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Heavy Equipment Technician Hydraulic System (Drum & Disc)

Hydraulic Brake Systems First Period Module 190103b Objectives 1. Explain the principles of operation of a system

2. Explain the principles of operation of a disk brake system

3. Explain the operation and construction of master cylinders Objectives 4. Explain the purpose and construction of brake lines and hoses

5. Explain the operation and construction of cylinders and calipers

6. Explain the purpose and operation of the metering, proportioning and differential valves Objective One Explain the principles of operation of a drum brake system Drum Brake System Components

Wheel Assembly Backing Plate The backing plate serves as a rigid mounting surface as well a a dust and rock shield.. Backing Plate

It is bolted solid to the housing and includes a number of holes. The lining is riveted, bolted or glued in place

Two brake shoes are used Lining T - Shape at each wheel, they are made from stamped steel and welded in a T shape.. Brake Shoe Actions Self – Energizing Action

Moving Forward Moving Backward

F – Forward Shoe R - Reverse Shoe Greater output force with lower input force occurs, when the shoe tends to wrap itself into the rotating drum. Servo Action

Moving Forward Moving Forward

Secondary Shoe

Primary Shoe Slack Adjuster Happens when the primary shoe self energizes and helps to apply the secondary shoe through the slack adjuster, then the secondary shoe will also self energize. Non – Servo Action Non servo brake shoe operate independently.. There is no connection Moving Forward between the shoes.. Forward acting shoe: Self energizes in forward only..

Reverse acting shoe: Self energizes in reverse only. Forward Reverse Acting Shoe Acting Shoe Non – Servo Action Non servo brake assembly using two, two wheel cylinders.. Moving Forward Both shoes will self- energize in both directions, but are still called forward and reverse acting shoes

Forward Reverse Acting Shoe Acting Shoe Non – Servo Action Two leading shoe design, assembly using two single piston cylinders.. Moving Forward Both shoes self- energize in a forward direction, but will not self-energize in reverse.

Forward Reverse Acting Shoe Acting Shoe Brake Shoe Lining Non - Asbestos Organic Linings A high stable co-efficient of friction, low wear rate, high resistance to heat and low noise.. Most common, and may include small amounts of fiberglass, armid fibers, ceramics or carbon. Brake Shoe Lining Semi – Metallic Linings For high heat applications and are less susceptible to .. Similar to organic linings, but contain chopped, powdered or sintered metal particles such as iron or steel for high demand, and copper or brass for low demand application. Wheel Cylinders Made of cast iron, 1 or 2 to a wheel and operates the brake shoes.

Brake Hardware Consists of springs, pins, and clips to control brake shoe movement and locate onto the backing plate.. Springs may be color coded for proper position. Brake Drums May be of a centrefuse construction of a steel outer shell with a cast iron liner.. Hub

Drum

Most large drums are single piece cast iron. Objective Two Explain the principles of operation of a disk brake system. Systems Caliper Advantages: Better straight line stops.. Self adjusting.. Self centering.. Caliper Less water fade.. Less brake fade.. Less moving parts.. Economy of operation.. Ease of inspection and maintenance. Brake Caliper

Caliper Housing Bleed Screw

Boot, Dust

Shield Piston Seal

May be of the single or double piston design and receives fluid pressure through lines and hoses from the . Brake Caliper

Brakes Applied Released

Square Seal Square Seal

The piston is returned to the rest position by the square seal.. With pressure applied the rotor is “pinched” between the brake pads. Brake Caliper Floating Caliper Fixed Caliper Dust Boot Rotor

Pads

4 Can be a floating caliper or fixed caliper design. Brake Disc or Brake Rotor Rotors or disks are made of cast iron, absorb considerable heat energy, and may be vented for cooling. Brake Pads Pads are made of the same materials as shoes..

Linings are glued or New Pad Worn Pad riveted on a steel back..

May contain a wear Rotor indicator or an imbedded sensor in Lining the lining with a light in the dash.. May have anti squeal springs or material on Lining Wear the steel back. Indicator Objective Three Explain the operation and construction of master cylinders Master Cylinder RESERVOIR COVER DIAPHRAM RESERVOIR DRUM BRAKE Seals out dirt & DISC BRAKE SYSTEM moisture SYSTEM

PUSH ROD B A DRUM BRAKE OUTLET DISC BRAKE A B OUTLET PRIMARY PISTON SECONDARY PISTON Forces fluid to disc Forces fluid to drum brakes. brakes. Master Cylinder COMPENSATION PORT FLUID INLET PORT Allows fluid to flow between Maintains fluid under the reservoir and pressure atmospheric pressure to chamber. the centre area.

B A

CUP SEALS PISTON CUP SEALS Isolate primary & Prevents fluid from secondary systems. leaking past piston. Components Master Cylinder Compensating Primary Piston Secondary O-Ring Poppet O-Ring Return Spring Piston Seal Stop Pin Seal Back-up Primary Piston Function: Develops necessary pressure.. Supply fluid for cylinders and pistons.. A fluid reservoir which allows fluid to expand and contract. Master Cylinder

May be one piece cast Master Cylinder iron or two piece, Clevis plastic reservoir and aluminum cylinder..

Lever arrangement will Bulkhead increase mechanical Push Rod advantage to increase force to the push rod. Brake Pedal Master Cylinder Reservoirs maybe the same size or different sizes (disc brakes require more fluid).. Drum Brake Disc Brake Reservoir Reservoir

B A

Both reservoirs are separate from each other for safety reasons. Master Cylinder Pistons Secondary Piston Cup Secondary Piston Seal Compensating Fluid Level Port A Released Secondary Position Primary Piston Cup Piston Cup

A. Primary Piston Is the rear piston which supplies fluid to the disc brakes, and contains a primary and a secondary seal. Master Cylinder Pistons Secondary Piston Cup Secondary Piston Seal Compensating Fluid Level Port A Released Secondary Position Primary Piston Cup Piston Cup

A. Primary Piston Primary Piston Cup Seal sits between the compensating port and the inlet port. (at rest) Master Cylinder Pistons Secondary Piston Cup Secondary Piston Seal Compensating Fluid Level Port

B Released Secondary Position Primary Piston Cup Piston Cup

B. Secondary Piston Is the front piston and supplies fluid to the drum brakes, and contains a primary and secondary seal. Master Cylinder Pistons Secondary Piston Cup Secondary Piston Seal Compensating Fluid Level Port

B Released Secondary Position Primary Piston Cup Piston Cup

B. Secondary Piston Secondary Piston Seals prevents fluid from transferring from the primary section to the secondary section. Master Cylinder Pistons Secondary Piston Cup Secondary Piston Seal Compensating Fluid Level Port

B Released Secondary Position Primary Piston Cup Piston Cup

B Secondary Piston Primary seal sits between the compensating port and the inlet port. (at rest) Master Cylinder Pistons

Bulkhead Pedal Depressed Height. (Brakes Applied)

Pedal Free Height.

Pedal Reserve Pedal Travel to Apply Brakes 20% or More. 80% or Less of Total. As pedal is released, the piston return springs and pressurized fluid ensure the primary and secondary piston quickly return to at rest. Master Cylinder Ports

Inlet Port Inlet Port

Primary Returning Piston Cup Piston Inlet port keeps master cylinder full at all times. During a fast brake release or when the brakes are being pumped, the piston returns faster than the fluid from the brakes.. This ensures that the system remains full. Master Cylinder Ports

Compensating Port

B A

Compensating Port Allows fluid return after a brake application.. Will compensate for temperature change. (Fluid Expansion) Master Cylinder Action during System Failure If the primary system develops a leak, the primary piston butts up against, and AA B B mechanically applies the secondary piston..

Rear drum breaking is available. Master Cylinder Action during System Failure If the secondary system develops a leak, the primary piston hydraulically AA BB moves the secondary piston to the bottom of the master cylinder..

Front disc breaking is available. Low Level Warning System Brake Fluid Level Switch Reservoir

Brake Fluid Level Switch Uses a magnetic float assembly to activate the electrical switch. Objective Four Explain the purpose and construction of brake lines and hoses. Brake Lines and Hoses Steel Brake Lines Made from double wall steel tubing.. Must meet a specific standard.. Contains a double flair.. May have a spring coiled around it, for protection.. Must only use proper bending equipment and proper steel line Must be secured along its length to prevent vibration. (metal fatigue) Brake Lines Flares Double Flares Hydraulic brake lines are usually double flared.

ISO Flares Steel tubing are also constructed with International Standards Organization flares. ISO Flares An ISO flare is constructed using a special flaring tool.. Invert forcing screw.. Bottom it in block.. Push tubing Up into Block.. Correct Amount of Tubing Left in Block. ISO Flares Clamp in Vice at Line.. Turn Forcing Screw Until it Bottoms. Flexible Brake Hoses Brake hoses are flexible, withstand high pressure without stretching or bulging under load..

Have a high pressure neoprene centre hose with a rayon braid cover for protection. Flexible Brake Hoses

Fittings are permanently attached.. Used where movement between two components will occur. Hydraulic Brake Fitting Using flare nut wrenches of the correct size will result in less damage and proper sealing of the fitting. Objective Five Explain the operation and construction of wheel cylinders and calipers Wheel Cylinders Wheel cylinders convert hydraulic pressure into force to push out the Wheel Cylinders brake shoes..

Mounted to the backing plate, and located between the brake shoes..

Two wheel cylinders will be interconnected with a brake line. Single Piston Wheel Cylinders Made of cast iron with an aluminum piston..

A rubber seal is used Boot Seal Spring to prevent leakage..

The boot prevents the entry of dirt and water.. Piston A push rod is used to connect the piston to the brake shoe. Two Piston Wheel Cylinders The cup type seals may incorporate an expander and spring to keep the outer lip of the seal against the cylinder bore to prevent the entry of air.. A bleeder screw is used to allow the removal of air in the brake fluid. Two Piston Step Bore Wheel Cylinders A stepped bore may be used when greater force is required to one side only..

Used in specific applications and should not be replaced with a straight bore wheel cylinder. Adjuster Style Wheel Cylinder Some wheel cylinders only activate during braking..

Brake adjustment is done with another mechanism. Disk Brake Calipers Outer Pad Caliper

Piston

Steering Knuckle Made of cast iron with a steel or phenolic (plastic) pistons.. Pinches the disc between two pads. Disk Brake Calipers Convert hydraulic pressure into force..

Boot Seal

Brake Piston Fluid

Bore

Can have one or more pistons depending on the force required. Disk Brake Calipers Caliper pistons have no return springs.. Applied Piston Released Retraction

Seal Flex

Piston seal flex will retract the piston and also maintain clearance between pad and disc. Floating Calipers One, two or more pistons are in one side of the caliper.. Caliper Pads

Piston

Rotor Piston Seal Dust Boot The force of the piston pushing the pad onto the disc will cause the caliper to slide, and bring the other pad into contact with the disc. Floating Calipers Sliding calipers mount directly on the steering knuckle and slides Pin Caliper Way or floats on the Bushing guide pins.. Caliper

Caliper Support Floating calipers Guide Ways work the same as sliding calipers except guide pins are used to mount the caliper to the steering knuckle Floating Calipers Floating Caliper are mounted to the anchor plate using a key and spring.

Spring Allen Head Caliper Bolt Key Wear Shim Anchor Plate Cleanliness and freedom of movement between components ensures proper braking. Fixed Calipers Pistons on either side of the disc push the pads into contact with the rotor..

Caliper Pads Piston Seal

Rotor

Pistons

Fixed calipers are mounted solid to the steering knuckle. Objective Six Explain the purpose and operation of the metering, proportioning and differential valves Differential Valves Residual Check Valve A small valve that is placed on the outlet of the master cylinder to the drum brakes only.. Used on maintains a small amount of pressure (12 - 15 psi) in the line and wheel cylinder to keep the piston cup seals against the cylinder bore..

Prevents the entry of air into the system Differential Valves Residual Check Valve

Some systems do not use residual check valves but use expander cup and spring assemblies. Differential Valves Brake Failure Warning Valve

Pressure Differential Indicator Assy. Located close to or on the master cylinder, and pressure loss illuminates a brake warning light . Differential Valves Brake Failure Warning Valve The piston senses pressure from both sides of the master cylinder.. When there is a sudden fluid loss from the front or rear section of the master cylinder, the piston is pushed across and activates the switch and illuminates a brake failure warning light on the dash. Differential Valves From Master Metering Valve Cylinder

Is used on front To To L F brakes only.. R F Brake Brake Restricts pressure Valve build up in the disc Plunger brakes system until the drum brakes activate.. Valve opens about 130-135 psi.. Allows the drum brakes and disc brakes to activate together. Differential Valves

Metering Valve RF

Valve Stem Push-In or LF Pull-Out. Valve Button Push–In Only

With special tools the valve button and valve stem may need to be physically opened, for the process. Differential Valves Metering Valve Compensates for sudden weight transfer to the front.. From Master Cylinder To Rear Brake

Prevent rear wheel lock up during heavy brake application. Differential Valves Metering Valve Bracket Weight or height Lever sensing proportioning Assy. valves may be used on vehicles that carry cargo.. Proportioning Valve Excess weight in the Push Rod Clamp back requires more pressure to the rear Set Screw brakes. Lower Bracket (on axle housing) Differential Valves Combination Valve Metering Valve Brake Failure Proportioning Valve Warning Valve From Master Cylinder To LF Outlet to Brake Rear Brakes

Valve Stem O-Rings To RF Brakes Pressure Differential Piston Front Brakes Rear Brakes THE END