Specifications, Service and Repair of Farm and Lawn Tractors

Massey Ferguson 8480, 8460 Tractor Steering System


The steering system used on Massey Ferguson 8480, 8460, 8470, 8450 Tractors fitted with a DYNA VT transmission and closed centre hydraulics is dynamic, and there is no mechanical link between the steering wheel and the steering ram. Its control principle is of the "Load Sensing" type.

The system comprises the following main components:

- a pressurised oil supply, from a fixed displacement pump via a priority valve,

- an Orbitrol steering unit: OSPDF 80/240 LS Dynamic 4WD with closed centre, by-pass mounted on tractors fitted with a 4WD Dana AG210 or AG280 front axle.

- a double acting steering ram fitted to the 4WD front axle.

The Orbitrol is supplied by a fixed flow rate pump via a priority block. The priority block is controlled by the steering unit Load Sensing line, and directs priority oil flow to the steering circuit; excess flow is redirected to the distribution block then to the cooling circuit.

When MF 8480, 8460, 8470, 8450 Tractor steering remains in neutral, all pump flow is directed to the cooling system. When the steering wheel is turned, the necessary flow of oil is directed to the corresponding side of the steering ram. The other side of the ram is connected to the tank return ports.

In case of engine breakdown or fixed displacement pump failure, the Orbitrol acts as a hand-operated pump so that the steering can be controlled. This obviously requires a much greater effort to be applied to the steering wheel.

The Orbitrol OSPDF 80/240 comprises twin stator rotors of different capacities.

Specifications:

- Shock valves setting: 225 -245 bar
- Supply valve setting: 155 -160 bar
- Steering unit capacity: 240 cm3 / turn
- Steering unit capacity: 80 cm3 / turn
- Supply valve setting: 10 bar
- Return to neutral springs torque: 1.5 daNm

Disassembly and assembly the Orbitrol steering 80/240cm3



Fig.41. Parts list

(1) Lip seal (2) Centring springs (3) Bush (4) O’ring (5) Cotter pin (6) Sleeve (7) Spool valve (8) O’ring (9) Link shaft (10) O’ring (11) Plate (12) O’ring (13) Plate (14) O’ring (15) Spacer (16) O’ring (17) O’ring (18) Integrated spool (19) Spool body (20) Seals (21) O’ring (22) Washer (23) Needle bearing (24) Washer (25) Relief valve (26) Orbitrol steering unit (27) Rotor (gear type 80 cm3) (28) Stator (gear type 80 cm3) (29) O’ring (30) Stator (gear type 205 cm3 or 240 cm3) (31) Rotor (gear type 205 cm3 or 240 cm3) (32) Plate (33) Spring (34) O’ring (35) Closing plate (36) Screw (37) Shock valves (38) Non-return valve (39) Spacers (40) Non-return valve (41) Suction valve (42) Cotter pin

- Remove the steering unit from the tractor.

- Place the Massey Ferguson 8460, 8470, 8480, 8450 Tractor steering unit in a vice fitted with plastic jaws.

- Mark the location of the screws (36) and remove them. Remove seals (20).

- Take off the closing plate (35), the O'ring (34), the body (19), the integrated spool (18) and spring (33).

- Remove the O'ring (17). Locate the position of plate (32) and remove it.

- Remove the O'ring (16). Remove stator (30) and rotor (31). Remove the O'ring (14). Locate the position of plate (13) and remove it.

- Remove spacer (15), stator (28), rotor (27). Locate the position of plate (11) and remove it. Remove the O'ring (10).

- Take out the splined link shaft (9).

- Unscrew the threaded bush and recover the ball from the non-return valve (38).

- Take out the two axle pins and the balls from the suction valves (41) of the steering unit.

- Extract the sleeve (6) and spool valve (7) assembly by pushing it out while checking that the pin (5) lies along the horizontal axis.

- Remove the washers (22) (24), the needle bearing (23) and the bush (3) from the sleeve and spool valve assembly. Remove the pin (5), and the centring springs (2) by pressing on their ends. Separate the sleeve (6) from the spool valve (7).

- Unscrew the plug from the relief valve (25). Using an 8 mm Allen wrench, disassemble the threaded bush and remove the seal, the spring and the valve (the crimped seat cannot be removed).

- Unscrew the two plugs from the shock valves (37) and remove the seals. Using a 6 mm Allen wrench, remove the threaded bushes and take out the springs, the valve balls and their seats (the crimped seats cannot be removed).

- Extract the seal (1) and O'ring (21). Disassemble the non-return valve (40).

- Check and clean all components. Replace any defective parts. Lubricate the components with clean transmission oil.

- Reassemble the non-return valve (40). Install the seal (1) and O'ring (21).

- Place the valve balls and springs in the recesses of the shock valve (37). Screw in the threaded bushes, fit the seals and tighten the plugs.

- Install the valve and spring in the recesses of the relief-valve (25), screw in the threaded bush. Fit the seal and tighten the plug to a torque of 40 - 60 Nm.

- Insert the spool valve (6) into the sleeve (7). Position the centring springs (2) and insert the pin (5).

- Position the bush (3) on the sleeve and spool valve assembly so that the chamfer facilitates assembly in the steering unit.

- Place the washers (22) (24), the chamfer of washer (24) towards the centring springs (2), by inserting the needle bearing (23) between them.

- Install the sleeve and spool valve assembly in the MF 8480, 8460, 8470, 8450 Tractor steering unit by oscillating it slightly. Check that the pin (5) is held horizontally.

- Install the two valve balls and the two pins in the recesses of the suction valves (41).

- Install the valve ball in the recess of the non-return valve (38) and screw in the threaded bush.

- Position the splined link shaft (9). Install the O'ring (10) and the distributor plate (11).

- Install the rotor (27) so that the two concave depressions C lie along the axis of the slot in the splined link shaft (9).

- Place the O'rings (12)(29) on the stator (28).

- Align the stator (28) fitting holes with those of the spool valve. Refit the stator on the spool valve without moving the rotor (27). The rotor (27) and the pin (5) must be in the correct position.

- Install rotor (31) on the spacer (15) so that the two depressions C lie in the axis of the slot of splined shaft (9).

- Place the O'rings (14)(16) on the stator (30). Fit and move the stator (30) with an angular movement so that the fixing holes align with those provided in the steering unit.

- Install plate (32) in the position marked at disassembly.

- Check that there are no scratches on the bore of the body (19) or on the spool rim (18).

- Check that the spool moves normally in the body.

- Slide the spool fitted with its oil tightness components into the body. Fit O'rings (17) (34) and spring (33). Install the cover plate (35).

- Install the new seals (20) and screws (36) as marked at disassembly. Alternately tighten the screws to a torque of 30 - 35 Nm.

- Using a test-bench or a suitable fixture, check the adjustment and correct operation of the steering unit.

- Install the steering unit on the Massey Ferguson 8480, 8460, 8470, 8450 Tractor. Check the oil tightness of the hydraulic unions.

Manual steering (engine stopped)

When the pump is no longer providing pressure or when the pressure is too low, the rotors (27) (31) are no longer hydraulically driven. It is no longer power assisted. In this case, action on the steering wheel compresses the centring springs (2).

The angular clearance between pin (5) and sleeve (6) is caught up and there is a mechanical driving of the metering device (stator (28) and rotor (27) only). The steering unit then operates in the same way as a hand pump.

The oil returning from MF 8460, 8480, 8470, 8450 Tractor steering ram A passes through the non-return valve (38) and supplies the metering device. The pressure generated is proportional to the torque applied to the steering wheel. A great effort is therefore required to turn the wheel in order to steer the tractor.



Fig.42. Legend

A - Double acting steering ram, BP - Priority block(s), L - LH hydraulic port of the steering ram, LS - Signal, P - Pressure, R - RH hydraulic port of the steering ram, T - Return.

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