Reassembly the Carraro differential unit


Mount the new tapered roller bearings on the half-bearings using special tool ref. CA115093 and a hammer.
Position one of the half bearings on a workbench and install the internal parts (thrust washer, sun gear, planet gears, spider) as shown in the figure. Insert the pin into its housing, holding the planet gears and spider correctly in place.
Lock the pin by inserting the locating dowel in the hole provided on the bearing and pin. Turn the pin manually to align the hole of the dowel with that of the bearing. Definitively position the locating dowel.
Position all the internal parts in the bearing: planet gears, discs and counter-discs.
Install new "O" rings in the seatings provided on the piston and on the differential cover plate. Insert the piston and fit the cover plate in the differential housing.
Apply a film of Loctite 476 between the bevel ring gear and the differential housing surface. Position the bevel ring gear on the cover plate, apply Loctite 270 to the threads and attach the assembly, tightening the screws to a torque of 70 Nm.

Install the differential housing assembly

Install the external tapered roller bearing cups on the two differential bearings and install the washer and spacer on the crownwheel and pinion side with new seals, previously smeared with a thin layer of grease.
Before positioning the differential unit in the differential housing, install a new seal B and washer A at the bearing base on the bevel ring gear side, over the oil hydraulic port. Install the unit assembly on the differential housing. Take care not to invert the external cups of the tapered roller bearings and ensure that the bevel ring gear assembly is fitted on the correct side.


Move the differential assembly so that the bevel ring gear can be positioned on the pinion. Ensure that all rings E are in position in their seatings and place both half-bearings D on their seats, following the marks made during disassembly. Lock the two half-bearings with their screws C.


Assemble and tighten the two adjustment nuts in the differential housing using special tools ref. CA119030 and CA119149 to eliminate the backlash and slightly preload the differential bearings. As the two nuts are different, take care to return them to their original positions relative to the bevel ring gear. Check that the bearings are correctly mounted in their seats, and, if necessary, tap them gently with a rubber hammer to secure them in place. Place a dial gauge with a magnetic stand on the differential housing and move the dial gauge feeler pin until it comes into contact with a ring gear tooth at a 90° angle.
Lock the pinion and move the ring gear alternately to the right and left, using the dial gauge to measure the backlash between the pinion and the ring gear. Repeat the operation on at least two teeth, turning the ring gear, to calculate an average value. Check that the measured backlash value is within the permissible tolerances: 0.18 to 0.23 mm.
Fine-tune the shimming by adjusting the two nuts with special tools CA119030 and CA119149.

When tightening nuts, always remember that:
- if the measured backlash is lower than the permissible tolerance, the nut on the bevel ring gear side must be loosened and the opposite screw must be screwed to the same value.
- if the measured backlash is higher than the permissible tolerance, the nut on the side opposite the bevel ring gear side must be loosened and the screw on the other side must be screwed to the same value.
When the backlash between the pinion and ring gear has been adjusted, check that the bearing preload of the differential unit is minimal. Repeat the sequence of steps described above until the required conditions are met.
Once the correct backlash has been obtained between the pinion and ring gear, measure the total bearing torque T (pinion-bevel ring gear system). The measured value must remain within the following limits: T= (P+1.82) to (P+2.12) N.m where P represents the actual measured pinion torque. All torques must be measured without the seal. If the measured value is outside the permissible tolerances, check the assembly of each part carefully and adjust the differential housing adjustment nuts:
- if the total torque is lower than the permissible values, tighten both nuts identically without modifying the backlash between the pinion and ring gear
- if the total torque is higher than the permissible values, loosen both nuts identically without modifying the backlash between the pinion and ring gear.

To test the marking of the crownwheel and pinion teeth, apply a tiny amount of paint to the ring gear.
This marking test must be carried out systematically on the bevel ring gear teeth and on each face.
OK = Correct contact


If the crownwheel and pinion are adjusted correctly, a uniform layer of paint is left on the surfaces of the teeth:
- Z: Excessive contact at the tip of the teeth
Move the pinion closer to the ring gear then move the ring gear away to correct the backlash.
- X: Excessive contact at the base of the teeth.
Move the pinion away from the ring gear, then move the ring gear closer to correct the backlash.

Corrective action :
1 Move the pinion in the direction of the arrow to adjust an X type contact.
2 Move the pinion in the direction of the arrow to adjust a Z type contact.


When the shimming procedure is complete, Install the nut retainers with their screws and tighten to the required torque (13 Nm) using a torque wrench. The nut and its corresponding counter-nut are different on the ring gear side and the opposite side of the differential unit; turn the nuts slightly to align them with their retainers.


Tighten the screws of the two half-bearings with a torque wrench to the required torque (266 Nm).

Before bringing two surfaces into contact, ensure that both are perfectly clean. Degrease and clean them with suitable cleaning products. Apply a thin film of Loctite 510 to the mating surface between the axle beam and the differential housing. Install the differential housing on the axle housing and screw to the required torque (169 Nm).
Install a new previously lubricated seal C on the end of the pinion using the special tool ref. CA119148 then install the flange A. Position the flange screws B with their respective nuts. Tighten the screws and nuts with a torque wrench to the required torque (57 Nm).