Front Axle - 4WD GPA20 clutch

The front axle clutch assembly is fitted in the lower part of the rear axle housing. An inspection cover
located under the housing provides access to the mechanism, which comprises:
- a shaft (25) turning on two tapered roller bearings fitted in the bore of the axle housing,
- a hydraulic clutch assembly attached to the rotating shaft
- a bell gear (15) centred on the shaft by a ring (43), driving the clutch discs (36).
The helical bell gear (15) is constantly meshed to the gear (7) on the pinion.
The shaft is shimmed to obtain an operating clearance between 0 and 0.10 mm using shims (20) positioned between the cap (22) and the cup (18).


The 4WD solenoid valve sends the 17 bar pressure into the shaft (25) via a channel drilled in the axle housing and the ring (11). The cover plate (30) moves on the hub (40) and pulls the bell (42) which compresses the Belleville washers (34) and (35), releasing the discs (36). The bell gear (15)
attached to the ring (43) turns idle on the shaft.

The pressure drop releases the Belleville washers, which push the bell (42) so that it becomes attached to the bell gear (15), which in turn drives the shaft (25). The oil then returns to the housing via the solenoid valve.

Parts list
(1) Sleeve (2) Double pin (3) Shaft (4) Double pin (5) Sleeve (6) Circlip (7) Gear (8) Plug (9) Needle roller bearing (10) Screw (11) Ring (12) Seal rings (13) Cup (14) Cone (15) Bell gear (16) Clutch assembly (17) Cover plate (18) Cup (19) Cone (20) Shim(s) (21) "O" ring (22) Cap (23) Circlip (24) Seal (25) 4WD drive shaft (26) Seal (27) Stop screw (28) Flange (29) "O" ring
(30) Cover plate (31) Circlip (32) "O" ring (33) "O" ring (34) Belleville washer (35) Belleville washer
(36) Disc
- A. 4-disc clutch
- B. 5-disc clutch
(37) Thrust plate
- A. 4-disc clutch
- B. 5-disc clutch
(38) Cover plate (39) Circlip (40) Hub (41) Shim(s) (42) Bell (43) Ring

Removing the clutch assembly

Chock the tractor. Drain the rear axle housing.
Disconnect the two front differential lock control hoses (plug the channels). Remove the guard and the transmission shaft. Remove the engine clutch or Power Shuttle lubrication pipe that is fitted to the lower cover plates of the centre housing and the gearbox.
Remove the screws (10) and the cover plate (17). On tractors fitted with proportional PTO, recover the spring (3), the detent plunger (2) and the retainer pipe (1). On tractors fitted with a reinforced sealed guard, remove the screw (27), flange (28) and seal (26).

Remove the circlip (23).
Protect the splined part of the shaft (25). Extract the cap (22) with its seal (24) using the makeshift tool. Remove the seal (24).

Remove the "O" ring (21).
Remove the shims (20) and the cup (18). On tractors fitted with proportional PTO, place the control in declutched position.
Extract the shaft assembly (25) and bearing cone (19), while holding the clutch assembly (16) and the bell gear (15).
Remove the clutch assembly (16) with the bell gear (15) and the cone (14).

Using a makeshift tool, extract the ring (11). This tool is essential for tractors with proportional PTO. If necessary, also remove the cup (13) using a suitable extractor. When removing the gear (7), it is necessary to remove the right-hand hydraulic cover plate.

Tractors with no creeper unit
Drive out the double pins (2) (4) from the coupling sleeves (1) (5).
Slide the sleeves towards each other on the shaft (3) and remove the shaft - sleeve assembly.
Take off the circlip (6) and remove the gear (7).

Tractors with a creeper unit
Take off the circlip (6) and remove the gear (7).

Disassembling the clutch

Detach the bell gear (15) from the clutch assembly (16).
Remove the circlip (31).
Remove the cover plate (30).
Remove the "O" rings (29) (32).
Using a press and a suitable fixture, compress the Belleville washers (34) (35).

Take off the circlip (39) and the shim(s) (41).
Remove the suitable fixture.
Remove the cover plate (38), the discs (36) and the thrust plates (37).
Separate the hub (40) from the bell (42).
Remove the "O" ring (33).
Remove the Belleville washers (34) (35).

Disassembling the shaft
Remove the two rings (12).
Extract the cone (19) using a press and a suitable fixture.
Extract the needle roller bearing (9). Remove the plug (8).

Reassembling the shaft

Check that the shaft channel is not blocked.
Tighten the plug (8) smeared with Loctite 542 to a torque of 10 Nm.
Install the needle roller bearing (9) 2.5 mm set back from face F.
Install the bearing cone (19) against the shoulder of the shaft (25).

Reassembling the clutch

Check and clean the components and replace those that are defective. Check that the 17 bar channel in the hub (40) is not blocked.

Position the Belleville washers (35) (34) in the bell (42). Two types of Belleville washers with different markings and different loading efforts can be fitted:
- 3619147M1 marked 147
- 3619473M1 marked 473.
The clutch assembly is normal or reinforced depending on the tractor types.
Lubricate and fit the "O" ring (33) on the hub (40).
Place the hub (40) in the bell (42), braced against the Belleville washers.
Install the discs (36), aligning the lugs and the thrust plates (37), and fit the cover plate (38).

Adjusting J1 clearance 

Using a press and suitable fixture apply a load of 2000 daN to fully compress the Belleville washers (35) (34). Install the circlip (39). Use a set of shims to increase the distance X between the cover plate (38) and the circlip (39). Select the shim(s) (41) to obtain a clearance J1 = 0.9 to 1.1 mm.
Remove the circlip (39).
Position the shim(s) chosen between the cover plate and the circlip (splined shim on the circlip side).
Reinstall the circlip.
Lubricate and fit the "O" rings (32) (29) on the cover plate (30) and refit the cover plate.
Install the circlip (31).
Install the clutch assembly (16) on the bell gear (15). The ring (43) is force fitted in the bell gear (15) and then rebored.

Install the clutch assembly

Tractors with no creeper unit
Reinstall the gear (7) (if removed).
Position the circlip (6).
Reinstall the connecting shaft and coupling sleeves. Replace the double pins.

Tractors with a creeper unit
Reinstall the gear (7) (if removed).
Position the circlip (6).
Reinstall the right-hand hydraulic cover plate.
Install the cup (13) (if removed).
Install the ring (11) using a makeshift drift, so that the ring is positioned 4 to 5 mm set back from the cup mating face (13). Move the ring until one of its holes opens into the clutch supply
channel in the housing.

Install the seal (24) in the cap (22).
In order to correctly "seat" the cones in their bearing cups, to obtain the clearance: J2 = 0 to 0.10 mm, fit the cone (14), the shaft (25), and the cup (18).
Protect the splines of the shaft.
Install the bearing (22) and the circlip (23)
Place the dial gauge feeler pin against the end of the shaft (25).

Pull the shaft, while turning it alternately from right to left to correctly seat the cones in the cups.
Set the dial gauge to zero.
Depending on the clearance measured, select the thickness of the shim(s) (20) required to obtain J2.
Remove the circlip (23), cap (22), cup (18) and the shaft (25).
Install the seal rings (12) in the grooves of the shaft (25) and hook their ends. Ensure that they turn freely.

Install the cone (14) into the cup (13). Insert the shaft (25) after having positioned the clutch assembly (16) and bell gear (15) in the housing.
Install the cup (18) and the shim(s) (20) (smeared with grease).
Install the "O" ring (21) in the housing groove.
Install the cap (22) and the circlip (23), and remove the spline protection on the shaft.
On tractors with reinforced sealing, grease and position the seal (26), with the lip turned towards the cap (22). Remove the safety shield.
Install the flange (28), ensuring that operational clearance remains between the flange and housing.
Tighten the screw (27) after smearing it with Loctite 241.
Clean and degrease the mating face of the cover plate (17) and the housing.
Smear the mating face of the cover plate with a sealing product (Loctite 510 or equivalent).
Screw two opposing guide studs into the housing.

On tractors fitted with proportional PTO, check the position of the lever (4). Fit the retainer pipe (1), the detent plunger (2) and the spring (3).
Put the cover plate back on (17).
Remove the guide studs, and fit and tighten the screws (10) to a torque of 130 - 170 Nm.
Smear the two sleeves of the 4WD transmission shaft with "Anti Seize" grease or equivalent. Refit the transmission shaft and guard, and reconnect the two front differential lock hoses. Refit the lubrication pipe for the Power Shuttle or engine clutch.
Top up the rear axle oil level and remove the shims.
Check clutch operation and proportional PTO control adjustment (if fitted).
Check tightness of:
- the mating faces of the cover plate under the rear axle housing
- the right-hand hydraulic cover plate (if removed)
- Hydraulic unions