621B TRACTOR-SCRAPER Operating Techniques Caterpillar

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1. Reduce travel speed and downshift when approaching cut. Move ejector to the rear. Push cushion-hitch lever to LOCKDOWN.

2. Open apron and lower bowl to desired depth of cut. Shift transmission to 1st or 2nd speed.

3. Regulate apron opening to keep material from piling in front of lip or falling out of bowl.

4. Decrease depth of cut if engine lugs below operating range. Close apron and raise bowl to finish cut.

Raise and lower bowl rapidly to pump in loose material. When finishing in loose material, raise bowl slightly, close apron partially, then raise bowl.

Push Loading

1. Keep moving while pusher tractor is making contact. Push cushion-hitch lever to LOCKDOWN.

2. Keep tractor and scraper in line for efficient push loading.

3. Cut deep as possible without stalling tractor-scraper and pusher.

4. Start raising bowl as soon as it is full.

5. Allow pusher to help machine out of cut area in poor underfoot conditions.

6. Upshift and accelerate to haul travel speed as quickly as possible. Push hitch lever to CUSHION RIDE.

Hauling

1. Move hitch control to CUSHION RIDE. Carry bowl just high enough to clear obstructions.

2. Travel at highest speed practical on level ground.

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NOTICE
Watch for and obey flagmen in traveled areas.

3. Downshift on upgrade before engine speed drops below operating range.

4. Reduce travel speed and downshift when approaching downgrade.

5. Use retarders, if so equipped, and service brakes to control speed on downgrade.

6. Keep engine speed under 2100 RPM on downgrade.

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NOTICE
Keep retarder temperature in normal operating range.

7. In poor footing, engage differential lock. Reduce speed to permit lock to engage if one wheel is spinning.

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Disengage Differential Lock before turning. Turning with lock engaged can be hazardous.

8. Apply individual tractor wheel brakes to maneuver out of soft spots.

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NOTICE
Do not attempt to apply individual wheel brake with differential lock engaged.

Dumping and Spreading

1. Dump and spread material at highest practical travel speed, considering fill and traffic conditions. Approach fill in line with dump area. Lower bowl to desired spread height. Move hitch control to LOCKDOWN.

2. Open apron at start of dump area. Raise and lower apron to loosen sticky material before moving ejector.

3. Move ejector forward after material has fallen from back of apron.

4. Close apron as soon as bowl is empty.

5. Raise bowl gradually to leave fill area smooth. Return ejector to rear.

Return to Cut

1. Move hitch control to CUSHION RIDE. Carry bowl just high enough to clear obstructions.

2. Upshift to travel speed as soon as practical.

3. Keep engine speed under 2100 RPM on downgrade.

4. Use retarders, if so equipped, and proper gear speed to control travel speed.

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NOTICE
Keep retarder temperature in normal operating range.