Robotic mechanical GBA25 gearbox - Removing and install the primary and secondary shafts


Drain the transmission oil. Split the tractor in order to remove only the robotic gearbox (if servicing only concerns the robotic gearbox) or the complete Dyna-4 unit (then split the two housings). Remove:
- all hydraulic pipes fitted to the unit housing
- the PTO shaft.


Removing the primary and secondary shafts
Rig up four makeshift legs on which to set the unit vertically. Use an 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.
Position the unit on the legs, with the cover (6) on top.


Take off the covers (102) and (111). Unscrew the castellated nuts (99)(101) and (108)(109)Retighten the safety finger rod (106) to its maximum.
Remove the two plugs (126) and (127)Drive out the two pins (97) and (125) holding the forks on the selector rails. The pins will fall into the gearbox housing. They must be recovered when the gearbox is disassembled.
Remove the circlip at the rear of the gearbox (84).
Using a plastic hammer, remove the selector rail (98) towards the rear of the gearbox. The rail control piston assembly is fitted to the rail and is removed with it. Part of the sleeve remains in the cylinder. If it must be removed, take off the circlip (87) and extract the sleeve. Remove the screws (A) from the cover (6).


Install two screws (B) in the threaded holes in order to lift up the cover (6).
Remove the cover (6). Recover the bearing cups (3), (8) and (114) and the shims (4), (7) and (113). Recover the lubricating pipe (12), the seal (10) and the spring (11)Remove the circlip (82).
Using a plastic hammer, remove the selector rail (73) towards the front of the gearbox. The rail control piston assembly is fitted to the rail and is removed with it. Part of the sleeve remains in the cylinder. If it must be removed, take off the circlip (76) and extract the sleeve.

Disassembling and reassembling the selector rail (98) (ranges 1 and 2)


Clamp the rail (98) in a vice equipped with protective jaws.
Tighten the two pistons (92) in the vice to compress the spring.
Remove a snap ring (91). Remove the pistons (92) and the spring (93).
Replace the seals (129) on the rail (98).
Carry out operations in reverse order to assemble the selector rail.
Turn the forks (72) and (96) inwards in the gearbox to allow them to enter the housing.
Place service tool ref. 3378804M1 in the primary and secondary shafts.
Sling the tool using a pulley hoist or a suitable lifting system. Extract the two shafts (1) and (13) from the gearbox housing. Take care when the 1st/2nd gear synchronizer is passing beside the reverse shaft support. The total weight of the two shafts is approximately 44 kg (lower shaft line = 27 kg, upper shaft line = 17 kg).
Remove the assembly and place it on a workbench. Remove the service tool and split the two shafts. If required, extract the bearing cups (47), (51) and (118) from the gearbox housing. If necessary, remove deflector (52).

Reinstall the primary and secondary shafts
Ensure all parts are clean and in good condition. Check that the lubricating ports and range control ports are clean.
Replace all the "O" rings, greasing them lightly before assembly. Do not forget to replace the "O" rings (74), (75), (78), (90), (94) and (95) in the selector rail bores inside the housing. Check the presence of the bearing cups (47), (51) and (118) in the housing (5).
Assemble the shafts (1) and (13); Place service tool ref. 3378804M1.
Install the forks (72) and (96) on the synchronizer sliders. The offset side of the fork must be turned towards the front of the tractor. The two forks are identical. They have the same reference.
Install the two shafts in the housing. At the same time, Install the reverse transfer pinion (116) fitted with the two bearing cones (115) and (117). Ensure the pinion (116) is positioned correctly. The marks on the teeth should be turned towards the bottom of the housing.
Reinstall the lubricating pipe (12) fitted with a new "O" ring (10) and the spring (11).
If the sleeve (77) and the circlip (76) have been removed, grease the sleeve, insert it into the cylinder, then fit the circlip (77).
Thread the selector rail (73) with the lightly greased piston assembly into its housing. To help insert the selector rail into the fork, use a pin punch to hold the fork in place. Install the plug (80) fitted with two new "O" rings (81) (83). Install the circlip (82).
If the sleeve (88) and circlip (87) have been removed, grease the sleeve, insert it into the cylinder, then fit the circlip (87).
Thread the selector rail (98) with the lightly greased piston assembly into its housing. To help insert the selector rail into the fork, use a pin punch to hold the fork in place. Mount the plug (85) fitted with two new "O" rings (86) (128). Install the circlip (84)Align the holes in the forks (72) and (96) with those in the corresponding selector rails.
Insert new pins to attach the forks to the selector rails. Install the plugs (126) and (127).
Check the interlock mechanism is in position and retighten the rods (104) and (106) to their maximum tightness.
Install the four switch thrust pins (130) using a bit of grease to hold them in positionIn the cover (6), Install the bearing cones (3), (8) and (114) smeared with grease to hold them in position. Also Install:
- the original thickness of shims if the roller bearings have not been replaced
- the calculated thickness of shims if the roller bearings have been replaced.
Put the cover back on (6). Install the cover (6) screws smeared with Loctite 242. Tighten to a torque of 57–77 Nm.
Reinstall the ring (52) with the lubricating port turned towards the top of the gearbox. Fix it in position with four punchmarks.
Adjust the selector rails and forks. Adjust the interlock mechanism.