621 TRACTOR-SCRAPER Operating Techniques Caterpillar

Operating Techniques
1.1. Loading
2.1. Push Loading
3.1. Dumping and Spreading
4.1. Hauling


1. Reduce travel speed and downshift to 2nd; push cushion-hitch control to LOCKDOWN and check to see that ejector-floor is closed. Maintain high engine RPM while loading.

2. Open apron approximately 15 inches (0,5 m) and lower bowl to desired depth when entering cut.

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. When finishing cut, close apron, then raise bowl.

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 is making contact. Keep tractor-scraper in line with pusher. Cut as deep as possible without stalling machines. Maintain smooth cut area when practical.

2. Raise bowl as soon as it is full. Allow pusher to help machine out of cut area.

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. For better control while spreading, push cushion-hitch lever to LOCKDOWN.

2. Pull apron lever at start of dump area. Push and pull apron lever to loosen sticky material before moving ejector.

3. Pull ejector control after material has fallen from back of apron.

4. Push apron lever when bowl is empty. Pull lever and raise bowl slowly to leave fill area smooth.

5. Push controls to return ejector to rear. Pull cushionhitch lever for CUSHION RIDE (if not engaged) accelerate machine to highest speed practical for return to cut.


Pull cushion-hitch lever to engage CUSHION RIDE. Do not engage CUSHION RIDE on slopes or in sharp turns.

Carry load as low as possible and still clear obstructions. Accelerate to highest practical travel speed.

NOTE: Watch for and obey flagmen.

When shifting back and forth between two highest gears, use the lower gear unless cycle time can be reduced in higher gear.

Reduce travel speed and downshift when approaching downgrade. Use retarder and service brakes as necessary to control speed. Keep engine RPM below 2100 and retarder temperature below 275°F.

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

To maneuver out of soft spots, apply individual tractor wheel brakes. Do not apply individual wheel brakes when differential lock is engaged.


Do not turn with differential lock applied.