12M Series 3, 140M Series 3, 160M Series 3, 140, 150 and and 160 Motor Graders Brake System Air - Purge Caterpillar

Brake System Air - Purge
1.1. Safety Information
2.1. Introduction
3.1. Required Tools
4.1. Machine Preparation
5.1. Perform the Process
6.1. Perform the Kidney Loop Procedure

Safety Information

------ WARNING! ------

Personal injury or death can result if two persons are not used in the following procedure.

------ WARNING! ------

Sudden movement of the machine or release of oil under pressure can cause injury to persons on or near the machine.

To prevent possible injury, perform the procedure that follows before testing and adjusting the brake system.


Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.

Refer to Special Publication, NENG2500, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat products.

Dispose of all fluids according to local regulations and mandates.

------ WARNING! ------

Personal injury can result from improper troubleshooting and repair procedures.

The following troubleshooting and repair procedures should only be performed by qualified personnel familiar with this equipment.

------ WARNING! ------

Do not attempt to disassemble or assemble this machine until you read and understand the disassembly and assembly instructions. Improper disassembly and assembly procedures could result in injury or death.

------ WARNING! ------

Personal injury can result from contact with hot hydraulic oil and from contact with hydraulic oil that is under high pressure.

Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. The hydraulic oil pressure must be released before any service on the hydraulic system is performed or serious personal injury could occur.

Verify that all of the work tools have been completely lowered to the ground. Release the hydraulic oil pressure at the hydraulic tank through the breaker relief valve when the breaker relief valve is cool enough to touch with your bare hand. Verify that the hydraulic oil is cool before you begin to remove any hydraulic components or hydraulic lines.


Before service work is begun, park the machine on a hard level surface. Block the wheels of the machine so unexpected movement will not occur. Unexpected movement of the machine can cause personal injury or death.


This procedure will remove air from the brake system.

Required Tools

Table 1
Required Tooling 
Item  Part Number  Description  Qty 
  Suitable containers 
177-7860(1)  Hose As 
6V-4143(1)  Quick Connect Coupler 
6V-3966  Fitting As 
(1) Assemble into a tool for purging the brakes.

Connect one end of each hose assembly (G) to one quick connector coupling (H).

Machine Preparation

Before you begin this procedure, refer to Testing and Adjusting, "Machine Preparation".

  1. Move the machine to a smooth, horizontal location. Move the machine away from other operating machines and away from personnel. Lower the work tools to the ground and move the parking brake switch to the on ON position. Place chocks in front of the wheels and behind the wheels.

  2. Check the hydraulic tank oil level. Make sure that you maintain the correct oil level in the hydraulic oil tank throughout the air removal procedure.

    Illustration 1g03541282
    View of wheel station with guard installed

  3. Remove the top guard (K) that protects the plumbing at each rear wheel station

  4. Hook up the kidney loop system

    Illustration 2g03541297
    View of wheel station with guard removed

  5. Remove all four purge screws (L) and install four fittings (J)

  6. Attach four black purge hose assemblies that were built previously to fittings (J). Place the other end of the black purge hoses into the hydraulic tank.

Perform the Process

  1. Start the engine and allow the accumulators to charge completely. Then shut off the engine.

  2. Slowly depress the service brake pedal until the accumulators are empty. Then release the pedal.

  3. Start the engine and allow the accumulators to charge. Then shut off the engine

  4. Repeat Step 2 and Step 3 four times.

  5. Fill the hydraulic tank if necessary

Perform the Kidney Loop Procedure

  1. With the purge adapters still securely installed, start the engine.

  2. During the kidney loop procedure slowly depress the service brake pedal to approximately 50% depression and hold for 30 seconds. Then release the pedal. Repeat this process throughout the kidney loop procedure.

  3. When this procedure is complete stop the engine. Remove hoses and fitting assemblies.

  4. Install all four purge screws and tighten all four purge screws.