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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. |
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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the work tools have been lowered to the ground, and the oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand. |
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| NOTICE |
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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, "Caterpillar Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates. |
| REQUIRED TOOLS | ||
| Part Number | Description | Quantity |
| 8T-0859 | Gauge 0 to 25000 kPa | 1 |
| 177-7860 | Hose Assembly | 1 |
| 6V-4143 | Coupler | 2 |
| 6V-3989 | Test Fitting | 1 |
- Stop the engine. Engage the parking brake. Depress the brake pedal several times in order to remove all oil pressure from the brake circuit.
- Install one 6V-4143 Coupler to each end of a 177-7860 Hose Assembly. Install the 6V-3989 Test Fitting to the 8T-0859 Pressure Gauge. The pressure gauge has a range of 0 to 25000 kPa (0 to 3600 psi). Install the pressure gauge to one end of the hose assembly. Install the other end of the hose assembly to pressure tap (1) .
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| Illustration 1 | g00727811 |
Location of the pressure tap for machines with the following serial numbers (6XR1-18257SR1-11998CR1-20469AR1-599) | |
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| Illustration 2 | g00729743 |
Location of the pressure tap for machines with the following serial numbers (6XR1826-UP7SR1200-UP8CR2047-UP9AR600-UP) | |
- Position the pressure gauge in order for the operator to view the gauge while the machine is operated.
- Start the engine. Allow the accumulators to fully charge to the cut-out pressure.
The pressure gauge should read 14134 ± 1034 kPa (2050 ± 150 psi) for the following serial numbers: (6XR1826-UP7SR1200-UP8CR2047-UP9AR600-UP).
The pressure gauge should read 15000 ± 700 kPa (2175 ± 100 psi) for the following serial numbers: (6XR1-18257SR1-11998CR1-20469AR1-599).
When the accumulators are fully charged and the hydraulic oil pressure has reached the cut-out pressure, stop the engine.
- Record the cut-out pressure. If the cut-out pressure for the accumulator was not within specifications, then replace the accumulator charging valve.
- Turn the engine start switch to the RUN position but do not start the engine.
- Depress the service brake pedal. Pause briefly before you depress the brake pedal again. The pressure should drop. Continue to depress the brake pedal. Document the depressions to the brake pedal. The pressure should continue to slowly drop with each depression of the pedal.
- When the hydraulic oil pressure is below the cut-in pressure, the low brake pressure indicator on the dash should activate. You should have depressed the brake pedal at least six times. This will indicate if the switch for low brake pressure is operational.
- Continue to depress the brake pedal. Pause briefly before you depress the brake pedal again. Continue to document the depressions to the brake pedal. Continue to watch the pressure gauge. The hydraulic oil pressure will slowly decrease with each depression of the brake pedal. Then, there will be a quick drop in the hydraulic oil pressure. This is the accumulator precharge pressure.
The pressure gauge should read 6900 kPa (1000 psi) for the following serial numbers: (6XR1-18257SR1-11998CR1-20469AR1-599). The pressure gauge should read 3445 kPa (500 psi) for the following serial numbers: (6XR1826-UP7SR1200-UP8CR2047-UP9AR600-UP).
- If the accumulator precharge pressure is not within specifications, then adjust the setting. For the proper procedure, refer to Service Manual Module, SENR1223, "Brake Accumulator - Test and Charge".
- If the cut-out pressure is within the specification, remove the test equipment. Install the dust cap.