Forward clutch - power shuttle GBA20 gearbox


Removing and install the forward clutch


Disconnect the tractor between the engine and the gearbox.
Drain the gearbox and the centre housing.
Remove the spacer (4) from the gearbox.
Remove the pipes (86) and (87). Detach and remove the cover plates (37) and (83), the flange (80) and the pipe (78).


Remove the pipes (31) (74) (76) (94).
Remove the forward clutch (2) and release it from the housing using a makeshift tool.
Clean the components. Replace those that are defective. If forward clutch shimming is necessary.
Check that the PTO shaft (1) is installed.
Install the clutch using the tool used for removal.


Replace the seals (67) and (75). Install the pipes (31) (74) (76) (94). Replace the "O" rings (95).

Clean the mating faces on the gearbox housing and the cover plate (37). Smear the mating face of the housing with Loctite 510 or equivalent.
Replace the dust seal (96) and the "O" ring (81).
Install the pipe (78), the flange (80) and the cover plates (37) and (83) smeared first with Loctite 510 or equivalent. Tighten the screws to a torque of 84 - 110 Nm.
Tighten screw (97) moderately and screws (79) to a torque of 44 - 53 Nm.
Reconnect the pipes (86) (87).
Install the gearbox spacer (4).
Top up the oil level in the housings. Check it using the gauge at the rear of the centre housing.
Reconnect the tractor between the engine and the gearbox.
Carry out a road test of the Power Shuttle and high and low Speedshift ranges.
Check the tightness of the mating faces on the spacer (4), the cover plates (37) and (83) and the hydraulic unions.

Disassembling and reassembling the forward clutch

Separate the bell (33) from the unit (18). Remove the discs (29) and the intermediate plates (30).
Remove the front snap ring (9). Remove the splined ring (6), the anti-extrusion rings (8) and seal (7).


Remove the circlip (11). Remove the cover plate (2) from the pump (14) complete with bearing (12).
Take the lubrication pump out of the fixed unit (1) and separate it from the clutch unit (18).
Remove the rings (15). If necessary, extract ring (16) and remove the 1.5 bar valve (73).
Place the partially disassembled clutch on a suitable makeshift fixture.
Compress the Belleville washers (25) and remove the rear snap ring (9).
Remove locking ring (5). Gradually de-compress the Belleville washers.
Separate the clutch housing (18) fitted with the piston (28) from the shaft (19).
Remove the Belleville washers and the ring (100).
Remove the snap ring (23). Take out the shaft (19) complete with bearing (22) from the hub (27).
Remove the circlip (21). Extract the bearing (22) from the shaft (19).
Remove the piston. Remove the seals (24) (69). Discard them. If necessary, extract the bearing (68) from the unit (1) of the pump (14).
If necessary, remove snap ring (54) and remove the input sun gear (53). Remove the snap ring (65).
Extract the bearing (32).
Make sure that the pin (20) is fitted.
If removed, fit the bearing (32) on the bell (33), using a press and a suitable fixture. Install the snap ring (65).
If removed, fit the bearing (68).

Lubricate the new seals (24) (69) and fit them on the piston.
Install the piston (28), using a pin of suitable diameter to align the index holes bored in the unit (18) and piston. The angular position of the piston depends on the position of the lubricating ports for the unit (18). Complete the installation of the piston by gradually and alternately striking its rim with a plastic hammer. Check that there are no seal fragments after fitting.
Using a suitable fixture, force fit the bearing (22) on the shaft (19), with the sealed side directed towards the reverse clutch. Install the circlip (21).
Install the assembly (shaft, bearing, circlip) in the hub (27). Install the snap ring (23).
Install the ring (100) and the Belleville washers.
Assemble the unit (18) fitted with the piston (28) on the shaft (19).
Compress the Belleville washers using the same fixture. Position the ring (5), aligning two of the flat sections with those of the unit (18). Replace the rear snap ring (9) and correctly position it in the bottom of the groove.
Remove the fixture.
Check that the rings (15) turn freely in their grooves. Position the rings, lightly smeared with miscible grease, making sure that they do not protrude beyond the rim of the unit (18).
If required, fit the 1.5 bar valve (73). Tighten to a torque of 47 - 54 Nm. Insert ring (16) using a suitable fixture, with the chamfer "C" turned.


Lubricate the ring. Assemble fixed unit (1) on the unit (18).
Lubricate pump (14) with transmission oil and position it aligning the flat sections of the rotor with those on the unit (18).
Manually check the angular movement of the rotor on the flat sections of unit (18).
Install the bearing (12) on the cover plate (2) of the pump. Install the cover plate. Install the circlip (11) and screws (13) and tighten to a torque of 25 - 35 Nm.

Lubricate and fit a new assembly ("O" ring (7) and anti-extrusion rings (8)). Slide on the splined ring (6). Install a new front snap ring (9).
Soak the discs (29) in a transmission oil bath for approximately 1 hour. Check that they are correctly
impregnated.


Position the intermediate plates (30), by aligning their lugs and the discs (29) on the hub (27). The number of discs and intermediate plates depends on the tractor type. The bell (33) differs according to the number of discs.
Position the bell (33) onto the unit (18) with Loctite 549 or equivalent, with the lugs of the intermediate plates inserted in the slots of the bell. Fit and tighten the screws (66) to a torque of 25.5 - 34.5 Nm.
Manually check the rotation of the hub (27).
If necessary, Install the input sun gear (53) and position the snap ring (54).

Shimming the forward clutch


This operation involves obtaining an axial clearance J1 of 0.60 to 0.80 mm between the pump cover plate (2) and the spacer (4). To carry out this operation, remove the PTO shaft.
Install the clutch to the cover plate (38) of the reverse clutch.
Install an approx. 2 mm thick shim (3) onto the cover plate (2).

Lubricate the lip of the seal (10). Protect the lip of the seal by fitting a guard on the splines of the shaft (19). Install two guide studs on diametrically opposed sides of the gearbox housing and temporarily refit the spacer (4) without Loctite. Gradually tighten several screws.

Place a dial gauge at the end of the shaft (19) and check the clearance by moving the shaft sideways. Check that the snap ring (65) for the bearing (32) is correctly in contact with the cover plate (38).

Remove the spacer (4). Depending on the reading previously obtained with the dial gauge, define a new thickness of shim(s) (3) in order to obtain a J1 clearance between 0.60 and 0.80 mm.