770G and 772G Off-Highway Truck: Rear Suspension (Cylinder)

Perform Testing and Adjusting, "Visual Inspections" before you service the suspension cylinders.

The machine must be on level ground when you inspect the suspension cylinder charge. The truck body must be empty. Coast the machine to a gentle stop without using the brakes.

When the rear suspension cylinders are properly charged, the left rear suspension cylinder shows less chrome than the right rear suspension cylinder. The difference is due to the rigid frame and to the weight of the cab.

Note: Both suspension cylinders must be charged at the same time. If only one suspension cylinder needs servicing, perform the procedure on both suspension cylinders.

Check the Height of the Rear Suspension Cylinders

Measure the height of both rear suspension cylinders.

Record the measured height of both rear suspension cylinders.

Compare the current recorded height of the rear suspension cylinders to the previous recorded height of the rear suspension cylinders.Note: The suspension height will be different for each machine.

Purge the Suspension Cylinder Of Oil And Of Nitrogen

Table 1
Tools Needed
Part Number	Description	Qty
175-5507	Nitrogen Charging Group	1
175-7410	Nitrogen Charging Fitting Gp	1
1S-8938	Charging Chucks	2

Note: When you work with the 238-9928 Valve As, the two 1S-8938 Chucks will be needed.

WARNING: Personal injury or death can result from sudden suspension cylinder movement.
Sudden movement, up or down, can cause the clearance above your head to change rapidly.
Read all warning labels on the suspension cylinders before servicing. Do not check the oil in the suspension cylinder until all the nitrogen pressure has been released.
Do not, under any condition, remove valves, cover or plugs from the cylinder unless the rod is fully retracted and all the nitrogen pressure is released.Do not stand under the machine when testing or adjusting the suspension cylinders.

(1) Valve cap
(2) Charging valve(3) Cover

(1) Valve cap
(2) Charging valve(A) Swivel nut

Remove cover (3) from both cylinders. Remove valve caps (1) from the charging valves (2) that are located on the top of each of the rear suspension cylinders.

Turn the tee handles on the 1S-8938 Chuck counterclockwise in order to ensure that the charging valves (2) will not open during installation.

Install the charging hoses to charging valves (2) with 1S-8938 Chuck. The charging hoses will be used to drain oil into an approved container.

NOTICE

Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat products.Dispose of all fluids according to local regulations and mandates.

Turn the swivel nut (A) counterclockwise on charging valve (2) to open charging valve (2) .Note: The valve core is to aid in charging. The valve core is intended as a backup safety for charging valves (2). The valve core is not intended as a primary seal. The swivel nut must be in the closed position prior to attaching the apparatus that is used for charging.

Turn the tee handle on the 1S-8938 Chuck clockwise in order to allow nitrogen to flow through charging valves (2). When the suspension cylinders have bottomed completely, leave the chucks in position for 5 minutes. The pressure in the suspension cylinders will equalize.

Determine the Correct Pin to Pin Dimension

(B) 681.7 mm (26.83853 inch)

(3) Reference line that is level with the bottom surface of the cylinder when purged of oil and nitrogen
(4) Reference line that shows the full oil level
(5) Reference line that shows the full nitrogen charge level without the temperature adjustment(6) Reference line that shows the full nitrogen charge level with the temperature adjustment

Verify the collapsed pin to pin dimension of 681.7 mm (26.83853 inch) (B) .

Position a steel ruler or a thin strip of sheet metal on both of the suspension cylinders in order to measure the rod extension. A magnet can be used in order to mount the measuring tool. Possible magnets include the magnetic plug for the final drive and the magnetic base for a dial indicator. The measuring tool should extend upward. The measuring tool should be parallel to the centerline of the suspension cylinder.

Create reference line (3) on the steel ruler. Reference line (3) should line up with the bottom edge of the cylinder.

Create reference line (4) in order to indicate the guideline for the oil charging procedure. Reference line (4) should be 25.4 mm (1.00 inch) above reference line (3) .

Measure the difference between the outside ambient temperature and the temperature of the service shop. If the temperature difference is less than 11° C (20° F), no adjustment is needed. Line (5) is used when no adjustment is needed. The final pin to pin dimension will be 831.76 mm (32.75 inch).

If this temperature is greater than 11° C (20° F), you will need to adjust the final pin to pin dimension of 831.76 mm (32.75 inch). Add 2.54 mm (0.100 inch) to the pin to pin dimension for every 5.5° C (10° F) of temperature difference. Line (6) is used when an adjustment is needed.Note: Estimate the temperature difference to the nearest 5.5° C (10° F).
Example
Temperature of the service shop ... 50° F
Outside ambient temperature ... -40° F
Difference in temperature ... (50° F) - (-40° F) = 90° F
Additional length for the temperature compensation ... (90° F * .10 in) / 10° F = .90 in
Corrected guidelines for the nitrogen charging procedure ... 831.76 mm + 23.1 mm (.90 inch) = 854.86 mm (33.656 inch)

Oil Charging Procedure

Table 2
Tools Needed
Part Number	Description	Qty
8T-5320	Hydraulic Test Group	1
9U-5617	Oil Refill Pump	1

Note: Ensure that the cylinders have been purged of nitrogen and oil. The collapsed pin to pin dimension is 831.76 mm (32.75 inch).

Rear brake slack adjuster

Note: Assemble an appropriate charging hose from 8T-5320 Hydraulic Test Group .

Connect the charging hose to 1S-8938 Chuck .

Connect the charging hose to the pressure tap on the rear brake slack adjuster. Refer to Illustration 5 in order to view the location of the pressure port. The slack adjuster is located on top of the rear axle housing.

(1) Valve cap
(2) Charging valve
(3) Reference line that is level with the bottom surface of the cylinder when purged of oil and nitrogen
(4) Reference line that shows the full oil level
(5) Reference line that shows the full nitrogen charge level without the temperature adjustment(6) Reference line that shows the full nitrogen charge level with the temperature adjustment

(1) Valve cap
(2) Charging valve(A) Swivel nut

Connect the 1S-8938 Chuck to charging valves (2) .

Start the engine.

Engage the manual retarder.

Turn the tee handle on the 1S-8938 Chuck clockwise in order to open charging valve (2) .

Turn swivel nut (A) counterclockwise in order to open charging valve (2) .

Inject oil into the suspension cylinder until the line (4) is level with the bottom of the cylinder. The correct pin to pin dimension is 912 mm (35.9 inch) prior to any required adjustments from temperatureIf necessary, purge the air from the oil by opening the second charging valve (2). Add oil to the cylinder until oil flows through the second charging valve (2) without air in order to ensure proper performance of the cylinder.

Turn the tee handle on the 1S-8938 Chuck counterclockwise in order to close charging valve (2) .

Turn swivel nut (A) clockwise in order to close charging valve (2) .

Disengage the manual retarder.

Stop the engine.

After the charge pressure has returned to zero, use the quick couplers to remove the charging hoses.

Oil Charging Procedure That Uses The Optional 9U-5617 Oil Refill Pump

Table 3
Tools Needed
Qty	Part Number	Description
1	9U-5617	Oil Refill Pump
2	1S-8938	Charging Chucks



Illustration 8	g02407236
(1) Valve cap (2) Charging valve (3) Reference line that is level with the bottom surface of the cylinder when purged of oil and nitrogen (4) Reference line that shows the full oil level (5) Reference line that shows the full nitrogen charge level without the temperature adjustment(6) Reference line that shows the full nitrogen charge level with the temperature adjustment

Note: Use SAE 10W oil with a service classification of CH for the oil charging procedure.

The charging hoses and the 1S-8938 Chucks should be connected to charging valves (2). Open the shutoff valves. Adjust the air pressure on the regulator. The air pressure must not exceed 860 kPa (125 psi).

Turn the check valves on the 1S-8938 Chucks clockwise to open charging valves (2) .

Turn swivel nut (A) counterclockwise to open charging valves (2) .

Inject the oil into the suspension cylinder until reference line (4) lines up with the bottom surface of the cylinders. Line (4) is 25.4 mm (1.00 inch) above line (3) .Note: If one suspension cylinder reaches reference line (4) before the other suspension cylinder, close the shutoff valve for that suspension cylinder. Continue injecting oil into the other suspension cylinder until the bottom of the cylinder lines up with reference line (4) .

Close the shutoff valves. Turn off the air pressure at the regulator. Turn the check valves on the 1S-8938 Chuck counterclockwise to close charging valves (2) .

Turn swivel nut (A) clockwise to shut charging valves (2) .

After the pressure has returned to zero, use the quick couplers to remove the charging hoses. If the quick couplers are not available, you may need to remove the 1S-8938 Chucks .

Nitrogen Charging Procedure

Table 4
Tools Needed
Part Number	Description	Qty
175-7410	Auxiliary Fitting Group	1
175-5507	Nitrogen Charging Group	1
1S-8938	Charging Chuck	2

WARNING: Dry nitrogen is the only gas approved for use in the suspension cylinders. Charging the suspension cylinders with oxygen gas will cause an explosion. This danger will not happen if nitrogen cylinders with standard CGA (Compressed Gas Association, Inc.) Number 580 Connections are used.
When you order nitrogen gas, be sure that the cylinders are equipped with CGA No. 580 Connections. Do not use color codes or other methods of identification to tell the difference between nitrogen cylinders and oxygen cylinders.Never use an adapter to connect your nitrogen charging group to a valve outlet used on both nitrogen, oxygen or other gas cylinders. Be sure you use dry nitrogen (99.8% purity).

Attach the 175-5507 Nitrogen Charging Group and the 175-7410 Nitrogen Charging Fitting Gp to charging valves (2) at each suspension cylinder.Note: To prevent oil flow into the charging hoses, do not open the charging valves at this time.

Adjust the nitrogen regulator in order to provide 2413 kPa (350 psi).

Open the shutoff valves in order to allow nitrogen to flow to the 1S-8938 Chucks. Turn the tee handles on the 1S-8938 Chucks clockwise to open the charging valves (2). Nitrogen will flow to the charging valves (2). The cylinders will extend until line (5) is level with the bottom of the cylinders.Note: If one suspension cylinder has extended to the correct amount before the other suspension cylinder, close the shutoff valve for that suspension cylinder. Continue allowing nitrogen into the other suspension cylinder until the correct extension has been reached.

The suspension cylinders have extended so that line (5) or line (6) are level with the bottom of the cylinders. After the suspension cylinders have extended, close both of the shutoff valves. Turn the tee handles on the 1S-8938 Chucks counterclockwise.

Turn the swivel nut clockwise on charge valve (2) to closes the charging valves (2) .

Turn off the nitrogen pressure at the supply tank.

Remove the 175-5507 Nitrogen Charging Group and the 175-7410 Nitrogen Charging Fitting Gp .

Install valve caps (1) on charge valve (2) .

Tighten valve caps (1) to a torque of 2 N·m (18 lb in) to 3 N·m (27 lb in).

Install cover (3) to each suspension cylinder.

After the suspension cylinders have been properly charged, measure the pin to pin dimension. Record this value. Use this recorded value as a reference when the rear suspension cylinders are inspected.

Operate the machine through a cycle and check the ride height. If the ride has changed, adjust the nitrogen pressure until the correct ride height is reached. Record the final ride height and pressure.Note: The left and right pressures may not be exactly equal. Typically, pressures will be within 150 kPa (22 psi) of each other on the rear. Ride heights may vary 10 mm (0.4 inch).

MARYGAR