses aproblem if a panic stop is required.Without ABS, the car would tend to skid to the right because of higher tire adhesion on the right.With ABS, the car would still travel straight ahead with hard braking. The brake units would becycled to prevent tire skid and a loss of control. Also note that the car can be steered while

braking with ABS.

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