GBA25 gearbox - Remove and install the Power Shuttle

Drain the transmission oil Split the tractor between the engine and the gearbox. Remove:
- either the complete gearbox (if an operation is to be carried out on the whole transmission assembly)
- or only the Powershift module from the unit by leaving the mechanical unit coupled to the rear axle (if servicing is to be carried out on the Powershift module or reverse shuttle only). It is possible to carry out an operation on the forward clutch by splitting the tractor between the Powershift module and the mechanical gearbox.

- all hydraulic pipes fitted to the unit housing
- the unit control hydraulic unit with its connecting pipes
- the union and lubricating pipe of the Powershift module
- the PTO shaft.

If the entire gearbox has been removed, separate the Powershift module from the mechanical gearbox.
Locally make four legs on which to set the unit vertically. Use a M14 screw or threaded rod, and weld on a nut to ensure a minimum distance of 120 mm between the unit and the work surface.
Unscrew the two diametrically opposed screws (A) and replace them with two shackles to sling the gearbox.
Unscrew the 8 screws (B)do not remove screws (C). They hold the front epicyclic gear train housing (D) in place.

Sling the gearbox Powershift module using the shackles.
Make a mark (R) on the housings in order to refit the modules correctly at reassembly.
Install the Powershift module on a fixture positioned on the forward clutch.

Take out the screws holding the cover (26) on the housing (D).
Using the sling, raise and separate the front section of the Powershift moduleDuring this step, the brake, clutch and rear planet-carrier remain on the Power Shuttle. Remove the planet-carrier.
Take out the brake and clutch assembly (G) and the friction washer (H).
Remove the screws from the cover (26) on the bearing (57).

Install the Power Shuttle on a fixture positioned on the forward clutch.
Install the cover (26) on the bearing (57). Ensure there is a snap ring (2) on the shaft (1). Install the cover screws (26) smeared with Loctite 242 or equivalent. Tighten to a torque of 29–37 Nm.
Install the friction washer (H) smeared with oil on the clutch unit (G).
Install the brake and clutch assembly (G) on the coverIf the brake discs and clutch discs have been replaced, they must be soaked for approximately one hour in a transmission oil bath. See the Powershift module chapter for the procedure. Reinstall the planet-carrier (F).
Align the lubricating port (arrow) with a tooth on each planet gear.

Sling the Powershift module.
Check for the presence of return springs (S) in the cover (26).
Aligning the two parts using the mark (R)Take care when inserting the planetary gears into the Powershift module piston.
Install the cover screws (26) to the Powershift module, after smearing them with Loctite 242 or equivalent. Tighten the screws to a torque of 66 Nm.
Clean the mating faces then apply Loctite 510 or equivalent sealing product.

Reinstall the "O" ring. Smear it with grease and Install it on the Powershift module. Sling the reverse shuttle and Powershift module assembly. Install the assembly in the unit housing. Lower the sling by aligning the centring pin (L) with the portInstall the screws (B) of the housing (D).

Removing and install the Power Shuttle

Reverse clutch
Remove the Power Shuttle assembly. Remove the plate (59). Remove the snap ring (2). Remove the circlip (29).

Remove the bearing (57), reverse pinion (6), bearings (5) (7) and bearing (3) assembly.
If it is necessary to replace the bearings (5) (7), take off the circlip (8), oil deflector (24) and snap ring (25). Mark the order of assembly of the oil deflector (24). Remove the clutch discs (11) and thrust plates (12).
Remove and discard the ringsInstall the reverse shuttle unit on a press with the Belleville washers facing upwards.

Using the tool, compress the Belleville washers (31).
Remove the snap ring (9) and washer (10). Release the press and take off the Belleville washers (31) and thrust washer (13).

Drive off the piston (32) using compressed air. Discard the seals with square sections (33) (34).

Forward clutch
Turn over the clutch unit (14). Remove the circlip (18).
Take off the cover plate (40) with the hub (20) and snap ring (19).
Remove the discs (16) and thrust plates (15).
Repeat steps with the Belleville washers (17), snap ring (44) and washers (45) and (37). Drive out the piston (30) using a jet of compressed air. Discard the seals with square sections (35) (36).

Take off the sealing ring (42) and the bearing (39). Discard the "O" ring (41) and ring (43)If necessary, take off the needle bearing.
"O" rings and seals with a square section must previously be greased to ensure they are positioned correctly. New discs must always be soaked for approximately one hour in transmission oil.
Check the condition of the parts of the mechanism. Replace those that are defective. Ensure the clutch lubricating and control ports in the shaft (1) are clean.

Assembling pistons (30) and (32)
Install new greased seals with square sections (33)(34) and (35)(36) in the grooves of the pistons (30) and (32). Ensure the seals are correctly positioned in the grooves. Grease the piston sleeves in the unit.

Install the pistons (30) and (32) in the unit (14) by striking the rim of each piston alternately with a plastic hammer.

Reverse clutch
Position the washer (13) then the Belleville washers (31) on the unit (14). Using a press and implement, compress the Belleville washers (31).
Install the thrust washer (10). Install a new snap ring (9). Ensure the washer (10) is positioned correctly. Its shoulder should be facing the snap ring.
Grease three new rings (4) and Install them on the grooves of the shaft (1).
If the bearings (5) and (7) have been removed, reinstall them in correct order on the hub (6):
- the bearing (7)
- the oil deflector (24)
- a new snap ring (25)
- the bearing (5).
Ensure the clutch lubricating and control ports in the bearing (57) are clean.
Assemble the sprocket hub (6) with the bearing (57). Install the circlip (8).

Position the bearing (57), sprocket hub (6) and bearings (5) (7) assembly on a fixture with a central hole to insert the shaft (1), with the hub turned upwardsSlide the discs (11) and thrust plates (12) onto the reverse pinion (6). Ensure the discs and thrust plates are stacked in the correct order.
Align the splines of the thrust plates (12).
Lower the reverse shuttle unit (14) so its splines slide onto those of the thrust platesInstall the circlip (29) in the groove on the unit (14).

Forward clutch
If the needle bearing (60) supporting the PTO shaft has been removed, replace it with a new one.
Grease the "O" ring (41) and ring (43). Install them on the sealing ring (42).
On the shaft (1):
- insert the bearing (39)
- insert the ring (42).
Ensure the sealing ring (42) is positioned correctly. Its shoulder (arrow) should be facing the bearing (39).

Carry out steps with the forward clutch. Install the hub (20) in the unit (14).
Slide on the discs (16) and thrust plates (15). Ensure the discs and thrust plates are stacked in the correct order.
Install the cover plate (40) with the snap ring (19). Install the circlip (18).
Reinstall the Power Shuttle assembly.
Install the PTO shaft in the transmission upper shaft line.
Reinstall the hydraulic control covers, and reconnect the hydraulic pipes and hoses.
Assemble the transmission on the engine side and rear axle side, applying Loctite 5206 or equivalent sealant to the mating faces.
Top up the transmission oil level. Carry out a clutch calibration.
Carry out a road test of the gearbox operation. Check that the hydraulics are functioning correctly and check for leaks.