Flush gearbox parts thoroughly before inspecting. This will make it easier to identify wear and damage to parts.
Check if there are any damages on the teeth of the main gears and if the contact spots on the working surfaces of the teeth are correctly located
In case of unacceptable wear, replace the parts with new ones; if the engagement is wrong, find the cause.
In spare parts, the drive and driven gears are supplied with a set matched for noise and contact, therefore, if one gear is damaged, both are replaced.
Check the condition of the holes of the satellites and the surfaces of their axis; in case of minor damage to the surface, sand it with a fine-grained sandpaper, and in case of serious damage, replace the parts with new ones.
Check the surfaces of the journals of the semi-axle gears and their bore holes in the differential box, the condition of the holes in the box for the pinion axle.
Repair the found damage, as in the previous operation, if necessary replace worn or damaged parts.
Inspect the surfaces of the half-axle gear washers, repair even minor damage. When replacing washers, select new ones by thickness.
Inspect the pinion roller bearings and differential boxes; they should be free of wear, with smooth working surfaces.
Replace bearings if there is the slightest doubt about their performance, poor condition of the bearings can cause noise and teeth jamming.
Check the crankcase and the differential box for deformations or cracks, if necessary replace them with new ones.
Reliable operation of the gearbox is ensured by strict adherence to the following assembly and adjustment techniques.
Gearbox parts are shown in Figure 1.
Lubricate with transmission oil and install through the windows in the differential box the side gears with support washers and satellites.
Turn the satellites and side gears so that the axis of rotation is aligned with the axis of the hole in the box, then insert the pinion of the satellites.
Check the axial clearance of each half-shaft gear: it should be 0-0.10 mm, and the torque of resistance to rotation of the differential gears should not exceed 14.7 Nm (1.5 kgcm).
With an increased clearance, which is a sign of wear of the differential parts, replace the support washers of the side gears with other, thicker ones.
If the specified clearance cannot be obtained even with the thickest washer, replace the gears with new ones due to excessive wear.
Secure the driven gear to the differential case.
Using a mandrel A.70152, press the inner rings of the roller bearings onto the differential box.
Installing and adjusting the drive gear
The correct position of the drive gear relative to the driven gear is ensured by selecting the thickness of the adjusting ring installed between the end face of the drive gear and the inner ring of the rear bearing.
Select the adjusting ring using a mandrel A.70184 and a tool A.95690 with an indicator. Perform operations in the following order.
After fixing the gearbox housing to the stand, press the outer rings of the front and rear bearings of the drive gear into the housing seats, using mandrels: for the front bearing A.70185, and for the rear bearing - A.70171 (Figure 2).
On a mandrel A.70184 imitating a drive gear, install an inner ring of the rear bearing using a mandrel A.70152 and insert the mandrel into the throat of the gearbox housing (Figure 3)
Install the inner ring of the front bearing, the drive pinion flange and, turning the mandrel to correctly install the bearing rollers, tighten the nut to a torque of 7.85-9.8 Nm (0.8-1 kgcm).
Fix the A.95690 tool on the end of the mandrel 4 and set the indicator, which has divisions of 0.01 mm, to the zero position, installing its leg on the same end of the A.70184 mandrel.
Then move the indicator 1 so that its foot rests on the bearing seating surface of the differential box.
Turning to the left and right the mandrel 4 with the indicator, set it to the position in which the indicator arrow marks the minimum value "a 1" (Figure 4) and write it down.
Repeat this operation on the seating surface of the second bearing and determine the "a2" value.
Determine the thickness "S" of the adjusting ring of the drive gear, which is the algebraic difference between the values "a" and "b":
S = a - b, where:
a is the arithmetic mean distance from the end of the mandrel 1 (Figure 4) to the journals of the differential bearings
a = (a1 + a2): 2
b - deviation of the pinion gear from the nominal position converted in mm.
The amount of deviation is marked on the drive gear (Figure 5) in hundredths of a millimeter with a plus or minus sign.
When determining the thickness of the adjusting ring, take into account the sign of the “b” value and its unit of measurement.
Suppose that the value "a", set using the indicator, is 2.91 mm (the value "a" is always positive), and the deviation "-14" is set on the drive gear after the serial number.
To obtain the "b" value in millimeters, multiply the indicated value by 0.01 mm.
b = –14 · 0.01 = –0.14 mm
Determine the thickness of the pinion shim in millimeters.
S = a - b = 2.91 - (–0.14) = 2.91 + 0.14 = 3.05 mm
In this case, use a 3.05mm shim.
Slide the adjusting ring of the required thickness onto the drive gear and press on with a mandrel A.70152 (Figure 6) the inner ring of the rear bearing removed from the mandrel A.70184. Slide on the spacer sleeve.
When repairing the rear axle gearbox, it is necessary to install a new spacer sleeve if the gearbox housing, main drive gears or drive gear bearings have been replaced.
If these parts remain the same, the spacer sleeve can still be used.
Insert the drive gear into the gear case and install the front bearing inner race, oil deflector, oil seal, drive gear flange and washer on it.
Screw a nut onto the end of the gear and tighten the flange of the pinion gear.
Drive Gear Bearing Adjustment
To limit the axial displacement of the drive gear under operating loads, it is very important to create a preload in its bearings within the specified limits.
The preload is controlled by dynamometer 02.7812.9501 (Figure 7), which measures the moment of resistance to turning of the drive gear.
The torque is determined by the degree of tightening of the bearings. It should be 157–196 N · cm (16–20 kgf · cm) for new bearings, 39.2–58.8 N · cm (4–6 kgf · cm) - for bearings after a run of 30 km or more.
It is necessary to tighten the flange nut periodically by checking with a dynamometer the moment of resistance of the bearings to the rotation of the drive gear. In this case, the moment on the nut can be in the range of 118–255 Nm (12–26 kgf · m).
To check the moment of resistance, put the dynamometer on the adapter sleeve 3 (Figure 8), set the pointer 2 (see Figure 7) to limit the torque per division of the scale corresponding to 196 Ncm (20 kgf clockwise.
While turning the drive gear, the movable indicator 1 should not go beyond the indicator 2 and must show at least 157 Ncm (16 kgfcm).
If the moment of resistance to turning is less than 157 N cm (16 kgf cm), and for bearings after 30 km of run 39.2 N cm (4 kgf check again the moment of resistance to turning of the drive gear.
If the moment of resistance to turning is more than 196 Ncm (20 kgfcm), and for worn-in bearings 58.8 Ncm (6 kgf overload is deformed to a size that does not allow for correct adjustment.
After replacing the spacer sleeve, reassemble with appropriate adjustments and checks.
Installing the differential box
Install the pre-assembled differential case with the outer bearing races in the crankcase.
Install two adjusting nuts 4 (figure 9) so that they come into contact with the bearing rings.
Install the bearing caps and tighten the mounting bolts with a torque wrench.
Preloading the differential box bearings and adjusting the lateral clearance in the meshing of the final drive gears
These operations are performed simultaneously using the A.95688 / R tool and the A.55085 key.
Fasten the device to the gearbox housing with screws 1 and 6, screwing them into the holes for the bolts securing the lock plates of the adjusting nuts.
Along the guide of the device, slide the bracket 7 until the lever 5 touches the outer side surface of the cover and tighten the screw 8.
Loosen screws 1 and 3 (Figure 10) and install bracket 4 so that the indicator foot 2 rests on the side surface of the driven gear tooth at the edge of the tooth, then tighten screws 1 and 3.
Turning the adjusting nuts, pre-adjust the side clearance between the teeth of the drive and driven gears within 0.08–0.13 mm.
The clearance is checked by indicator 2 when the gear 6 is wiggling. In this case, the bearings should not have a preload.
The adjusting nuts must only be in contact with the bearings, otherwise the correct preload measurement will be impaired.
Tighten the two bearing adjusting nuts consistently and evenly, with the differential bearing caps spreading apart and, therefore, increasing the distance "D" (figure 11) by 0.14-0.18 mm.
Having established the exact preload of the differential box bearings, finally check the side play in the meshing of the main gears, which should not change.
If the clearance in the meshing of the gears is more than 0.08–0.13 mm, then bring the driven gear closer to the driving gear or move it back if the clearance is less.
To maintain the set bearing preload, move the driven gear by tightening one of the bearing adjusting nuts and loosening the other by the same angle.
For accurate performance of this operation, watch the indicator 9 (see Figure 9), which shows the value of the previously set bearing preload.
After tightening one of the nuts, the indicator reading will change, as the divergence "D" (see Figure 11) of the covers and the preload of the bearings increases. Therefore, loosen the other nut until the indicator arrow returns to its original position.
After moving the driven gear, using indicator 9 (see Figure 9), check the value of the side clearance. If the clearance is not correct, repeat the adjustment.
Remove the A.95688 / R tool, install the adjusting nut lock plates and secure them with bolts and lock washers.
Spare parts are supplied with two types of locking plates: with one or two lugs, depending on the position of the nut slot.
Adjustment and repair of gearbox assemblies is performed on a stand, where you can also test the gearbox for noise and check the location and shape of the contact patch on the working surfaces of the teeth, as indicated below.
Checking the contact of the working surface of the teeth of the main gear wheels
For the final check at the bench of the quality of the gearing of the main gears:
- install the adjusted gearbox on the bench and lubricate the working surfaces of the driven gear teeth with a thin layer of lead oxide;
- start the stand, use the stand levers to slow down the rotation of the installed axle shafts so that under loads on the surfaces of the teeth of the driven gear there are traces of contact with the teeth of the driving gear;
- change the direction of rotation of the stand and, braking, get traces of contact on the other side of the teeth of the driven gear, which corresponds to the movement of the car backward.
Meshing is considered normal if on both sides of the driven gear teeth the contact patch is evenly located closer to the narrow end of the tooth, occupying two-thirds of the length and not reaching the top and base of the tooth, as shown in Figure 12, 1.
Cases of improper positioning of the contact patch on the working surface of the tooth are shown in Figure 12 (2, 3, 4, 5).
Disassembly of the assembly is required to adjust the correct position of the pinion with ring replacement.
When assembling, repeat all operations for preloading the roller bearings of the drive gear, for checking the moment of resistance to turning, for preloading the roller bearings of the differential box and for adjusting the lateral backlash of the gearing of the final drive gears.