Sunday, December 2, 2012

777F Off-Highway Truck Suspension Cylinder Testing and Adjusting

General Information

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.

The suspension system on the machines consists of four suspension cylinders. When the suspension cylinders are charged with the proper amount of oil and nitrogen, the suspension system should provide an easier ride for the operator.

Note: These procedures are intended to be used in order to maintain the correct suspension cylinder charge. See Testing And Adjusting, "Suspension Cylinder Oil Requirements" for procedures for assembly of a new suspension cylinder or of a rebuilt suspension cylinder.

Conditions For Servicing

Service your suspension cylinders when any of the following conditions exist:

A fault code that indicates that there is low pressure in a suspension cylinder is present.
Most of the chrome is wiped off by the wiper seals during normal operation.
Suspension cylinder shows signs of leakage.
The ride is harsh.
The struts are at full extension when the truck is empty.

In the analysis of a problem in the suspension cylinders, each suspension cylinder operates as a separate unit. Also, when the left rear suspension cylinder is low, the right front suspension cylinder should be high due to the rigid machine frame. For the same reason, when the right rear suspension cylinder is low, the left front suspension cylinder should be high.

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

Visual Inspection

A visual inspection of each suspension cylinder is the first step in the analysis of a problem. Make sure that the machine is on level ground. Do the inspection on an empty machine while the engine is stopped.

Check each suspension cylinder for oil leaks around the seals and around the valves.

Check each suspension cylinder for nitrogen leakage. Detection of leaking nitrogen is very difficult. A solution that consists of soap and of water can be used to detect leaks. Make sure that there is no leakage around the valve cores and around the valve bodies. Make sure that the valve caps are in place. Make sure that the valve caps are tightened to 2 to 3 N·m (18 to 27 lb in).

Check for leakage at the O-rings that are located under the manifold and under the pressure sensor. Check for leakage at the O-rings that are located under the protective plates that are on the head. These protective plates cover some of the head bolts in order to prevent removal of the head while there is pressure in the suspension cylinder.

Friction between the rod and the lower wear band may cause a dark stain to appear on the chrome of the suspension cylinder. This stain does not affect the wear life of the suspension cylinder. You can polish the chrome in order to remove this stain. Eventually, the wear band should become soaked by oil and by grease and the blackening should decrease.

Suspension Cylinder Oil Requirements

When you rebuild a suspension cylinder or when you assemble a suspension cylinder, use these oil requirements.

Table 1
Oil Requirements For Suspension Cylinders
Model Family	Front Suspension Cylinder	Rear Suspension Cylinder
769, 771	13.8 L (3.6 US gal)	11.2 L (3.0 US gal)
770, 772	13.8 L (3.6 US gal)	11.2 L (3.0 US gal)
773, 775	12.8 L (3.4 US gal)	12.0 L (3.2 US gal)
776, 777	34.5 L (9.1 US gal)	16.3 L (4.3 US gal)
784, 785	47.6 L (12.6 US gal)	25.9 L (6.8 US gal)
789	60.1 L (15.9 US gal)	35.6 L (9.4 US gal)
793	74.5 L (19.7 US gal)	35.6 L (9.4 US gal)
797 ⁽¹⁾	119 L (31.4 US gal)	48.5 L (12.8 US gal)
797 ⁽²⁾	104 L (27.5 US gal)	48.5 L (12.8 US gal)
797B	104 L (27.5 US gal)	48.5 L (12.8 US gal)

^( 1 )	5YW1-237
^( 2 )	5YW238-Up

After the suspension cylinder contains the required amount of oil, install the suspension cylinder. After this has been done, the normal charging procedures can be performed.

MARYGAR