The Final Drive Centre
The Total Solution for Excavator Final Drives

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01473 827145

ATTENTION Case drain — Leak-off.
All piston type hydraulic motors leak oil from the barrel and piston assembly (sometimes called the rotating group assembly) into the motor casing. This leakage is deliberate and lubricates the piston slippers and swash plate (or thrust plate) as well as the interface between the valve plate (or lens plate) and the cylinder block. The oil that leaks into the motor casing has to find it’s way back to the tank under very little pressure and a leak-off pipe (or drain line) runs from the travel motor to the hydraulic tank for that purpose. If the leak-off pipe is not connected or becomes blocked or pressurised, oil pressure will build up in the motor casing and can, and usually does, cause catastrophic damage to the travel motor and often the final drive gearbox. It is therefore vital to ensure that the leak-off pipe is connected correctly, is not obstructed and has no significant back pressure.

• Flow and Return. The flow and return ports are often marked A / B on the hydraulic manifold and are usually the two biggest ports on the travel motor. Where there are four ports in a row the flow and return will almost always be the two centre ports.
• Case drain. On modern final drives with an integrated gearbox and travel motor it is usual to find two case drain ports, one on either side of the flow and return ports.
• Two speed. This tends to be the smallest port on the travel motor and on final drives with an integrated gearbox and travel motor can be found at the front of the drive between the flow and return ports, or toward the rear of the travel motor pointing at 90^o to the other ports or even at the back of the motor.
• Brake port. With the exception of tracked dumpers and other faster moving tracked machines it is unusual to find a brake port in an integrated gearbox and travel motor as the brake is usually controlled automatically. Where a separate “plug-in” motor is used the brake port is usually found on the gearbox.

1. 3 Ton mini excavator final drive with integrated 2 speed travel motor showing 5 front entry ports. The case drain ports are interconnected and either can be used.
2. 1.5 Ton mini excavator final drive with single speed orbital type travel motor showing 2 entry ports. Note there is no need for a case drain port on this motor.
3. 12 Ton excavator final drive with “plug in” 2 speed travel motor. Note that there is another case drain port out of view opposite the port shown, either can be used.
4. 3.5 Ton mini excavator final drive with integrated 2 speed travel motor showing 4 front entry ports and with the two speed port to the side. The case drain ports are interconnected and either can be used