GPA40 rear PTO Clutch


Rear PTO clutch engagement and disengagement are controlled electrically by a proportional solenoid valve, which is itself controlled by the tractor's electronic system. The clutch, located at the front and in the upper section of the centre housing, controls the operation of the rear PTO. It is connected in rotation to the engine flywheel via a vibration damper fixed to the flywheel and a line comprising two shafts. It consists of a unit (9) supported by two ball bearings (2) (7) centred in a support (32) fitted to the centre housing. The sleeve (27) supports the ball bearing (22), the drive hub (21) and the piston (10). The clutch housing (9) comprises:
- at the front, a helical gear (28), fixed using screws, which transmits the movement to the hydraulic pumps. For tractors equipped with GTA1540 transmission, gear P1 (28) has spur cut teeth. It is also fixed using screws;
- at the rear, a bell housing (15) with a set of discs (17) and intermediate plates (14). A sealing ring (3) minimises leakage between the rear end of the gearbox upper shaft and the clutch unit (9).

Clutch engaged position
The rear PTO clutch is supplied via the 17 bar (GTA1040 tractor transmission) or 21 bar (tractors equipped with GTA1540 transmission) low pressure hydraulic system and via a proportional solenoid valve fitted to the right-hand hydraulic cover plate. A transfer pipe hydraulically links the right-hand hydraulic cover plate and the clutch support (32). Pressurised oil enters the unit (9) through hole P and then flows to the rear of the piston (10) via an internal channel. It pushes the piston, which compresses the discs (17) and the intermediate plates (14). The intermediate plates are attached to the bell housing (15) by lugs. The discs are splined to the hub (21). The movement is then transmitted to the rear PTO driving gears via a shaft (35). When the clutch is engaged, the PTO brake piston located in the rear housing is at rest and releases the lower PTO shaftline.

Clutch disengaged position
If the solenoid valve is no longer supplying the rear PTO clutch, the piston (10) is returned against the unit (9) by the spring (18). The oil in the piston chamber is directed to the return by the solenoid valve. The valve ball (8) leaves its seat, thus assisting the decompression of the chamber.


Parts list 
(1) Circlip (2) Ball bearings (3) Sealing ring (4) Ring (5) Seal rings (7) Ball bearing (8) Valve (9) Clutch unit (10) Piston (11) "O" ring (12) Belleville progressivity washers (13) Spring support (14) Intermediate plates (15) Bell housing (16) Screw (17) Discs (18) Spring (19) Spring seat (20) Snap ring (21) Drive hub (22) Ball bearing (23) Chamfered washer (24) Countersunk screw (25) "O" ring (26) "O" ring (27) Sleeve (28) Gear (29) Restrictors (31) Circlip used for oil deflector (32) Clutch support (35) Shaft
Legend
A Details
L Lubrication groove
P Low pressure groove (17 or 21 bar)
P1 Gear with spur cut teeth (GTA1540 tractor transmission)



Disassembling and reassembling the clutch

Remove the clutch. Separate the clutch from its support.


Remove the seal rings (5). If necessary, discard them.
Remove the screws (16). Remove:
- the bell housing (15);
- the discs (17) and intermediate plates (14);
- the drive gear (28)
Secure the front part of the clutch unit (9) in a vice fitted with protective jaws.
Remove the screw (24), using a makeshift tool to hold back the spring (18). Remove the chamfered washer (23).


Gradually release the spring (18) using the tool. Remove:
- the hub (21);
- the seat (19);
- the spring (18);
- the support (13);
- the Belleville progressivity washer (12).
Remove the piston (10) by firmly striking the clutch unit against the wooden edge of a workbench or failing that, against block of a similar nature. Remove and discard the "O" rings (11), (25) and (26). If necessary, remove the circlip (31) (oil deflector).
Extract or drive out:
- the bearing (2) on the support (32);
- the bearing (7) on the unit (9), visually noting the positioning of its sealed face;
- the bearing (22) by first removing the snap ring (20).

Preparing for reassembling 
Clean and check all components. Replace those that are defective. Check the clearance of the valve ball (8) by vertically and rapidly shaking the unit (9): rattling against the unit should be heard.
If removed, press fit the sleeve (27) in the unit (9). Before fitting, the fitted section of the sleeve (27) must be lightly smeared with Loctite 648 or equivalent. Clean off any excess Loctite. Check that the various hydraulic ports are not obstructed after the fitting process.
Using a press and a suitable fixture in contact with the external surface of the bearing (22), Install the bearing up to the shoulder of the hub (21).
Install the snap ring (20).
Position the sealed face of the bearing (7) towards the unit (9). Using a press and a suitable fixture in contact with the internal surface of the bearing (7), Install this bearing against the unit (9).
Using a press and a suitable fixture in contact with the external surface of the bearing (2), Install the bearing up to the shoulder of the support (32).
After fitting, check that the bearings turn correctly.

Install the circlip (31) (oil deflector).
Lubricate and Install the new seals (11) (25) (26) on the sleeve (27) and piston (10) respectively.
Install the piston using a soft hammer, checking during the fitting process that there are no fragments of seal on its rim.


Reinstall:
- the Belleville progressivity washer (12);
- the support (13);
- the spring (18);
- the spring seat (19).
Reinstall the pre-assembled hub (21), using the tool used during disassembly to progressively compress the spring (18).
Secure the front part of the clutch unit (9) in a vice fitted with protective jaws.
Position the chamfer of the washer (23). Position this washer in the drive hub (21). Lightly smear the thread of the screw (24) with Loctite 270 or equivalent. Tighten this screw to a torque of 24-28 Nm.
If the clutch discs (17) have been replaced, the new discs must be soaked for approximately one hour in clean transmission oil.
Stack the new or reused discs and intermediate plates (14), starting with an intermediate plate against the spring support (13). Install the discs and intermediate plates alternately until the number removed during disassembly is reached.
Reinstall the bell housing (15) and the drive gear (28) in the correct position.
Lightly smear the thread of the screws (16) with Loctite 242 or equivalent. Tighten these screws to 25.5-34.5 Nm. Install the seal rings (5).
Reconnect the clutch and its support. Install the assembly.