Rear axle differential with standard bevel gear and hydraulic mechanical lock


Some tractors are equipped with an identical centre housing. The intermediate housing differs depending on the type of gearbox.

Specifications
- Heavy gearbox
- narrow intermediate housing
- AG 150 Powershift gearbox
- wide intermediate housing
- AG 250 Powershift gearbox
- wide intermediate housing (hypoid version)

Some model of tractors are fitted with a standard bevel gear and either a multidisc or hydraulic mechanical differential lock (depending on version).


Construction
The bevel gear, its rotation provided by the gearbox output shaft, drives the rear axle. The helical drive pinion is supported by two taper roller bearings mounted in opposition. The bearing cone (7) is force fitted on the drive pinion, and cups (2) (10) are likewise force fitted into the intermediate housing (19) and bearing carrier (13). The bearing cone (1), mounted free on the drive pinion, allows to fit shims (3) required for shimming. The crownwheel is fastened to the differential housing by rivets. 
The rear axle differential assembly rotates on two taper roller bearings supported by two lateral carriers centred by bushes (25) (40) and fixed by bolts to the housing. The rear axle differential assembly is formed by two halves holding four planetary gears and two sun gears. The drive pinion, which bears the 4 WD drive pinion (17) (if fitted), is located in the intermediate housing. The adjustment of its position is carried out by shims (12) fitted between the differential lock carriers, the bearings (13) and the housing. The pre-loading of the bearings is obtained by shim(s) (3) fitted between the bearing cone (1) and the thrust washer (4). The pre-loading via shimming of the rear axle differential assembly is carried out via the intermediary of a deflector (55) (equally serving as an adjustment shim) placed between bearing cup (57) and the left-hand differential lock carrier (38). Backlash between the drive pinion and the crownwheel is obtained by using shims (59) inserted between cup (32) and the differential half-housing (23).


Differential lock
- The left-hand differential lock carrier houses the differential lock mechanism
- The system consists of a piston (58) and a mobile dog (48) integral via splines with the input sun gear in the left-hand side trumpet housing.
- The piston acts upon the mobile dog when the 17 bar hydraulic circuit is pressurized via the solenoid valve fitted to the right-hand cover. The piston moves and pushes the mobile dog while compressing spring (47).
- The front teeth of the mobile dog engage with a fixed dog (46) integral with the differential half-housing (23). In this position, the input sun gears of the right-hand and left-hand trumpets then turn at the same speed. When the pressure is released, the mobile dog returns to its initial position under the action of the spring.


Parts list
(1) Bearing cone (2) Bearing cup (3) Shim(s) (4) Thrust washer (5) Circlip (6) Intermediat plates (handbrake) (7) Bearing cone (8) Bolt (9) Drive pinion (10) Bearing cup (11) Bolt (12) Shim(s) (13) Bearing carrier (14) Discs (15) Handbrake unit (16) Mechanism (17) 4 WD drive pinion (if fitted)
(18) Nut (19) Intermediate housing (20) Deflector (22) Crownwheel (23) Differential half-housing (24) Rivets (25) Centring bush (26) Bolt (27) Right-hand carrier (28) Spherical washer (29) Planetary gear (30) Sun gear (31) Bearing cone (32) Bearing cup (33) Brace (34) O’rings (35) Shouldered bush
(36) Fixed coupler (37) O’ring (38) Left-hand carrier (39) Bolt (40) Centring bush (41) Bolt (42) Transfer tube (43) O’ring (44) Union (45) Centre housing (46) Fixed dog (47) Spring (48) Mobile dog (49) Friction washer (50) O’ring (51) O’ring (52) Circlip (53) Finger (54) Bearing cone (55) Deflector (shim) (57) Bearing cone (58) Piston (59) Shim(s) (61) Shouldered bush

Removing and install the left hand differential lock carrier, disassembling and reassembling the lock assembly

It is possible to gain access to the following differential lock components by removing only the left-hand trumpet housing:
- differential lock carrier (38)
- piston (58)
- seals (50) (51)
- spring (47)
- mobile dog (48)

Removing the left-hand differential lock carrier (38)
Remove the left-hand trumpet housing.
Disconnect the hydraulic feed pipe. Unscrew union (44) and raise the transfer pipe (42). Remove the brake piston.
Alternatively, unscrew bolts (39) on the differential lock carrier. Place two diametrically opposed guide studs "G" on the housing. Progressively extract the differential lock carrier through the tapped holes and two bolts "V" in order to progressively release the spring (47).


Remove the differential lock carrier and recover the spring, the mobile dog, the friction washer, possibly cup (57) and deflector (55) (shim).



Check for the presence of centring bush (40), the correct positioning of deflector (55) (shim) and cup (57). Install new o’rings (34) (37).
Place the friction washer (49) and spring (47) on the mobile dog. Install the assembly in the piston. Slide the differential lock carrier onto the guide studs "G" previously fitted into the housing by positioning the hydraulic port of the differential lock upwards and holding the spring in position.
Alternately and uniformly tighten the four bolts (39) to a torque of 100 - 130 Nm. Remove the guide studs. Install and tighten the other bolts to the same torque.
Install transfer pipe (42) and connection (44). Reinstall the brake piston.
Check the oil tightness of seal (34) on differential lock carrier (38).
Reinstall the left-hand trumpet.

Disassembling the lock assembly 
Remove the differential lock carrier.
Take out cup (57). Note the orientation of the deflector (55) (shim) and remove the differential lock carrier. Take off circlip (52).
Drive out piston (58) from the differential lock carrier using a compressed air jet.


Take off the o’rings (37) (50) and (51). If necessary, unscrew the finger (53).

Check and clean the components. Replace any parts found to be defective.
If finger (53) has been removed, lightly smear with Loctite 221 then refit and tighten it in the differential lock carrier (38).
Coat the o’rings (50) (51) with miscible grease, in order to place them correctly in the bottom of their respective grooves.
Using a plastic hammer, insert the piston (58) into the differential lock carrier (38) while respecting the location of the finger (53).


Install circlip (52), deflector (55) (shim) while respecting its orientation. Place bearing cup (57).
Reinstall the differential lock carrier on to the centre housing.
Test the oil tightness of the seals (50) (51) and differential lock carrier (38) mounted on the locking piston.
- If the piston (58), seals (50) (51) or carrier (38) have been disassembled, it is recommended to carry out an hydraulic test of the whole hydraulic assembly and of the transfer tube after reassembly.



Hydraulic test
- Use a pressure gauge that has previously been tested for pressure tightness.
- Supply the circuit with compressed air up to around 5 bar, in order to check the reaction of the piston. Adjust the pressure to approximately 0.3 bar. Carry out the hydraulic test.
- Close the valve. For approximately 1 minute, no drop in pressure must be observed on the pressure gauge.
When the test is completed, remove the pressure gauge and fit the original pressure pipe. Reinstall the trumpet housing.

Removing and install the right hand differential lock carrier

- The access to the right-hand differential lock carrier (27) is similar to that of the left-hand differential lock carrier (38).
- In order to maintain the crownwheel assembly in position, it is recommended to screw two diametrically opposed guide studs "G" into the tapped holes holding the differential lock carrier on to the housing, with their ends abutting against the differential halfhousing (23). Remove bolts (26).
Using the two ‘V’ bolts in the tapped holes of the carrier, extract the latter from the housing and remove it, as described in the procedure used for the left-hand carrier. Check for the presence of centring pin (25) and O’ring (34).


Uniformly and alternately, tighten the four bolts (26) to a torque of 100 - 130 Nm. Take out the guide studs. Install and tighten the other bolts to the same torque. Check the oil tightness of seal (34) on carrier (27).