SUPPORT AS 8R8721 - Caterpillar

Table 1
Required Tools    
Part Number     Part Description     Qty    
6V-3079     Hose     1    
6V-4142     Fitting (Test)     1    
6V-4143     Coupler     1    
6V-4144     Coupler     1    
8T-0859     Pressure Gauge     1    
Personal injury or death can result from sudden machine movement.Sudden movement of the machine or release of oil pressure can cause injury to persons on or near the machine.To help prevent possible injury or death, refer to the information in Testing and Adjusting, "Machine Preparation for Troubleshooting".
Oil pressure from the brake pump can be checked at the test fitting on the check and pressure reducing valve. The check and pressure reducing valve is located under the hinged cover at the rear of the cab.
Illustration 1 g00669411
Test point for oil pressure from the brake pumpNote: Make sure that the oil is at operating temperature before you perform this test.Procedure
Install 6V-4144 Coupler onto 8T-0859 Pressure Gauge (0 to 25000 kPa (0 to 3600 psi)).
Connect the pressure gauge to the test point with 6V-4142 Fitting (test), 6V-4143 Coupler and 6V-3079 Pressure Hose Assembly .
Start the engine with the parking brake engaged. Run the engine at low idle with the transmission in the NEUTRAL position.
The pressure reading on the pressure gauge should register 20400 350 kPa (2950 50 psi).
Increase the engine speed to high idle. The pressure gauge reading should remain constant.A high pressure reading on the pressure gauge of 24100 kPa (3500 psi) would indicate that the relief valve in the check and pressure reducing valve has been activated. This would indicate that the pressure and flow compensator valve of the brake pump has failed or that the setting has been set too high.
Depress the pedal for the service brake control. The oil pressure from the brake pump should decrease to 12000 1700 kPa (1750 250 psi). The oil pressure should recover within two or three seconds.A problem with the brake pump would be indicated if the reduced pressure reading from the brake pump failed to recover within three seconds.
When the test is complete, stop the engine and remove the test equipment.