621 TRACTOR-SCRAPER Moving The Tractor-Scraper Caterpillar

1. Fasten seat belt.

2. Push emergency brake button. Do not move machine until low air pressure light goes off and brake button remains depressed. If equipped with emergency and parking brake system, move lever to EMERGENCY position for at least 3 seconds before moving lever to RELEASE. (See page 19 for additional information.)

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Check to be sure area is clear of personnel and obstructions.

3. Depress brake pedal.

4. Pull lever to raise bowl.

NOTE: In an emergency the tractor-scraper can be moved in first gear with the emergency brake applied.

5. Push and turn transmission safety lock to OFF. Pull transmission control lever to first gear for manual transmission. (Move control to desired position on semiautomatic transmissions.)

6. Release brake pedal. Depress accelerator pedal.

Parking/Emergency Brake System

1. If parking brake does not release, move lever to EMERGENCY position. Push governor override button to raise air pressure to 150 PSI (10,5 kg/cm²).

2. Release override button and move lever to RELEASE.

Emergency Stops

If low air pressure warning light comes on, or emergency warning horn sounds, stop the machine immediately.

To stop machine if the service brakes do not; push emergency brake lever to EMERGENCY position.

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Brakes will automatically apply if air pressure drops below safe operating pressure. If the tractor-scraper is stopped on a steep grade by the emergency system, do not release brakes. After an emergency stop, wait until air pressure gauge registers NORMAL before moving the machine. If air pressure gauge will not register NORMAL have the air system checked.

NOTE: In an emergency the tractor-scraper can be moved in first gear with the emergency brake applied. Check condition of brakes before operating machine again.

Changing Gear Speed and Direction

Manual Control Transmission-Upshift progressively, with control lever, to desired speed. Upshift under normal conditions at 2150 to 2200 engine RPM. Engine should operate at 1600 to 2200 RPM. Downshift when engine RPM drops to 1600 to 1700.

Semiautomatic Control Transmission-Upshift manual through second speed. Set control lever at desired speed. Transmission will automatically upshift and downshift between 2nd and the selected speed.

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Improper downshifting can cause sudden reduction in travel speed. Use hydraulic retarders and/or service brakes to reduce speed before entering sharp turns, fill areas and downgrades. Do not move transmission control level with transmission HOLD applied. Never coast downgrade. Keep transmission engaged.