Heavy Equipment Technician Parking Brake System Fundamentals and Service

Hydraulic Brake Systems First Period Module 190103e Objectives

1. Explain the principles of operation for common parking brake systems..

2. Describe the adjusting procedures for common parking brake systems..

3. Describe repair procedures for common parking brake systems. Objective One

Explain the principles of operation for common parking brake systems.. Parking Brake Its designed is to hold the vehicle stationary.. It may be a sub-system of the service brakes.. It is NOT an emergency brake, but it may help to slow a vehicle down.. Caution Always fully apply a parking brake.. Partial application could allow a vehicle to roll away.. Driving with parking brake partially applied could cause a fire in the assembly. Wheel Types

Two Types:

1. Mechanical Linkage Type.. 2. Hydraulic Operated. 1. Mechanical Linkage Type Spring loaded foot pedal or hand lever pulls on a cable that is connected to the park brake assembly.

Release Handle

Cable Lever to Equalizer 1. Mechanical Linkage Type

Rear Park Brake Cables

Equalizer

Adjustment Screw & Nut The cable leads through an Equalizer, and the adjusting screw and nut of the park brake cable adjusts cable tension. 1. Mechanical Linkage Type Cable pulls on the brake lever attached to the secondary shoe and moves the strut, which transfers force to the primary shoe.. Secondary Shoe Front Strut Shoe Hold Primary Shoe Down Clip

Brake Lever Parking Brake Cable Brakes are released by the service brake springs. 2. Hydraulically Operated May use pressurized fluid from the power steering pump or the power brake booster to activate the park brakes..

Caution The fluid used in the park brake system is NOT brake fluid.. The park brake system is a separate hydraulic sub-system, which uses hydraulic fluid. 2. Hydraulically Operated Parking Brake Control Parking Brake Drum Brake Valve Unitized Valve Wheel Cylinders Parking Brake Reservoir & Pump

Disc Brake Hydro-Max Booster

Spring-Set Primary Hydraulic System Parking Brake Secondary Hydraulic System Parking Brake System 2. Hydraulically Operated. A Spring Set Parking Brake Chamber is used to apply the parking Wheel Cylinder Cylinder brake through the Assembly Bridge Line wedge of the Wheel & Park Cylinder Assembly..

Hydraulic pressure Backing is used to cage the Plate spring and release the parking brake. Wheel & Park Brake Shoe Cylinder & Lining Assembly 2. Hydraulically Operated Dust Boot Expander Piston To Power Spring Spring & Locator Chamber

Piston Seals Sleeve Hand Brake Piston Return Spring O-Ring Snap Ring Housing Wedge Assembly

Abutment Piston Park Brake Cylinder & Wedge Assembly 2. Hydraulically Operated Applied Condition Power To HR-1 Park Cylinder Assembly Relay Valve Spring Return Hand Spring Brake Piston

Power Wedge Spring & Roller Caging & Screw Assembly Diaphragm Oil is exhausted from the bottom of the diaphragm, and power spring pushes on the wedge and applies the hand brake piston. 2. Hydraulically Operated Released Condition Power From HR-1 Park Cylinder Assembly Relay Valve Spring Return Hand Spring Brake Piston

Power Wedge Spring & Roller Caging & Screw Assembly Diaphragm Hydraulic fluid pressure is delivered to the bottom of the diaphragm and compresses the power spring, return spring retracts the wedge. Driveshaft Type Mechanically Activated Internal Shoe Type Backing plate, hardware and shoes similar to a service drum brake are mounted to the rear of the transmission.. Transmission Housing Flexible Cable To Drive Shaft Parking Brake Control Drum The drum is attached to the driveshaft in some manner.. Driveshaft Type Mechanically Activated External Band Type Brake drum has an Parking Brake Control external friction surface.. Flexible Cable Brake Drum A metal brake band with a friction lining Transmission on the interior, Housing contracts around the brake drum and To prevents it from Drive Shaft moving. Driveshaft Type Disc Type May use one or two rotors (discs) attached to the transmission output shaft.. The pad assemblies are mounted to the transmission housing, and are activated by a lever and cable arrangement. Driveshaft Type Electric / Hydraulic Activated Parking Brake Cable Transmission Housing

Parking Brake Actuator To Drive Shaft

Electric Park Brake Pump Assembly Uses an electric parking brake pump assembly and a hydraulic / spring actuator to operate the brake shoes.. (similar to mechanical driveshaft brake) Driveshaft Type Electric / Hydraulic Activated Brakes are applied by Electric Pump Motor Power Connection spring pressure and released by hydraulic pressure..

The actuator is a sealed unit and should be replaced and not Pressure disassembled, because Sensor of the heavy spring. Park Brake Pump Assembly Driveshaft Type Electric / Hydraulic Activated Control module receives input signals from operator or gear shift position to automatically apply the parking brake. Objective Two

Describe the adjusting procedures for common parking brake systems.. Parking Brake Adjustment Follow manufacturers recommendations for specifications.. Check the condition of the service brakes as they may be part of the park brake system.. Check fluid levels for hydraulically operated park brakes Lubricate all moving parts • Cables are a common cause of problems.. Parking Brake Adjustment Mechanical Linkage Type Apply lever / pedal about 2 to 3 notches. Move the adjusting nut at the end of the cable until a slight Park Brake drag occurs at each Pedal wheel.. Equalizer

Adjustment Screw & Nut Parking Brake Adjustment Hydraulically Operated Check pump reservoir fluid level, ignition key generally off, and parking brake applied..

Inspect: Hydraulic portion of the park system for leakage.. Pressure pump drive belt for proper tension.. Brake shoe to lining clearance.. Parking Brake Adjustment Driveshaft - Internal Shoe Type • Parking brakes will be lost when driveshaft is removed. Transmission Housing

Brake Drum

Drive Shaft

CHOCK THE WHEELS Parking Brake Adjustment Driveshaft - Internal Shoe Type Disconnect brake cable at the drum location.. Adjusting Tool Using suitable tool move the adjuster to adjust lining to drum clearance, through the adjustment opening.. Drum Brake The cable is always adjusted last. Parking Brake Adjustment Driveshaft Type – Internal Shoe Type Park Brake Over Centre ON Hand Lever Lever Design OFF

❶Clevis Pin ❷ ❶ ❷Cam Lever ❸Cam Lever Clevis ❹ ❸ ❹Bellcrank Turning knob on the end of the handle shortens cable, others types adjusted at cam lever clevis. Parking Brake Adjustment Driveshaft Type – External Shoe Type ❶Anchor Adjustment ❷Upper Adjustment ❸Lower Adjustment Return Springs Adjust in sequence: ❶Side Lining To Drum Clearance.. ❷& ❸Top & Bottom Lining To Drum Clearance. Parking Brake Adjustment Disc Type With cable removed, adjust the Pads To Disc Clearance to manufactures specifications.. Connect cable, secure with new cotter pin, adjust cable and check for smooth operation. Parking Brake Adjustment Electric / Hydraulic Activated Propeller Shaft Cam Yoke Lever Bellcrank Clevis

Cam Lever Clevis Bellcrank 1. Chock wheels, ignition key off, inspect for signs of system hydraulic leakage, and inspect or adjust lining-to-drum clearance. Parking Brake Adjustment Electric / Hydraulic Activated 2. Locate parking brake pump assembly and follow manufactures procedure for releasing parking brakes to ensure actuator is releasing the brakes..

3. Loosen jam nut on Jam actuator adjusting nut.. Nut 4. Rotate the actuator cable adjusting nut until it bottoms on the actuator rod, and torque jam nut to specifications. Parking Brake Adjustment Electric / Hydraulic Activated 5. Disconnect bellcrank clevis..A, move bellcrank..B until the shoes lightly contact the drum, adjust bellcrank clevis..A to A the bellcrank’s position.. B 3. Tighten jam nut to manufacturer’s torque specification..

4. Lubricate components, check parking brake operation, ensure shoes are releasing. Objective Three Describe repair procedures for common parking brake systems. Wheel Types Mechanical Linkage Type Some adjustment may be done by the knob of the handle, in the cab.. On other models the knob adjusts the lever over-centre movement.. Cable to The most important check Lever Drum is the brake cable Linkage Knob operation, inspect for freedom of movement between the sheathing and the cable. Hydraulically Operated Parking Brake Control Parking Brake Drum Brake Valve Unitized Valve Wheel Cylinders Parking Brake Reservoir & Pump

Hydro-Max Disc Booster Brake Analyzer Spring- Set Parking Brake Test equipment such as a Park Brake Pump Analyzer, may be needed to test pressures in the hydraulically operated park brakes. Hydraulically Operated Danger Bleed hydraulic system of high pressure before opening any line or fitting..

Apply and release the brakes several times with engine off to relieve high pressure, and crack line carefully to relieve the remaining fluid pressure. 2. Hydraulically Operated Caged Condition Power To HR-1 Park Cylinder Assembly Relay Valve Spring Return Hand Spring Brake Piston

Wedge Power Spring & Roller Caging & Screw Assembly Diaphragm Extreme care should be taken when working with spring brake chambers, cage the spring before removal of spring chamber from vehicle. Driveshaft Type Mechanically Activated Internal Shoe Type Secondary Shoe Front Strut Shoe Hold Primary Shoe Down Clip

Brake Lever Parking Brake Cable Enclosed design retains dirt and dust between lining and drum wearing friction components, inspect for leaks, and clean periodically. Driveshaft Type Mechanically Activated Internal Shoe Type Cable Adjustment Actuating Too Loose Lever

Too Tight

Correct

Ensure cable has freedom of movement and is lubricated. Driveshaft Type Mechanically Activated External Band Type Parking Brake A metal brake band Control with the friction lining are exposed to dirt and Flexible road spray, clean and Brake Drum Cable inspect periodically.. Transmission Disc Type Housing Similar problems and To External solutions as the band Drive Shaft Band type. Driveshaft Type Electric / Hydraulic Activated

Problems can occur in Display Diagnostic three sub-systems, the Port electrical/electronic , hydraulic and mechanical section..

Codes may be retrieved Parking Brake LED from module for diagnostic purposes.. Control Module

Electrical connections are an item to inspect. Driveshaft Type Electric / Hydraulic Activated The actuator can be tested Electric Pump Motor Power Connection for pressured and compared to manufactures specification It is a sealed unit and should be replaced and not disassembled, Pressure because of the heavy Sensor spring. Park Brake Pump Assembly Driveshaft Type Electric / Hydraulic Activated Prior to flushing the hydraulic system be sure to bleed system pressure down before opening any lines or fittings..

Follow manufactures instructions regarding the flushing and filling and use of the proper types of fluids in each individual systems.. A lack of regular inspection and adjustment could affect parking brake operation. The End