621H, 623H and 627H Wheel Tractor-Scrapers Braking and Hydraulic Fan System Caterpillar

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Personal injury can result if the machine moves while testing. If the machine begins to move during test, reduce the engine speed immediately and engage the parking brake.

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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.

Specification

Introduction

This test will check the performance of the accumulator charging valve and accumulators.

Required Tooling

Illustration 1	g01623868
Tooling (B)

Preparation for Test

1. Move the machine to a smooth, horizontal location. Move the machine away from other operating machines and away from personnel. Warm up the engine to the normal operating temperature. Place the transmission direction control switch in the NEUTRAL position. Engage the parking brake. Lower the bowl to the ground. Stop the engine and put chocks in front of the wheels and behind the wheels.
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   Illustration 2	g03350092
   Looking up at the shaded belly pan

2. Remove the crank case guard to allow access to the control manifold for the hydraulic fan and brake. Refer to Disassembly and Assembly, KENR8882, "Crank Case Guard - Remove and Install" for the procedure to remove the crank case guard.
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   Illustration 3	g03349558
   View of the control manifold for the hydraulic fan and brake as seen from the front of the tractor.

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   Illustration 4	g03349960
   (1) Test port as seen in a close up view of the control manifold for the fan and brake. Viewed from beneath the tractor.

3. Connect (B) to test port (1)

Perform the Test

1. Start the engine. Run the engine at low idle and place the parking brake switch in the OFF

2. Pump the brake pedal until the cut-in pressure of 13800 ± 520 kPa (2000 ± 75 psi) is reached and allow the accumulators to reach the cut-out pressure of 18000 +1950 - 520 kPa (2610 +285 -75 psi).

3. Immediately shut off the engine and immediately cycle the key back to the ON position

4. Pump the service brakes at a a rate of one second on and one second off. Count the number of brake applications that are required to illuminate the low-pressure warning indicator.

5. Turn the engine key to the start position and operate the engine at low idle and allow the brake accumulators to reach the cut-out pressure. Run the engine at low idle, the machine in park, and the service brakes released. The accumulator pressure shall not decrease from the cut-out pressure to the cut-in pressure in less than 30 seconds.

6. Remove the test equipment (B) and reinstall the dust cover.