This section describes some routine procedures you can use to maintain the hydraulic transmis-sion in good operating condition and to identify the overall condition of the transmission. These guidelines include the care of the oil system and minor adjustments you can make to the transmis-sion and control linkage.

In the maintenance of the oil system, the proper oil level is very important. The transmis-sion oil serves to apply clutches and lubricant and to cool the components. Consequently, transmis-sion performance will be affected if the oil becomes aerated. The primary cause of aeration or foaming is either low oil or too much oil in the sump. A low oil level can cause the input pump to cavitate. Too much oil in the sump can introduce oil into the gearing and clutches. This condition can cause aeration, which will overheat the transmission. Aeration can also change the viscosity and color of the oil to a thin milky liquid. These conditions will all cause irregular operation of the unit.

The oil level should be checked daily after the engine has been running for at least 1 hour. The oil level should be maintained at the FULL mark on the dipstick. Every 150 hours (or sooner, depending on the type of duty and environment), the oil and oil filters should be changed. You should refer to the appropriate PMS for the specific procedures and intervals you should use for your unit. Heavy sludge deposits on the oil filter element indicate that the detergency of the oil has been exhausted. When this occurs, the oil change interval should be shortened. The oil filter should always be replaced at the time of the oil change so that any abrasive dust and metal particles can be removed.

When you must change the oil and filter, follow these general procedures:

1. Make sure the transmission has been warmed up to operating temperature.

2. Remove the oil drain plugs from the sump and oil filters and drain the oil. Replace the plugs.

3. Thoroughly clean the transmission strainer assembly. Use a new gasket when you are replacing the cover of the strainer.

Figure 12-5.-Operation of planetary gear assembly.

4. Replace the filter elements. Thoroughly clean the filter shells and use new gaskets (seal rings) with the new filter elements.

5. Before starting the engine, remove the breather and refill the transmission with clean oil (from a clean container) to prevent contamination.

6. When refilling the system, pour enough oil into the transmission to bring the oil level up to the FULL mark on the dipstick. Start the engine

Figure 12-6.-Clutch and reverse-reduction gear assembly.

and let it idle for 2 or 3 minutes with the transmis-sion in neutral. Recheck the oil level and add oil (if necessary) to bring the oil up to the FULL mark on the dipstick. Do not overfill the transmission.

7. Carefully inspect the filter components and cover for oil leakage while the engine is running.

At each oil change, examine the used oil for evidence of dirt or water. If there is evidence of free water, check the cooler for leakage between the water and oil areas. Oil in the water side of the cooler is another sign of leakage. This, however, usually indicates leakage from the engine oil system.

If coolant leaks into the transmission oil system, you must take immediate action to pre-vent malfunction and possible serious damage. Ethylene glycol antifreeze will attack the material that lines the clutch plates. You must immediately disassemble, inspect, and clean the transmission and flywheel assembly. If antifreeze is present, both forward and reverse friction clutch plates must be replaced. The cooler should be repaired or replaced prior to installation of the new or rebuilt transmission.

Metal particles in the oil (except for the minute particles normally trapped in the oil filter) indicate damage has occurred in the transmission. When these particles are found, the transmission and flywheel assembly should be completely disassembled, and all internal and external oil circuits and all other areas where particles could lodge should be cleaned.

In the selector valve linkage assembly, the manual selector lever should move easily and give a crisp detent feel in the forward, neutral, and reverse positions. You should adjust the linkage so that the stops in the shift tower match the detents in the transmission.

Make periodic inspections for bent or worn parts, loose threaded connections, loose bolts, or accumulations of grease and dirt. All moving joints must be kept clean and well lubricated.