ZF Front axle - differential

The tractors are fitted with ZF front axle APL 5052. This ZF front axle does not have a hydraulic differential lock similar to the “conventional” front axles. This front axle is fitted with an limited slippage system which consists of friction disks (35) and intermediate plates (36) integral with the left and right-hand side output sun gears (34) and the half-housings of the differential (17) (37). This type of differential does not have a total self-locking function. The crownwheel / drive pinion assembly is fitted in housing (7) and comprises two split bearings (18) held by bolts. The drive pinion, located at the rear of the housing, bears on two taper roller bearings. Its position is adjusted by shim (23) inserted between the housing and the bearing cup (21). The pre-loading of the bearings is obtained by shim (9) placed between the shoulder of the drive pinion and bearing cone (11). Both the pre-loading of the differential housing assembly and the drive pinion backlash is adjusted by castellated nuts (4) fitted on either side of the differential housing. The housing oil tightness is provided by a lip seal (12) fitted in flange (13).

ZF front axle differential APL 5052 Parts list 
(1) Axle housing (2) Breather (3) Split pin (4) Castellated nut (5) Bearing cup (6) Bearing cone (7) Housing (8) Bush (9) Shim (10) Bearing cup (11) Bearing cone (12) Lip seal (13) Flange (14) Bolt (15) Ring (16) Bolt (17) Half-housing (18) Half-bearing (19) Crownwheel (20) Drive pinion (21) Bearing cup (22) Bearing cone (23) Shim (bevel gear) (24) Planetary gear pin (25) Planetary gear (26) Dust cover (27) Spherical washer (28) Plate (29) Washer (30) Nut (31) Level plug and seal (32) Drain plug and seal (33) Bolt (34) Sun gear (35) Friction disks (36) Intermediate plates (37) Half-housing (38) Washer (39) Bolt (40) Bolt (41) Tab washer (42) Bolt

Removing the swivel housings

Take off:
- the swivel pin grease nipples
- the arm on the upper swivel pin
- the cover on the lower swivel pin
Visually note the location of the shims and bearing cones.
- A 45º grease nipple is fitted on the lower swivel pin.
- Take care not to damage the seals and dust covers fitted on the axle housing when the removing the universal drive shaft.

Removing the axle nose

Take out bolts (33). Mark the position of the differential housing on the axle housing (1) by two opposing paint marks “T” in order to later refit the assembly in its original position. Lift and remove the housing using an appropriate fixture.

Removing and install – disassembling and reassembling the ZF differential housing and crownwheel

Mark the position of the half-bearings (18) on the housing (7) using two opposing paint marks “T” so as to be able to replace them in their original positions on reassembly.

Take off and discard the two split pins (3). Unscrew the castellated nuts (4) using a suitable locally manufactured tool.
Cut and remove the steel wire “F” that locks bolts (40). Take out the bolts fitted with their washers. Remove the half-bearings and bearing cups (5). Take out the ZF differential housing from the housing (7) 
- If they are to be re-used, match the cups and cones together.

 - The bearing cups and cones must be lubricated with oil having an 80W/90 viscosity grade before assembly.
Place the differential housing in the housing with the bearing cones.
Position the half-bearings in accordance with the previously made marks.
Install bolts (40) equipped with their washers and tighten them to a torque of 150 Nm.
Lock the bolts by tying them in pairs using new steel wire. Twist the ends of the wire together correctly.
Carry out the shimming of the differential housing bearing cones and cups (6) (5). Adjust the crownwheel and drive pinion backlash.

Disassembling the ZF differential housing

Place the differential housing on a workbench with the crownwheel (19) turned downwards.
Mark the position of the ZF differential half-housings (17) (37) with two opposing paint marks. Remove the bolts fitted with their washers.
Separate the half-housings while holding the upper sun gear (34) comprising:
- the disks
- the intermediate plates
- the tab washer
One by one, separate the disks (35), the intermediate plates (36) and tab washer (41) from the sun gear (34) while visually noting their location.

Take apart the planetary gear pins (24), the planetary gears (25) and spherical tab washers (27).

Take out the lower sun gear (34) and one-by-one remove the disks, intermediate plates and halfhousing (17) tab washer and visually note their location.
If required, extract the bearing cones from each halfhousing using a locally manufactured tool.

Disassembling the crownwheel
- The replacement of the crownwheel necessarily requires replacement of the drive pinion. Both parts have the same number engraved on them.
- They must be fitted as matched pairs.
Take out bolts (16) and extract the crownwheel from the half-housing (17).

Reassembling the crownwheel
Clean the mating faces of the new crownwheel and half-housing. Check that there is no traces of shock.
Using an oven only, heat the crownwheel to a temperature of 95º C and insert it thrusting against the half-housing.
Degrease the new bolts and lightly smear the threads with Loctite 270 or its equivalent and screw them into the crownwheel. Tighten all the bolts to a torque of 190 Nm.

Reassembling the ZF differential housing
- If disassembled, insert the new or re-used bearing cones on the shoulder of each half-housing.

Reassembling the differential limited slip lock
The friction discs (35), intermediate plates (36) and tab washers (41) must be replaced.
Pile and alternate four disks (35), five intermediate plates (36) and one tab washer (41) on the lower sun gear beginning with the tab washer (41) which has a greater thickness than the friction disks.

Special point
- The shiny face of the tab washer must face the sun gear.
Return the previously assembled sun gear to the half-housing (17).
Assemble the four planetary gears (25), the four spherical washers (27) on the two pins (24) then place the assembly in the half-housing by placing tabs “E” of each spherical washer in contact with the half-housing (17).

Pile and alternate the friction discs, intermediate plates and tab washer on the upper sun gear (34).

Return the previously assembled sun gear to the half-housing (37).
Check that the tabs of the spherical washers (27) are in contact with the half-housing (17).
Place the half-housing (37) according to the paint marks made during the disassembly of half-housing (17) while holding manually the upper sun gear and pile of friction disks, intermediate plates and thrust
washer. Provisionally fit four diametrically opposed bolts (39) with their washers and tighten to a torque of 120 Nm.

Adjusting the differential lock
- In order for the limited slip differential housing to function correctly there must be a space of 0.1 to 0.2 mm between the friction disks and the intermediate plates. For this, carry out the following adjustment.
- The adjustment is carried out on each sun gear.

Sun gear opposite the crownwheel
Place the index of a dial gauge on tab washer (41) which is accessible via one of the four ports machined in the half-housing (37) (Fig. 14).

Set the needle of the dial gauge to zero.
Manually apply pressure from top to bottom or vice versa on the sun gear (34) through the lateral recesses in the half-housing and calculate the gap after reading the dial gauge. If the gap is between 0.1 mm and 0.2 mm the adjustment is correct. Otherwise, replace the intermediate plates (36) by thicker or thinner plates in order to obtain the previously stated clearance.
- There are three thicknesses of intermediate plates referenced in the Spare Parts catalogue: 1.8 mm, 1.9 mm,  2 mm.
Use the previously mentioned method for the sun gear on the crownwheel side.

- The half-housing (17) does not have lateral recesses. Manually access the sun gear via the central bore.
When the adjustment phase is completed, take out the four bolts and washers that were provisionally tightened and then fit all the bolts (39), with their threads lightly smeared with Loctite 242 or its equivalent. Tighten the bolts to a torque of 120 Nm.
Manually check for the rotation of the sun gears using a locally manufactured tool matching the splines on the sun gears.

Shimming the differential housing and adjusting the backlash

If replacement is necessary of the housing (7), 17 bevel gear and drive pinion, carry out a shimming of the differential housing and an adjustment of the backlash.

Preparation for shimming
Reinstall the differential housing in the housing.
Place the axle nose vertically on an appropriate fixture.

Shimming the differential housing
Install a dial gauge, the index touching the machined end of the half-housing (17). Before carrying out shimming, check that the crownwheel does not overload the drive pinion.
Using two diametrically opposed levers, exert an axial pressure on the differential housing first frontward then rearwards in order to correctly seat the cones (6) in bearing cups (5).
Screw down the castellated nut (4) facing the crownwheel to remove the axial clearance at the differential housing. During the operation, check for the correct rotation of the assembly.
After removing the clearance, turn the previously mentioned nut by two additional notches in order to apply the correct pre-loading on bearings (5) (6).

Adjusting the backlash
- the adjustment of backlash is carried out after shimming the differential housing. It ensures the reliability and correct operation of the bevel gear.

Place the index of a dial gauge half way down a tooth on the crownwheel (19).
Move the differential housing towards the drive pinion by successively screwing and unscrewing nuts (4) by the same amount.
With care, move the crownwheel forward and backward without actually turning the drive pinion in order to read the value of the backlash on the dial gauge.
Carry out three measurements at three equidistant points on the crownwheel and calculate the average of the three readings, so as to obtain a backlash corresponding to the decimal number stamped on the rim of the crownwheel within a tolerance of ± 10%.

Example: 291 / 0.18
- 291 = matching set number
- 0.18 = correct value of backlash
When the correct backlash has been obtained, fit and bend the new pins (3) in order to immobilise the castellated nuts (4).
- If the notch of the nut is not aligned with the hole of the half-bearing pin, continue tightening until the next notch.
- Manually check for the rotation of the differential housing.

Checking the bearing of the crownwheel on the drive pinion
Using a marker product, mark the teeth of the crownwheel (19) at three equidistant points.
Turn the crownwheel several times and visually check the traces of the crownwheel on the drive pinion. If the traces are doubtful, check or adjust the backlash and/or bevel gear distance again.