Standard bevel gear differential and multidisc lock - planetary gears, sun gears and crownwheel


Removing and refitting the planetary gears and sun gears and disassembly and reassembly the crownwheel


Remove the differential unit. Remove the locking system and unit (46).

Removal 
Separate the half-housings (23). These components both bear the same number. They must be fitted as pairs. Remove the sun gears (30) fitted with friction bushes (35) (61), the planetary gears (29), washers (28) and differential brace (33).


If necessary, drive cup (32) off the half-housing (23) and recover the shim(s) (59). Extract and discard deflector (20).

Disassembling the crownwheel
The replacement of the crownwheel automatically requires replacement of the drive pinion. Both parts bear the same number and they must always be fitted as pairs. The original factory parts are assembled using rivets. 


During repairs, these rivets are replaced by nuts and bolts and are referenced in the spare parts catalogue. Centre punch each rivet (24) (on toothed side of crownwheel). Using a 5 mm drill, drill out the rivets to a depth of 12 mm. Carry out a second drilling using a 12 mm drill to the same depth. Drive out the rivets using an appropriate drift.

Refitting the crownwheel
Clean the mating faces of the new crownwheel (22) and differential half-housing (23) as well as their nuts and bolts. Lightly smear the first few threads of the bolts with Loctite 270 and place them in the crownwheel and housing. Tighten the nuts to a torque of 150 - 200 Nm.

Refitting planetary gears and sun gears
- If the friction bushes (35) (61) have been replaced, insert the new bushes lightly smeared with Loctite 638 or equivalent, using a suitable fixture.
- Check after insertion that the lubricating ports have not been blocked by Loctite.
If necessary, insert the deflector (20) and cup (32).
Refit the planetary gears and sun gears. Carry out operations in reverse order.
Lightly smear bolts (41) with Loctite 270 or its equivalent and tighten them to a torque of 130 Nm. Refit the hub, the intermediate plates, discs and cover.
Refit the differential unit and the brake pistons. Finish the refitting of the different assemblies.

Adjusting and checking the backlash

The backlash between the crownwheel and drive pinion ensures reliability of the bevel gear and the correct operation of the assembly. This clearance must be checked after:
- adjusting the bevel gear distance
- shimming the differential unit.

Disassembly
- Using an appropriate extractor, remove cup (32) and discard the deflector (20).
- The thickness of the shim(s) E required to obtain the correct backlash is calculated as follows: E = Dc + 0.10 mm. E: thickness of shim(s) (59) to be fitted Dc: crownwheel offset
- The Dc (example shown: -0.40) engraved on the external diameter of the crownwheel after the pairing number and letter ( 39 K) may range between 0 and -0.60 mm.


Special point
- When calculating E do not take the negative sign preceding the Dc into consideration.
Place the previously selected shim(s) (59) in the bore of the half-housing (23). Insert the deflector (20) and cup (32).

- The deflector serves as a guide for centring the shims. It is inserted using the cup and an appropriate locally manufactured tool. This method allows the deflector to rest against the cup both during and after its insertion.
- When the operation is completed, check that the cup is thrusting on the shim(s) and in contact with the deflector. Refit and shim the differential unit.

Checking
- Couple and temporarily fix the intermediate housing to the centre housing using several diametrically opposed bolts tightened to a torque of 540 – 680 Nm.
- With the PTO housing taken off, through the rear opening of the centre housing (45), place the index of a dial gauge half way across the length of a tooth of the crownwheel.
- Check that the backlash is between 0.15 mm and 0.45 mm. Carry out this check at three points around the crownwheel.

- If the backlash is incorrect, the adjustment principle is to reduce or increase the thickness of shim(s) (59). In this case, select and fit a different thickness of shim(s). Carry out the shimming of the differential unit again in order to obtain the pre-loading of bearings (31) (32) and (54) (57). Check a second time the backlash between the drive pinion and the crownwheel.
- When the final adjustment has been obtained, go on with the refitting operations.

Shimming the differential unit

If the centre housing (45), crownwheel, taper roller bearings and carriers (27) (28) have been replaced, carry out shimming of the differential unit. Check beforehand that the shim(s) (59) used for the backlash are fitted in the half-housing (23) and cup (32).

Shimming preparation
Place the differential assembly previously fitted with bearing cone (54) in the housing using sling ref. 3378116M1. Screw two diametrically opposed guide studs into the centre housing. Insert carrier (27) fitted with a new O’ring (34) using four bolts (26). Remove the guide studs. Complete the refitting of the other bolts and tighten to a torque of 100 - 130 Nm.
Remove bearing cone (54) and shim(s) (55) from carrier (38).
Slide bearing cone (54) on tool, ref. 3378117M1, adapted for the standard differential unit with multidisc lock. Using two bolts, fix the tool onto the housing.


Tighten the centre bolt to 10 Nm. Turn the crownwheel several times to seat the cones correctly in the cups. Check the tightening torque of the centre bolt again. Dimension to be measured on the housing (45).


Using an appropriate depth gauge, measure dimension "B" and determine dimension "C" between bearing cup (54) and the thrust face of the carrier (38) on the housing: C = B – 10 mm (10 mm is the thickness of tool, ref. 3378117M1). Dimension to be measured on carrier (38).


Measure dimension "Y" using an appropriate depth gauge and rule.
Calculate distance "E" between the thrust faces of bearing cup (54) and carrier (38): E = C – Y. Fill in space "E" with a thickness of shims (55).


In space "E", add additional shims between 0.05 mm and 0.15 mm, so as to obtain a P2: P2 = 0.05 mm to 0.15 mm. Remove the tool and bearing cup (54).


On carrier (38), place the shims determined in operation. Centre the differential assembly, carry out operations.