938H Wheel Loader and IT38H Integrated Toolcarrier Hydraulic System Caterpillar

Relief Valve (Line) - Test and Adjust

Usage:

938H JKM

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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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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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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, "Caterpillar Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates.

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Table 1
Required Tools
Part Number	Description	Quantity
8T-5320 ⁽¹⁾	Hydraulic Test Group	1
1U-5481	Pressure Gauge Group	1
1U-5482	Pressure Adapter Group	1
4C-6486 ⁽²⁾	Stand	2
8S-7641 ⁽²⁾	Tube	2
8S-8048 ⁽²⁾	Saddle	2
8S-7615 ⁽²⁾	Pin	2
8T-0860	Pressure Gauge	4

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^( 1 )	The 198-4240 Digital Pressure Indicator is also available.
^( 2 )	Optional tooling

Machine Preparation

Park the machine on a surface that is smooth and level. Move away from other operating machines and away from personnel. Lower the work tool to the ground. Turn the engine start switch to the OFF position.

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Illustration 1	g01402670

Place the steering frame lock in the LOCKED position.

Start the engine. Run the engine at high idle. Operate the control levers and move all the cylinders in order to increase the temperature of the hydraulic oil to normal operating temperature. Normal operating temperature is between 54 °C (130 °F) and 82 °C (180 °F).

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Illustration 2	g00384713

Position the lift arms on the stands. This will improve access to the relief valves.

Turn the engine start switch to the OFF position.

Release the pressure from the hydraulic system. Refer to Testing and Adjusting, "System Pressure - Release".

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Illustration 3	g01411155

Remove the front guard in order to access the main control valve.

Relief Valve Pressures and Locations

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Table 2
Settings for the Line Relief Valves
	Head End	Rod End
Tilt cylinder 938H	31000 ± 350 kPa (4500 ± 50 psi)	31000 ± 350 kPa (4500 ± 50 psi)
Tilt cylinder IT38H	9000 ± 350 kPa (1300 ± 50 psi)	28000 ± 350 kPa (4050 ± 50 psi)
Auxiliary cylinder	22100 ± 350 kPa (3200 ± 50 psi)	22100 ± 350 kPa (3200 ± 50 psi)
Auxiliary circuit (fourth function)	22100 ± 350 kPa (3200 ± 50 psi)	22100 ± 350 kPa (3200 ± 50 psi)

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Illustration 4	g01411157
Two-function main control valve (top view) (A) Line relief valve for the head end of the tilt cylinder (B) Line relief valve for the rod end of the tilt cylinder

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Illustration 5	g01411158
Two-function main control valve with ride control (top view) (A) Line relief valve for the head end of the tilt cylinder (B) Line relief valve for the rod end of the tilt cylinder

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Illustration 6	g01411159
Three-function main control valve (top view) (A) Line relief valve for the head end of the tilt cylinder (B) Line relief valve for the rod end of the tilt cylinder (C) Line relief valve for the head end of the auxiliary cylinder (D) Line relief valve for the rod end of the auxiliary cylinder

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Illustration 7	g01411160
Three-function main control valve with ride control (top view) (A) Line relief valve for the head end of the tilt cylinder (B) Line relief valve for the rod end of the tilt cylinder (C) Line relief valve for the head end of the auxiliary cylinder (D) Line relief valve for the rod end of the auxiliary cylinder

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Illustration 8	g01411161
Main control valve with fourth function (top view) (A) Line relief valve for the head end of the tilt cylinder (B) Line relief valve for the rod end of the tilt cylinder (C) Line relief valve for the head end of the auxiliary cylinder (D) Line relief valve for the rod end of the auxiliary cylinder (E) Line relief valve for the head end of the auxiliary circuit (fourth function) (F) Line relief valve for the rod end of the auxiliary circuit (fourth function)

Testing and Adjusting Line Relief Valves

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Illustration 9	g01411199
Right side of articulation joint (1) Main hydraulic pressure tap

Attach a 8T-0852 Pressure Gauge to pressure tap (1) . Refer to Illustration 9.

Place the transmission in the NEUTRAL position and run the engine at high idle. You will need to record the steady rpm of the engine.

Raise the bucket or the work tool off the ground. Move the work tool to the full RACK BACK position. The position of the cylinder rod (rods) will depend on the machine that is being tested.
Note: In the following steps, do not keep the tilt control lever in the ENGAGED position for more than ten seconds while the pressure is at the line relief valve pressure setting. This may cause rapid heating of the hydraulic oil.

Place the transmission in the NEUTRAL position and run the engine at high idle.

Move the tilt control lever halfway between the RACK BACK position and the HOLD position. Slowly move the tilt control lever to the full RACK BACK position. The engine speed will stabilize after five seconds. Check the engine rpm. Compare the current rpm reading to the rpm reading that was obtained in Step 2. The current RPM reading should not be more than 20 RPM lower than the reading that was obtained in Step 2. If the current rpm reading is more than 20 rpm lower then an adjustment is needed. Then proceed to Step 8.

Use Step 6.a for 938H Wheel Loaders. Use Step 6.b for IT38H Integrated Toolcarriers.
1. For the 938H, set the engine speed to high idle. Move the tilt control lever halfway between the DUMP position and the HOLD position. Slowly move the tilt control lever to the full DUMP position. The engine speed will stabilize after five seconds. Compare the rpm reading to the rpm reading that was obtained in Step 2. The current RPM reading should not be more than 20 RPM lower than the reading that was obtained in Step 2. If the current rpm reading is more than 20 rpm lower then an adjustment is needed. Then proceed to Step 8.
1. For the IT38H, set the engine speed to low idle. Move the tilt control lever halfway between the DUMP position and the HOLD position. Slowly move the tilt control lever to the full DUMP position. The engine speed will stabilize after five seconds. The pressure gauge reading should be 9000 ± 690 kPa (1300 ± 100 psi). If the reading is not within the range that is listed the relief valve will need to be adjusted. Refer to Step 8.

The testing of the line relief valves for the tilt function is complete. Repeat Step 2 through Step 6 for each auxiliary function that will be tested.

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Illustration 10	g01411246
Line relief valve (typical example) (2) Locknut (3) Adjustment screw

Adjust the line relief valve. Refer to Illustration 4 through Illustration 8 for the correct main control valve for the machine. The illustrations will show the locations of the line relief valves.
1. Turn the engine start switch to the OFF position.
1. Loosen locknut (2) . Turn adjustment screw (3) clockwise in order to increase the relief valve setting. Turn adjustment screw (3) counterclockwise in order to decrease the relief valve setting. The adjustment screw should only be turned one quarter of a turn. Repeat Step 2 through Step 6 after making the adjustment.
  Note: Always turn adjustment screw (3) in a clockwise direction in order to adjust the pressure. This will compensate for any internal friction inside the valve that would oppose the setting of the bias spring. . For example, if the adjustment screw needs to be turned counterclockwise by a quarter of a turn in order to decrease the pressure, turn the adjustment screw counterclockwise by one full turn. Then, turn the adjustment screw clockwise by a quarter of a turn.
1. After adjustment screw (3) is turned for an adjustment, tighten locknut (2) . Tighten locknut (2) to a torque of 61 ± 6 N·m (45 ± 4 lb ft).

Replace the relief valve if the test values do not fall within the specified values that are listed above.

Adjust the signal relief valve to the correct pressure. Refer to Testing and Adjusting, "Relief Valve (Signal) - Test and Adjust".

When the test is finished, position the lift arms on the stands. Turn the engine start switch to the OFF position. Install the front guard over the main control valve.