AUTOMATIC BLADE CONTROL With Engine Running Caterpillar

With Engine Running
1.1. Check and Calibrate Grade and Slope Controls
2.1. Servo Valve Adjustment (Type One)
3.1. Servo Valve Adjustment (Type Two)
4.1. Servo Valve Filter
5.1. Check Cutting Edge Wear
6.1. Tape or Chain Adjustment Check
7.1. Adjustment
1. Before checking, calibrating or operating the Automatic Blade Control, operate as a manual grader for 10 to 15 minutes. Cycle lift cylinders a few times to warm oil and purge trapped air.
2. With engine running and blade lift cylinders retracted, check hydraulic oil level. Oil level must be at least 1/4 inch above ADD mark in sight gauge. Add oil if necessary.

Check and Calibrate Grade and Slope Controls

1. Never zero adjust meters with the power switch in the ON position. With power switch in OFF position, adjust meters to read zero. Meters are adjusted by rotating screw (1).

2. Power switch ON. Always allow 3 minutes for warm up before calibrating slope control. Selector in manual position, slope and grade switches in OFF position.

3. Motor grader should be reasonably level and moldboard at right angle (90°) to frame.

4. Position blade in vertical position at about 8 or 9 on the blade tip indicator.


Do not adjust the circle level on the rear of the circle unless resetting it with respect to circle. Leveling it to the cutting edge will introduce errors in operation. Errors will increase as blade is circled to higher angles.

5. Center leveling bubble, to level circle, by manipulating lift arms.

6. If machine has been used check cutting edge for wear. (See topic Cutting Edge Wear, page 19).

7. With slope control dial at zero, slope meter should read zero. Dial drag can be adjusted with 2 set-screws on the dial.

NOTE: Be sure the dial is in the correct zero location when calibrating the slope control. The slope control dial can be rotated 1 revolution counterclockwise and 2 revolutions clockwise from the zero position. Be sure physical stops are encountered when locating this position. The 2nd revolution in the clockwise direction is not used.

8. If the meter is off to either side, loosen dial thumbscrew.

9. Bring meter back to zero by turning hub with a flat tool, while holding dial at zero.

10. Turn grade and slope selector to the left slope position.

11. Turn slope switch ON. Grade switch should be OFF.

12. Raise left lift arm with manual control.

13. Watch the slope meter and left cylinder. Meter should return to zero when cylinder movement stops. There should be no further movement.

14. If meter needle does not stay within center black band, adjust left servo valve.

15. Remove valve protection cover.

Servo Valve Adjustment (Type One)

16. Insert a hex head wrench (1) in the small hole in the valve body. Loosen the setscrew enough to allow bushing pin to turn (not more than 1/8 turn 45°).

17. Insert short, narrow blade screwdriver (2) in the adjusting hole of valve body. Adjust the bushing pin until the slope meter reads zero and cylinder movement stops.

18. Lock setscrew. Make sure setscrew bottoms against bushing. Do not overtighten.

Servo Valve Adjustment (Type Two)

16. Loosen the self-locking nut with a 3/8 inch offset box wrench. Do not remove nut. Loosen only enough to allow movement of the null adjuster pin.

17. Insert a 3/32 inch hex head screw wrench in the null adjuster pin and turn until meter is zeroed and cylinder movement stops.

18. To prevent null adjuster pin rotation after null has been obtained, hold the pin with the hex head screw wrench while tightening the lock nut.

19. Turn grade and slope selector to the right slope and repeat steps 11 through 18 for the right side.

Servo Valve Filter

Service servo valve filter only when filter change light is on.

Replace filter if filter change light is on constantly or blinks continuously after hydraulic oil is warm.

Check Cutting Edge Wear

The procedure for checking and calibrating slope control is based on using the circle for level reference, assuming the moldboard is parallel to the circle. Whenever calibrating slope control it may be necessary to adjust this with shims between blade bracket and moldboard side shift rail wear plates. This does not allow for uneven cutting edge wear. After slope control has been calibrated using circle bubble, check for cutting edge wear.

Level entire length of cutting edge with a carpenter's level or slope board.

2. Set grade and slope selector on MANUAL. Set slope dial on zero if cutting edge was leveled.

3. If slope meter is off to either side, turn slope dial until meter reads zero.


DO NOT adjust the circle level on the rear of the circle UNLESS resetting it with respect to circle. Leveling it to cutting edge will introduce errors in operation. Errors will increase as blade is circled to higher angles.

Tape or Chain Adjustment Check

1. Park motor grader on a surface where it is level both laterally and longitudinally with the blade positioned at 90° to the longitudinal axis and centered in the circle.

2. Disconnect center shift link and position where it cannot interfere with the drawbar frame when the frame is raised.

3. With the engine running, turn the control console power switch on. Set the slope and grade switch on MANUAL.

4. Manually level the circle according to circle bubble with blade square (at 90° to frame).

5. Slope meter should read zero as described on page 14.

6. Place level on cutting edge and mark bubble position. Raise drawbar as high as practical and bring level bubble back to original position.

NOTE: The slope meter should read zero.

If the slope meter does not read zero the ball resolver chain requires adjustment.

Error in this adjustment causes slope error at blade angles other than 90° to the frame.


1. Remove the rubber cover between the transfer gear and cam drive housing and the end of the drawbar frame bolt (ball).

2. Loosen the lock screw on the clamp and turn the clamp in the direction necessary to return the meter pointer to zero.

3. If the pointer is left of zero, turn the clamp counterclockwise.

4. Tighten the clamp lock screw.


Do not turn the clamp too many turns counterclockwise or the key slot in the screw will disengage with the key in the shaft in the cam drive housing.

5. Install the rubber cover.
6. Lower circle and connect the center shift link.