Park lock of tractor equipped with powershift gearbox


The Park lock system, fitted inside the centre housing, comprises a ratchet (17) and a toothed sleeved (15), integral via splines with the drive pinion and the lower shaft connected to the gearbox. This system is activated by a control unit (3) attached to the right-hand side of the housing and through a spring loaded control rod. The Park lock is only fitted to transmissions equipped with a Full Powershift gearbox.


Operation

Engaged position (speed control in position P)
- When the tractor is halted with the engine running, the Park lock provides a mechanical locking of the transmission. In the engaged position, the solenoid valve (7) is not activated and the system functions in a purely mechanical manner.
- Spring (10) pushes piston (1) towards unit (3). The control rod (11) screwed into the piston drives the links (13) that engage ratchet (17) in the toothed sleeve (15), thus locking the lower transmission shaft line.
- With the engine halted, the Park lock is engaged automatically.

Disengaged position (hydraulic activation)
- When the speed control is placed in the P or N position, the electronic unit (TC) controls solenoid valve (7) that supplies control unit (3) which disengages the Park lock. The pressure in the piston chamber (1), acting upon the front face of the piston, compresses spring (10) and frees ratchet (17) from the toothed sleeve (15).
- The electronic unit (TC) is informed through the position of switch (19) (see section 11).


Parts list
(1) Piston (2) O’ring (3) Control unit (4) Bolt (5) O’ring (6) Special bolt (7) Solenoid valve (8) O’ring (9) Nut (10) Spring (11) Control rod (12) Split pin bolt (13) Links (15) Toothed sleeve (16) Pin and washer
(17) Ratchet (18) Seal(s) (19) Switch (20) O’ring (23) Non-return valve

Version without Park lock
(24) Plug (25) Plug (26) Threaded plug
D : Disengaged position
E : Engaged position

Unlocking the system and positioning the special bolt

- The Park lock system must be unlocked before carrying out certain maintenance operations on the tractor or when the hydraulic or electronic circuits of the Park lock system fail.

Unlocking
Take off nut (9) and turn the special bolt (6) clockwise until piston (1) comes into contact with the shoulder of the housing.


Action obtained
- During this operation, the control rod (11) is moved to the right and compresses the spring (10) freeing ratchet (17) from the toothed sleeve (15).


Restoring the initial position of the special bolt
- After any intervention on the special bolt (6), it is important to restore it in its initial position, i.e. completely unscrewed and locked at a torque of 40 - 50 Nm in order to ensure both the correct operation of the Park lock system and oil tightness of its control unit (3).
Using wrenches, hold the bolt in the previously stated position and tighten nut (9) against the unit housing to a torque of 85 - 115 Nm.

Removing and refitting the sleeve

Uncouple the tractor between the gearbox and the intermediate housing.
Disengage the Park lock system and remove the creeper drive unit.
Visually locate the position of the sleeve and remove it. If necessary, take out the snap ring located inside it. Clean and check the components. Replace any defective parts. If previously removed, replace the snap ring.
Check that the sleeve slides easily on the drive pinion and on the lower shaft coming from the gearbox. Place the sleeve in its final position on the drive pinion, the long part turned towards the pinion. Refit the creeper unit.
Couple the tractor between the gearbox and the intermediate housing.
Place the special bolt (6) in its initial position.

Disassembling the control

Immobilise the tractor. Chock the front wheels. Chock between the frame and the front axle. Remove the rear wheels or place them in the wide track position. If the wheels are removed, position axle stands. Remove the left and right-hand hydraulic covers.


Disconnect solenoid valve (7) fitted on the Park lock unit (3).
Remove two diametrically opposed bolts (4) and screw instead two sufficiently long M6 x 100 threaded rods, fitted with nuts and washers, to make contact with unit (3). Remove the two other bolts. Loosen nut (9) and turn the special bolt (6) several turns clockwise to slightly free the lower pin bolt (12).
Through the opening of the right-hand side cover, take out the pin and remove the bolt. Progressively and alternately unscrew the wing nuts "E" on the two threaded rods in order to release the spring (10).


Remove unit (3), piston (1) fitted with O’ring (8), rod (11) and spring (10).
Recover the O’rings (2) (20). Through the opening of the left-hand side cover, remove the pin from bolt (16) and thus remove ratchet (17).
If necessary, remove the switch (19) fitted with its seal (18).

Reassembling the control

Clean and check the components. Replace any parts found to be defective.
Refit the ratchet. Carry out operation in reverse order.
- Limit the axial clearance of pin bolt (16) to the maximum (tolerance 0 mm to 2 mm), by if possible placing a washer on the pin bolt between the housing and the pin.
If fitted, screw piston (1) on to rod (11) with its threads lightly smeared with Loctite 270 and tighten to a torque of 50 - 70 Nm. Using a punch, mark the external face of piston (1) and rod (11) with two diametrically opposed marks.


Replace and lubricate the O’rings (2) (8) (20). In the opening of the intermediate housing, position piston (1) with rod (11) and spring (10) by aligning the hole of the shaft with the two links (13). Use unit (3) to push on piston (1) and compress spring (10) by using the threaded rods, washers and
wing nuts used for disassembly. Fit pin (12) with its retaining pin turned towards the front. Fit and tighten the two bolts (4) to a torque of 10 – 14 Nm.
Remove the nuts, washers and threaded rods. Fit the other two bolts and tighten to the previously indicated torque. Refit the right- and left-hand side covers. Reconnect solenoid valve (7).
Remove the axle stands (if used) refit the wheels or place them in their initial position. Carry out the tightening of nuts and bolts to their indicated torque.
Check the correct operation of the dashboard indicator lamp and the display of the letters P and N in relation to the speed control.
Check the oil tightness of the control unit (3).

Torques
- Switch (19): 20 Nm
- Bolts (4): 10 - 14 Nm
- Solenoid spool valve (7): 18 - 20 Nm
- Knurled nut (solenoid valve): 3 - 4 Nm or manual tightening
- The letter "R" indicates the unit (3) oil return port.