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How To Make Hydraulic Connections to a Single Speed Final Drive
Incorrect installation of hydraulic lines can cause terminal failure of your final drive.
This post will help identify the hydraulic connections relevant to a single speed final drive – there may be up to 4 hydraulic connections:
- Two hydraulic lines to power the drive motor. These are the flow and return lines connected to the A & B ports (see images)
- A case drain / leak-off. It is very important to connect this to the correct DR port where applicable – see below
- A brake line. If fitted it is usually connected to the gearbox rather than the travel motor
Below are some examples of single speed final drives with their ports identified.
1.5T Mini Excavator
Single speed orbital type final drive showing 2 entry ports. Note there is no need for a case drain port on this motor.
8T Mini Excavator
Integrated single speed final drive showing 4 front entry ports. The DR ports are interconnected and either can be used.
A & B Ports (Flow and Return)
Forward and reverse main pressure ports. These are commonly the largest ports and are usually close together in the middle of the hydraulic manifold.
DR1 & DR2 Ports (Case Drain)
Drain line / leak off ports. Placed on either side of the A & B ports. Only one is used, always attach the case drain pipe / hose to the upper port and fit a metal plug to the lower port.
Some single speed final drives have a single case drain port between the A & B ports.
All conventional axial piston motors must have a controlled leakage from the rotating group (motor) into the casing. This oil lubricates all moving parts within the rotating group and it MUST be able to drain back to the hydraulic tank relatively unrestricted via the swivel joint and return line filter.
The case drain oil also lubricates both motor shaft bearings. It is important that the case drain hose is connected to the uppermost case drain port (where there is an option) so the drive motor case is constantly full of hydraulic oil.
Brake Port
With the exception of Tracked Dumpers and other faster moving tracked machines it is uncommon, but not unusual, to find a brake port in an integrated gearbox and motor as the brake is usually controlled automatically.
Where a separate “plug-in” drive motor is used the brake port is usually found on the gearbox. If equipped, the port location will be clearly shown in the installation instructions.