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Massey Ferguson 8240, 8250 gearbox - Dynashift with power shuttle

MF 8100-8200 Series Tractors Repair Operations

On Massey Ferguson 8240, 8250 tractors the Dynashift can also be mounted on an input unit fitted with a mechanical reverse shuttle.

This section only describes the Dynashift with power shuttle. The operating principles of the two Dynashift versions are similar.

However, housing profile of the Dynashift with power shuttle is different because of the location of the power shuttle rear clutch and the driving gear located at the rear end of the housing.

MF 8240, 8250 gearbox dynashift is located between the rear clutch and the driving gear of the power.
It is a hydraulically controlled gear shift mechanism and provides the gearbox with four input ratios.
The function is ensured by two epicyclic gear trains associated with two hydraulic clutches.

Dynashift design enables selection of each of the four ratios while driving, and under load, without declutching, using a lever mounted to the left under the steering wheel.

(1) Secondary ring gear carrier (2) Intermediate plates (3) Front clutch discs (4) Belleville washer (5) Splined hub (6) Needle bearing (7) Transmission shaft (8) Ring restrictor (9) Screw (10) Friction washer (11) Bearing (12) Washer (13) Front cover (14) Clutch housing (15) Front brake discs (16) Thrust plate (clutch - brake) (17) Clutch plate (18) Screw (20) Springs (21) Spacer casing (22) Front piston (23) Rivet (24) O’ring (25) Screw (26) O’ring (27) Ball bearing (28) Primary planet carrier (29) Rivets (30) Screw (31) Primary ring gear (33) Screw (34) Secondary ring gear (35) O’ring (36) O’ring (37) Rear piston (38) Clutch plate (39) Secondary planet carrier (40) Cover (41) Rear brake discs (42) Screw (44) Clutch plate (45) Thrust plate (clutch - brake) (46) Screw (47) Cover (48) Intermediate plates (49) Retaining ring (50) Rear clutch discs (51) Friction washer (52) Belleville washers (53) Secondary shaft (54) Splined hub (55) Circlip (56) Spacer (57) Ball bearing (58) Ball bearing (59) Rear clutch housing (60) Retaining ring (61) Secondary sun gear (62) Retaining ring (63) Needles (64) Primary sun gear (65) Springs (69) Circlip (70) Stop (71) Shim(s) (72) Retaining ring (74) Rivets (75) Oil splasher (76) Stud washer (77) Spring washer (78) Washer (79) Locating pin

The Dynashift housing is controlled by two solenoid valves mounted on the clutch unit located on the front right hand side of the gearbox.

The two solenoid valves are controlled by the MF 8240, 8250 tractor’s electronic system.

The Dynashift input unit comprises two epicyclic gear trains: the primary epicyclic gear train is the input unit’s main component and transmits the movement of the engine to the gearbox, the secondary epicyclic gear train controls the speed of the primary sun gear.

Primary epicyclic gear train

The movement comes in via the primary ring gear (31) which is splined onto the transmission shaft (7).

The ring gear turns at the same speed as the engine.

The movement exits via the planet carrier (28) which is splined onto the secondary shaft (53).

The primary sun gear (64) is driven by the secondary epicyclic train.

The speed of this sun gear determines the reduction ratio of the gearbox.

Secondary epicyclic gear train

This epicyclic gear train is controlled by two Massey Ferguson 8250, 8240 hydraulic clutches and brakes.

The secondary ring gear (34) is:

- either locked onto the transmission shaft (7) by the three clutch discs (3) and the Belleville washer (4) located in the front part of the housing,

- or immobilized in relation to the housing by three brake discs (15) and a piston (22).

- When there is no pressure, the piston (22) is pulled back by the twelve springs (20) and the Belleville washer (4) by means of the thrust plate (16).

- When the 17 bar pressure is built up in the circuit, the piston (22) moves forward and blocks the brake discs (15) while pushing the thrust plate (16) that compresses the Belleville washer (4).

Speed of the secondary ring gear is established as follows:

- speed equals engine speed if the front piston is not under pressure.
- speed nil when the front piston is under pressure.

The secondary sun gear (61) is:

- either locked onto the secondary transmission shaft by means of four clutch discs (50) and two Belleville washers (52) located on the rear section of the housing, or immobilized in relation to the housing by means of three brake discs (41) and a piston (37).

- When there is no pressure, the piston (37) is pushed forward by the Belleville washers and the six springs (65).

- The 17 bar pressure moves the piston (37) back and locks the brake discs (41). The piston compresses the Belleville washers (52) by means of the thrust plate (45) that releases the secondary MF 8250, 8240 transmission shaft clutch discs.

- Immobilization of either the secondary ring gear (34) or the secondary sun gear (61) modifies the speed of the secondary planet carrier (39). The latter drives the primary sun gear (64), and this establishes the gearbox reduction ratio.

Explanation of the ratios

Ratio A: Reduction 1/1.620

The two pistons (22) (37) are simultaneously under pressure from the 17 bar circuit.
The secondary ring gear (34) is locked onto the casing by means of the front brake.
The secondary sun gear (61) is locked onto the casing by the rear brake.

Consequently:

- the secondary epicyclic gear train is locked
- the primary sun gear (64) is locked
- the reduction ratio is only set by the primary epicyclic gear train.
- This is standard kinematics, movement comes in via the ring gear and exits via the planet carrier; the sun gear does not move.

Ratio B: Reduction 1/1.386

Front piston (22) is under pressure. Front brake locks the secondary ring gear (34) onto the casing.
Rear piston (37) is not under pressure.

The secondary sun gear (61) rotates with the secondary Massey Ferguson 8240, 8250 transmission shaft (53) (clutch engaged).

The secondary planet carrier (39) is rotating at a low speed, driving the primary sun gear (64).

The rotational speed of the primary planet carrier (28) corresponds to the speed difference between the primary ring gear (31) and the primary sun gear (64). Reduction effect is therefore minor.

Ratio C: Reduction 1/1.1704

Rear piston (37) is under pressure. The rear brake locks the secondary sun gear (61) onto the casing.
The front piston (22) is not under pressure.

The secondary ring gear (34) rotates with the transmission shaft (7) thereby transmitting a higher speed to the secondary planet carrier (39).

The primary sun gear (64) is driven by the secondary planet carrier (39) at a higher speed than in ratio B. Reduction is therefore lower.

Ratio D: Reduction 1/1 ratio

The two pistons are not under pressure. The two clutches are therefore engaged.