Understanding the hydraulic system that is used in the motor home transmission system may be helpful when performing vehicle maintenance. Each type of engine requires a specific hydraulic pump that can be mounted on the engine, or directly onto the transmission. In some instances the hydraulic pump is a combination for the hydraulic fans and power steering. On selected models two separate pumps are used.

If the temperature gauge at the dash is rendered inoperable, inspect the single 14-gauge blue wire at the sending unit, which is located at the back of the transmission tail housing. That wire runs to the front of the RV. Alternatively, check for a bad ground at the gauge cluster.

Over time hydraulic components have evolved into more sophisticated systems with increased pressure necessitating tighter clearance in the valves and other moving parts of the hydraulic system. Surfaces can be damaged when abrasive particles enter these small spaces. Increased clearance will reduce the effectiveness of the system. For this reason, clean transmission fluid is essential to insure continued operation of the system and reliability of hydraulic circuits.

Filters in the transmission are used as a safeguard to prevent contaminates from entering the system. Proper operation of the transmission system relies upon strict adherence to the recommended maintenance schedule. The MH 3000 and MH 4000 employ two separate filters designated the main filter and the lube filter. Change the main filter at the first 5,000 miles. The hydraulic filter used for power steering and cooling fans is a HC 5710, Silicone Impregnated Cellulose Filter with a 10-Micron rating. Keep record of all filter changes and retain the receipts.

Lubrication of gaskets during filter change may be necessary depending on the individual transmission. Refer to your Allison operations manual for detailed instructions on lubing filter gaskets.

What is the difference between TranSynd and Dexron III? TranSynd is synthetic oil, clear in color. Dexron III is regular transmission oil that is red in color. After extensive testing, TranSynd has proven to improve shifting quality and cooler characteristics, thereby extending the life of the RV transmission. TranSynd costs more than Dexron III. Do not mix Dexron III with TranSynd. When changing brands of transmission fluid within the system, keep in mind that change intervals will also require modification.

Check fluid levels when the RV is on level ground and the engine is running at operating temperature. Fluid changes can be affected by traveling in extreme heat, or while towing large loads up steep grades. All oils are designed to break down over time, however, excess heat will accelerate and cause the oil to discolor and burn. When traveling in mountainous regions, through hot climates, or while pulling large loads, increase transmission fluid and filter changes. Relying on the use of oil analysis to extend oil changes may not be cost effective when taking into consideration the cost of having the oil tested, length of time to receive results, and overall reliability. Designed for use in the transport trucking industry, oil analysis is often needless expense for the RV'er that diligently follows maintenance schedules. For further information on customizing your individual filter and fluid change schedules, contact a certified Allison technician.

Use caution when adding fluid to the hydraulic reservoir. Employing a contaminated funnel to add the fluid can cause problems down the road. Lint detaching from shop rags can cause the hydraulic pistons to stick in the open position and create a loss of necessary pressure. Prior to replenishing transmission fluid, insure that all tools, as well as the surrounding work areas, are free of debris.

Too much fluid can cause the lubricant to bubble and overheat. Instead of lubricating the transmission components, fluid gets thrown around and causes the transmission to fill with oily air pockets. Too little fluid can cause erratic shifting from not having enough oil to do the job. Carefully monitor fluid levels using the transmission dipstick, or on some model coaches, through the transmission shifter at the dash. Prior to starting off every drive day, carefully inspect the ground around the vehicle for signs of oil leak.

In the event that the system experiences a failed hose to the hydraulic fans or power steering while you are away from home, seek assistance from a service source knowledgeable in hydraulics. A new hose will need to be flushed prior to installation. Fluid added to the hydraulic tank must be clear of contamination.