Wash gear parts thoroughly before inspecting.

This will make it easier to identify wear and damage to parts

Check for damage on the gear teeth of the final drive and check that the contact spots on the working surfaces of the teeth are correctly positioned

In case of unacceptable wear, replace the parts with new ones; if the engagement is wrong, find the reason.

In spare parts, the driving and driven gears are supplied in 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 with fine-grained sandpaper, and in case of serious damage, replace the parts with new ones.

Check the surfaces of the journals of the gears of the axle shafts and their mounting holes in the differential box, the condition of the holes in the box for the axis of the satellites.

Remove any damage found, as in the previous operation, if necessary, replace worn or damaged parts.

Inspect the surfaces of the bearing washers of the gears of the axle shafts, repair even minor damage. When replacing washers, select new ones according to their thickness.

Inspect the roller bearings of the drive gear and differential box; they must be wear-free, with smooth working surfaces.

Replace bearings at the slightest doubt about their performance, poor bearing condition can cause noise and seizing teeth.

Check for deformations or cracks on the crankcase and on the differential box, if necessary, replace them with new ones.

Reducer assembly

Reliable operation of the gearbox is ensured by strict adherence to the following assembly and adjustment techniques.

Details of the rear axle gearbox: 1 - drive gear flange; 2 - stuffing box; 3 - oil deflector; 4 - front bearing; 5 - rear bearing; 6 - adjusting ring of the drive gear; 7 - support washer of the axle gear; 8 - axle gear; 9 - satellite; 10 - axis of the satellites; 11 - driven gear; 12 - differential box; 13 - differential box bearing; 14 - adjusting nut; 15 - a bolt of fastening of a locking plate; 16 - locking plate; 17- locking plate; 18 - a bolt of fastening of a driven gear; 19 - drive gear; 20 - cover fastening bolt; 21 - spring washer; 22 - gasket; 23 - gearbox mounting bolt; 24 - gearbox housing, 25 - spacer sleeve; 26 - flat washer; 27 - pinion flange nut

Reducer details are shown in Figure 1.

Differential assembly

Lubricate with gear oil and install the axle gears with support washers and satellites through the windows into the differential box.

Rotate the planetary gears and axle gears so that the axis of rotation is aligned with the axis of the hole in the box, then insert the planetary axle.

Check the axial clearance of each axle gear: it should be 0-0.10 mm, and the moment of resistance to rotation of the differential gears should not exceed 14.7 Nm (1.5 kgcm).

If the gap is increased, which is a sign of wear of the differential parts, replace the support washers of the gears of the axle shafts with others of greater thickness.

If the specified clearance cannot be obtained even with the thickest washer, replace the gears with new ones due to excessive wear.

Attach the driven gear to the differential case.

Using drift A.70152, press the inner races of 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 the mandrel A.70184 and tool A.95690 with indicator.

Perform operations in the following order.

Installing the pinion rear bearing outer race with a mandrel: 1 - A70.171 mandrel

Having fixed the gearbox housing on the stand, press the outer rings of the front and rear bearings of the drive gear into the housing sockets, using mandrels for this: for the front bearing A.70185, and for the rear bearing - A.70171 (Figure 2).

Determining the thickness of the drive gear adjusting ring: 1 - indicator, 2 - tool A95690, 3 - rear drive gear bearing, 4 - mandrel A.70184

On mandrel A.70184, which imitates the drive gear, use mandrel A.70152 to install the inner ring of the rear bearing and insert the mandrel into the neck of the gearbox housing (Figure 3)

Install the inner ring of the front bearing, the drive gear flange and, turning the mandrel to properly install the bearing rollers, tighten the nut to a torque of 7.85-9.8 Nm (0.8-1 kgcm).

Fix fixture A.95690 on the end of mandrel 4 and adjust the indicator, which has divisions of 0.01 mm, to the zero position by placing its leg on the same end of mandrel A.70184.

Then move indicator 1 so that its foot rests on the seating surface of the differential box bearing.

Scheme for taking measurements to determine the thickness of the drive gear adjusting ring: 1 - mandrel A70184, 2 - fixture A95690 with indicator, a1 and a2 - distance from the end of the mandrel to the differential bearing journals

Turning the mandrel 4 with the indicator left and right, set it to a position where the indicator arrow marks the minimum value “a 1” (Figure 4) and write it down.

Repeat this operation on the seat of the second bearing and determine the value "a2".

Determine the thickness "S" of the drive gear adjusting ring, 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 drive gear from the nominal position translated in mm.
Final gears: 1 - driven gear, 2 - serial number, 3 - correction in hundredths of a millimeter to the nominal position, 4 - drive gear

The deviation value 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 value "b" and its unit.


Let's assume that the value "a" set using the indicator is 2.91 mm (the value "a" is always positive), and the deviation "-14" is put on the drive gear after the serial number.

To get the value of "b" in millimeters, you need to multiply the indicated value by 0.01 mm.

b = -14 0.01 = -0.14 mm

Determine the thickness of the shim for the pinion in millimeters.

S = a - b = 2.91 - (-0.14) = 2.91 + 0.14 = 3.05 mm

In this case, install a 3.05 mm thick adjusting ring.

Installing the rear bearing inner race to the drive gear: 1 - roller bearing ring, 2 - A70152 drift, 3 - adjusting ring, 4 - drive gear

Put an adjusting ring of the required thickness on the drive gear and press on the inner ring of the rear bearing removed from the mandrel A.70184 using drift A.70152 (Figure 6).

Put on the spacer.

When repairing the rear axle gearbox, a new spacer must be installed if the gearbox housing, final drive gears or drive gear bearings have been replaced.

If the specified parts remain the same, then the spacer sleeve can still be used.

Insert the drive gear into the gear housing and install the front bearing inner race, oil slinger, oil seal, drive gear flange and washer onto it.

Screw a nut onto the end of the gear and tighten it, locking the flange of the drive gear.

Adjusting the drive gear bearings

Dynamometer 02.7812.9501: 1 - moveable pointer, 2 - torque limit pointer, 3 - housing, 4 - handle, 5 - rod with a tip inserted into the adapter sleeve

To limit the axial displacements of the drive gear under working loads, it is very important to create a preload in its bearings within the specified limits.

The preload is controlled by a dynamometer 02.7812.9501 (Figure 7), which measures the moment of resistance to turning the drive gear.

The torque of resistance to rotation determines 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 30 km and more.

It is necessary to tighten the flange nut periodically by checking with a dynamometer the moment of resistance of the bearings to turning the drive gear.

In this case, the torque on the nut can be in the range of 118–255 Nm (12–26 kgf m).

Checking the preload of the drive gear bearings: 1 - dynamometer 02.7812.9501, 2 - crankcase, 3 - adapter sleeve

To check the moment of resistance, put a dynamometer on the adapter sleeve 3 (Figure 8), set the pointer 2 (see Figure 7) of the torque limit to a division of the scale corresponding to 196 N cm (20 kgf cm), and use the handle 4 to make several revolutions clockwise.

During the rotation of the drive gear, the movable pointer 1 must not go beyond the pointer 2 and must show at least 157 N cm (16 kgf cm).

If the moment of resistance to rotation is less than 157 N cm (16 kgf cm), and for bearings after 30 km of run 39.2 N cm (4 kgf cm), then tighten the drive gear flange nut (without exceeding the specified torque tightening) and check again the moment of resistance to turning the drive gear.

If the torque resistance is greater than 196 Ncm (20 kgfcm) and for worn-in bearings is 58.8 Ncm (6 kgfcm), indicating excessive bearing preload, replace the spacer with a new one, because it was deformed from excessive load to a size that did not allow for correct adjustment.

After replacing the spacer sleeve, repeat assembly with appropriate adjustments and checks.

Installing the differential box

Install the pre-assembled differential case with bearing outer races into the crankcase.

Checking the differential box bearing preload with tool A.95688/R: 1 - tool screw; 2 - key A.55085; 3 - driven gear; 4 - adjusting nut; 5 - intermediate lever; 6 - fastening screw; 7 - indicator bracket; 8 - bracket mounting screw; 9 - indicator for checking bearing preload

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.

Preload bearings of the differential box and adjustment of the backlash in the meshing of the final drive gears

These operations are performed simultaneously with the aid of the A.95688/R tool and the A.55085 key.

Fix the fixture to the gearbox housing with screws 1 and 6, screwing them into the holes for the bolts for fastening the locking plates of the adjusting nuts.

Move bracket 7 along the tool guide until lever 5 touches the outer side surface of the cover and tighten screw 8.

Loosen screws 1 and 3 (figure 10) and install bracket 4 so that the indicator leg 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 backlash between the teeth of the drive and driven gears within 0.08–0.13 mm.

The clearance is checked by indicator 2 while rocking gear 6. 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.

Checking the side clearance in the meshing of the gears of the final drive with the aid of A.95688/R: 1 - bracket fastening screw; 2 - indicator for wire lateral clearance rki in the meshing of gears; 3 - screw for fastening the indicator rod; 4 - indicator bracket; 5 - fastening screw; 6 - driven gear

Sequentially and evenly tighten the two adjusting nuts of the bearings, while the differential bearing caps diverge and, therefore, the distance "D" (figure 11) increases by 0.14–0.18 mm.

After setting the exact preload of the differential case bearings, finally check the backlash in the meshing of the final drive gears, which should not change.

If the gap in the meshing of the gears is more than 0.08–0.13 mm, then move the driven gear closer to the drive gear or move it away if the gap is smaller.

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.

To accurately perform this operation, watch indicator 9 (see figure 9), which shows the previously set bearing preload.

After tightening one of the nuts, the indicator reading will change, as the discrepancy "D" (see figure 11) of the covers increases and the preload of the bearings increases.

Therefore, loosen the other nut until the indicator arrow returns to its original position

Diagram for checking the preload of differential case bearings: D is the distance between two differential bearing caps; 1, 2 - adjusting nuts

After moving the driven gear, on the indicator 9 (see Figure 9), check the amount of backlash. If the gap is not correct, repeat the adjustment.

Remove tool A.95688/R, install the locking plates of the adjusting nuts and secure them with bolts and spring washers.

Two types of locking plates are available for spare parts: with one or two tabs, depending on the position of the nut slot.

Adjustment and repair of the gearbox units is carried out on the 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 gear teeth of the final drive

For the final check on the stand of the quality of the main gear engagement:

  • - install the adjusted gearbox on the stand and lubricate the working surfaces of the teeth of the driven gear with a thin layer of lead oxide;
  • - start the stand, use the levers of the stand to slow down the rotation of the installed semi-axes so that under loads on the surfaces of the teeth of the driven gear there are traces of contact with the teeth of the drive gear;
  • - change the direction of rotation of the stand and, while braking, get contact marks on the other side of the teeth of the driven gear, which corresponds to the movement of the car back.

Engagement is considered normal if on both sides of the teeth of the driven gear the contact patch is evenly located closer to the narrow end of the tooth, occupying two-thirds of the length and not extending to the top and bottom of the tooth, as shown in Figure 12

Location of the contact patch in the main gear engagement: A - forward side; B - reverse side; 1 - the correct location of the contact patch; 2 - the contact spot is located at the top of the tooth - to correct, move the drive gear to the driven gear; 3 - the contact spot is located at the base of the tooth - to correct, move the drive gear away from the driven gear; 4 - the contact patch is located at the narrow end of the tooth - to correct, move the driven gear away from the drive; 5 - the contact patch is at the wide end of the tooth - to correct it, move the driven gear to the drive gear.

Cases of incorrect location of the contact patch on the working surface of the tooth are shown in Figure 12 (2, 3, 4, 5).

To adjust the correct position of the drive gear with the replacement of the ring, disassembly of the assembly is necessary.

When reassembling, repeat all operations for preloading the pinion roller bearings, checking the torque resistance, preloading the differential case roller bearings, and adjusting the final drive gear engagement backlash.