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Hot hydraulic oil under high pressure can remain in the components of the hydraulic system or the power train system after the engine has been stopped. The uncontrolled release of the hydraulic oil can cause sudden machine movement and can also result in the following conditions:
If hydraulic oil penetrates body tissue, the injury must be treated immediately by a doctor who is familiar with this type of injury. Use a board or a piece of cardboard to check for a hydraulic oil leak. Make sure that all of the attachments have been lowered to the ground and that all trapped pressure has been released from the hydraulic system and the power train system. Also, make sure that the hydraulic oil is cool before the removal of any components or lines. Remove the hydraulic 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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Sudden movement or accidental starting of the machine can cause personal injury or death to persons on or near the machine. To prevent personal injury or death, perform the following: Park the machine on a smooth, level surface. Lower the work tool to the ground and engage the parking brake. Stop the engine and remove the key. Block the wheels and install the steering frame lock. |
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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, "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. |
| Pilot Pressure - High Idle | |
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There are two pilot systems that are generated from the fan/brake valve in the hydraulic service center.
- The primary steering pilot system supplies pilot pressure to the steering system.
- The implement/redundant steering pilot system supplies pilot pressure to the implement system and the steering system if the primary steering system fails.
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| Illustration 1 | g02571852 |
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Tooling (A) 198-4240 Digital Pressure Indicator Gp | |
| Required Tools | ||||
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| Tool | Item | Qty | Part No | Description |
| A | 198-4240 | Digital Pressure Indicator Gp | ||
| A1 | 1 | 198-4234 | Digital Indicator | |
| A2 | 1 | 198-4239 | Pressure Sensor Gp
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| A3 | 1 | 198-4236 | Adapter Cable As | |
- Move the machine to a smooth, horizontal location that is away from operating machines and away from personnel.
- Place the transmission direction in the NEUTRAL position.
- Engage the parking brake.
- Lower the work tool to the ground.
- Stop the engine.
- Relieve the pressure in the hydraulic system.
Reference: For more information about relieving the hydraulic pressure, refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.
- Install the steering frame lock.
- Install tooling (A) to test port (1).
- Start the engine and warm up the hydraulics if necessary. The hydraulic oil temperature should be at least
60° C (140° F) . - Increase the engine speed to high idle.
- Observe the pilot pressure on tooling (A), the pressure should be
3500 ± 345 kPa (508 ± 50 psi) . - Lower the engine speed to low idle.
- Stop the engine.
- Remove tooling (A).
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| Illustration 2 | g03728245 |
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Pressure taps located on the left inside wall of the articulated hitch on the front differential lock valve. (1) Implement/ Redundant Steering Pilot Supply Pressure Tap (2) Implement Load Sense Pressure Tap | |
Check complete.
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| Illustration 3 | g06044833 |
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Brake/Fan valve located in hydraulic service center on the right side of machine (A) Fan/brake valve (3) Pressure reducing valve (PRV) | |
Locate the implement/redundant steering pilot pressure reducing valve (PRV) (3) on the side of the fan/brake valve (A) in the service center. Use a hex wrench to loosen the lock-nut and an internal hex wrench to adjust the pilot pressure.
- To increase pressure
- Hold the adjustment screw with the internal hex wrench and loosen the lock-nut
- Turn the adjustment screw inward. A quarter or half turn is often enough to reach the desired setting.
- Holding the adjustment screw, tighten the lock-nut.
- Recheck the pressure to ensure that the pressure is set as desired.
- To decrease pressure
- Hold the adjustment screw with the internal hex wrench and loosen the lock-nut
- Turn the adjustment screw outward first and then, inward to the target pressure. A quarter or half turn is often enough to reach the desired setting.
- Holding the adjustment screw, tighten the lock-nut.
- Recheck the pressure to ensure that the pressure is set as desired.
Note: The last turn of the screw should always be an inward turn, or pressure increase.