John Deere – 1023E, 1025R and 1026R – Steering System Operation

The hydraulic pump above the rear PTO shaft supplies hydraulic pressure to the PTO solenoid valve. The solenoid valve has a pressure relief valve that opens at a minimum pressure of 2068 kPa (300 psi). The PTO valve contains a divider valve that sends 50% of the oil to the loader selective control valve (SCV), and 50% to the steering control valve (SCU).

The SCU utilizes an open center control valve to operate the steering cylinder. When the steering wheel is turned, the SCU directs hydraulic pressure to the appropriate steering cylinder hose. The pressure pushes the cylinder ram, which pivots the front spindles and wheels. The SCU contains a 75 bar (1087 psi) relief valve.

The SCU and steering cylinder cannot be rebuilt, and must be replaced as complete units.

Excess oil from the SCU is sent to the oil cooler, mounted in the front of the machine. After the oil is cooled, it passes through an in-line filter and goes to the hydrostatic transmission.
The hydrostatic transmission is a combination motor and pump, and operates as a closed loop. Most of the hydraulic oil delivered to this unit passes through the charge pressure relief valve and returns to the reservoir.

A small amount of oil flows through the hydrostatic unit, providing makeup oil and internal
lubrication, and then returns to the reservoir.