621H, 623H and 627H Wheel Tractor-Scrapers Power Train Caterpillar

Specifications

Introduction

This test will verify that the main relief valve is set to the correct pressure setting.

Required Tools

Illustration 1	g02571852
Tooling (A) 198-4240 Digital Pressure Indicator Gp

Test Preparation

1. Operate the machine until the transmission oil temperature reaches normal operating temperature.

2. Stop the machine on a hard, level surface. Move the transmission control lever to NEUTRAL. Lower the bowl. Stop the engine. Engage the parking brake.
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   Illustration 2	g02609402
   Rear of the Tractor, Left Side of the Transmission (1) Test port for the main relief valve

3. Remove dust cap from test port (1) for the transmission charge pump. Connect Tooling (A) to test port (1).

Test Procedure

1. Start the engine. Release the parking brake. Depress the service brake control (pedal) and keep the pedal down.

2. Run the engine at LOW IDLE in NEUTRAL. The pressure must be a minimum of 2827 kPa (410 psi).

3. Run the engine at HIGH IDLE in NEUTRAL. The maximum relief valve pressure must be 3034 kPa (440 psi) to 3241 kPa (470 psi). If the pressure reading is correct, continue to Step 1. If the pressure reading is not correct, stop the engine. Complete the following procedure.

Adjustment Procedure

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Illustration 3	g02609458
View from rear of tractor

1. Remove the top cover from the transmission (1).
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   Illustration 4	g02609460
   Transmission control valve

2. Remove cover for adjustment screw (2). Turn adjustment screw (2) clockwise to increase transmission pressure. Turn adjustment screw (2) counter clockwise to reduce transmission pressure.

3. After the main relief pressure has been adjusted, the individual transmission clutch pressures will need to be rechecked.