986K Large Wheel Loader Systems Caterpillar

Piston Pump (Steering) High Pressure Stall - Test and Adjust

Usage:

986K MH8

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Personal injury or death can result from escaping fluid under pressure.
Escaping fluid under pressure, even a very small pin-hole size leak, can penetrate body tissue and cause serious injury and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury.

Always use a board or cardboard when checking for a leak.

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NOTICE

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.

Specifications

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Table 1
Steering Pump Pressure
Pump Pressure	Setting
High-Pressure Cutoff (High Idle)	27600 ± 350 kPa (4003.0 ± 51.0 psi)

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Illustration 1	g06275281
(3) Pressure and flow compensator valve (4) Adjustment screw for the pressure compensator

Introduction

This information includes the following test:

High-Pressure Cutoff

This information includes the following adjustment procedure:

Adjustment Procedure (High-Pressure cutoff)

Required Tools

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Illustration 2	g02571852
Tooling (A) 198-4240 Digital Pressure Indicator Gp

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Table 2
Item	Qty	Part No	Description
A	–	198-4240	Digital Pressure Indicator Gp
A1	1	198-4234	Digital Indicator
A2	1	198-4237	Pressure Sensor Gp (0 to 3,445 kPa (0 to 500 psi))
A2	1	198-4238⁽¹⁾	Pressure Sensor Gp (0 to 34,450 kPa (0 to 5,000 psi))
A2	1	198-4239	Pressure Sensor Gp (0 to 41,368 kPa (0 to 6,000 psi))
A2	1	251-9600⁽²⁾	Pressure Sensor Gp (0 to 68,900 kPa (0 to 10,000 psi))
A3	1	198-4236	Adapter Cable As

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⁽¹⁾	This sensor must be purchased separately. The sensor is not included in the 198-4240 Digital Pressure Indicator Gp
⁽²⁾	This sensor can only be used on large diameter pressure taps like 6V-3965 Fitting.

Test Preparation

Refer to Testing and Adjusting, "Machine Preparation for Troubleshooting".

Refer to Testing and Adjusting, "System Pressure Release".

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Illustration 3	g03342031

Move steering frame lock to the LOCKED position.
Engage the parking brake. Move the transmission direction selector to the NEUTRAL position.

Test Procedure

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Illustration 4	g06275289
Steering Pump (G5) Pressure tap for the steering pump pressure

Attach a 41368 kPa (6000 psi) pressure sensor to pressure tap (G5). Pressure tap (G5) is located on the left side of the machine.
Start the engine. Operate the engine at high idle. Continuously stall the RACK BACK function while simultaneously raising the lift arms at full speed. When the lift arms are almost raised, cycle the tilt cylinder almost to the FULL DUMP position. Then move the tilt cylinders to the full RACK BACK position. Continuously stall the RACK BACK function and simultaneously lower the lift arms back to the ground level position. Without stalling the RACK BACK function, cycle the lift function to raise the lift arms fully. Then lower the lift arms in order to allow the pump to operate at low-pressure briefly and circulate oil through the system. Repeat this process in order to increase the temperature of the oil to normal operating temperature.
After the oil has reached normal operating temperature, position the bucket and any attachments slightly off the ground. Run the engine at high idle.
Note: During the following step, do not keep the steering pump at stall condition for more than 10 seconds. If necessary, release the steering wheel and wait for 30 seconds before you repeat the step.
Move the STIC control to the FULL Left or Full Right position in order to obtain a reliable pressure reading.
Record the pressure reading on the pressure gauge. The reading should be 27600 ± 350 kPa (4003.0 ± 51.0 psi).
Adjust the pressure compensator valve if the steering system pressure is not correct.
Stop the engine. Lower the bucket and any attachment to the ground.
Remove the hydraulic line and the pressure gauge from pressure tap (1).

Adjustment Procedure (High-Pressure Cutoff)

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Illustration 5	g06275281
(3) Pressure and flow compensator valve (4) Adjustment screw for the pressure compensator

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Illustration 6	g02923442
(4) Adjustment screw for the pressure compensator (5) Pressure compensator spool (6) Spring (7) Locknut

Remove the cover from the adjustment screw (4). Loosen locknut (7). Turn the adjustment screw (4) clockwise in order to increase the high-pressure stall. Turn the adjustment screw (4) counterclockwise in order to decrease the high-pressure stall. One turn of the adjustment screw equals approximately 2800 kPa (406 psi).
After you turn the adjustment screw (4), tighten locknut (7) to a torque of 21 N·m (16 lb ft).
Replace the cover on adjustment screw (4).