One of the characteristic signs indicating the need to disassemble and adjust the gearbox is increased noise when the vehicle is moving. Causes of increased noise:
- - displacement of the contact pattern in the engagement of bevel gears as a result of improper adjustment of tapered roller bearings;
- - scoring and chipping of gear teeth, bearing wear, as well as insufficient oil level in the axle housing.
Dismantling of drive axles and their gearboxes
The procedure for dismantling the middle (rear) drive axle is as follows.
Place the vehicle on an inspection pit. Close the wheel valves (only for Ural-4320 and 4420).
Loosen the wheel nuts of the axle being dismantled, remove the protective covers and disconnect the air supply hoses from the wheel valves.
Drain the lubricant from the axle housing.
Raise the rear of the vehicle and place a stand under the rear end of the frame.
Unscrew the wheel nuts and remove the wheels. Install and secure the tool (Fig. 1).
Using the adjusting eccentrics, spread the brake shoes, thereby preventing the axle beam from turning during subsequent disassembly operations.
Remove the driveshaft of the middle (rear) axle, disconnect the hoses and pipelines of the brakes, the sealing system (only for Ural-4320 and 4420), and the tyre inflation system.
Disconnect the upper reaction rod bracket from the axle beam, disconnect and remove the lower reaction rods.
Roll a mounting trolley under the axle and, after removing the axle beam assembly, lower it onto the trolley using the tool.
Disconnect the tool and roll the trolley with the middle (rear) drive axle out from under the vehicle.
When removing the front axle, carry out preparatory work similar to that described above. Additionally, it is necessary to disconnect the pitman arm rod of the steering mechanism from the left steering knuckle arm, and the power steering from the right steering knuckle arm.
Disconnect and remove the lower shock absorber eyes from the brackets.
Using the installed and secured tool, lift the axle and, after unscrewing the nuts of the U-bolts, remove the clamps securing the front springs.
Lower the front drive axle onto the trolley.
Dismantling of gearboxes from the vehicle
The front axle gearbox, unlike the middle (rear) axle gearbox, should be dismantled only after removing the complete axle from the vehicle.
Place the dismantled front axle on supports. Disconnect the steering linkage rod, the brake hoses and the sealing system hoses.
Unscrew the nuts securing the ball joints.
Using a pry bar, remove the steering knuckle assemblies as a whole, using the recesses of the ball joint flanges.
Remove the side cover 35 (see Fig. 2) of the gearbox housing with the oil supply fitting 25 as an assembly and unscrew the bolts and nuts securing the gearbox housing, including the two bolts located inside the housing.
Using a lifting mechanism, remove the gearbox from the axle housing.
The middle (rear) axle gearbox is dismantled directly from the vehicle placed on an inspection pit using a tool; to do this, close the wheel valves, remove the protective covers and disconnect the air supply hoses from the wheel valves.
Drain the lubricant from the axle housing.
Unscrew the bolts securing the hub covers, unscrew the air supply elbows from the axle shafts and remove the hub covers together with the seals and air supply hoses.
Then, using a puller, remove the axle shafts.
Remove the driveshaft of the middle (rear) axle. Disconnect and move aside the upper reaction rod bracket together with the rod, the pipelines and hoses of the brake system and the sealing system.
Remove the side cover of the gearbox with the oil supply fitting as an assembly, unscrew the bolts and nuts securing the gearbox housing, including the two bolts located inside the housing.
Install the tool and remove the gearbox from the axle housing (Fig. 3).
Disassembling the gearbox
The article describes the disassembly of the middle axle gearbox. The disassembly of the front and rear axle gearboxes is carried out in a similar manner.
Bend back the lock plates 23 (see Fig. 2) and lock washers 31, unscrew the bolts 28 and 22.
Remove the differential bearing covers 29.
It should be borne in mind that the holes in the gearbox housing for the differential bearings are machined together with the covers, and before disassembly, the covers and the housing supports on which they are installed should be marked with a centre punch or paint, thereby preventing the covers from being mixed up.
Remove the adjusting nuts 32 and the outer rings of the bearings 33.
Remove the differential 30 as an assembly.
Remove the split pin and unscrew the nut securing the flange 16 of the driving bevel gear shaft, locking the shaft against rotation.
Using a puller, remove the flange.
Unscrew the bolts securing the cover 15 and remove the cover with the sealing collar as an assembly.
Unscrew the bolts securing the bearing cup and remove from the gearbox housing the shaft with the bearing cup, the driving bevel gear, the pack of adjusting shims 11 and the inner ring of the rear bearing 18 as an assembly.
Remove the pack of adjusting shims 11 from the bearing cup. Unscrew the axle sealing plug 13.
Unscrew the bolts securing the cover 9 of the bearing cup of the driving cylindrical gear and remove the cover together with the pack of adjusting shims 6.
Remove the split pins and unscrew the bolts securing the pressure washer 10, remove the washer.
Using a puller or two bolts securing the cover 9, press out the cup 5 together with the tapered bearings 8 and the pack of adjusting shims 4, using the special threaded holes in the cup flange for this purpose.
Secure the packs of adjusting shims to the cover 9 and the bearing cup 5. Through the side window, remove the driven bevel gear assembly from the gearbox housing.
If necessary, press out the outer ring of bearing 2 (Fig. 4), the outer ring of bearing 18 (see Fig. 2) with the rollers from the seats of the gearbox housing and remove the oil supply fitting 25 from the hole of the side gearbox cover.
Disassembling the driven bevel gear assembly
Place the bevel gear on supports and press out the shaft of the driving cylindrical gear. Remove the support washer from it, remove the key from the shaft groove.
Place the driven bevel gear with the bearing inner ring on supports and, using a mandrel and three rods inserted into the gear holes, remove the bearing inner ring with the rollers.
If necessary, use a mandrel to press out the tapered bearings from the cup.
Disassembling the driving bevel gear shaft assembly. Secure the driving gear shaft assembly in a vice.
Remove the split pin and unscrew the nut 1 securing the flange 2 (Fig. 5), using a puller to remove the flange.
Unscrew the bolts securing the cover 4 of the front bearings, remove the cover with the sealing collar as an assembly.
Bend back the washer 14 and unscrew the lock nut 15. Remove the tab washer 14 and the lock washer 13, then unscrew the nut 12.
Place the driving gear shaft assembly on supports and press out the shaft.
Place the bearing cup with the driving gear on supports and, using light blows of a copper hammer on the end, press the bevel gear together with the inner ring of bearing 11 and the adjusting washer 7 out of the cup.
Remove the inner ring of bearing 6 with the rollers from the cup. Remove the adjusting washer from the driving bevel gear shaft.
Using a puller, remove the inner ring of bearing 11 with the rollers.
If there are scores or significant wear on the outer rings of bearings 6 and 11, press the rings out of the cup.
If necessary, use a mandrel to press the sealing collars out of the bearing covers of the driving bevel gear shaft, remove the inner ring 10 of the bearing from the rear journal of the shaft.
Disassembling the differential
Secure the differential in a vice, clamping the rim of the driven cylindrical gear 6 (Fig. 6).
If it is necessary to replace bearings 2, remove them using a puller.
Mark the relative position of the differential cases 3 with a centre punch or paint (the machining of the holes for the differential crosspiece is carried out assembled, and during disassembly it is necessary to preserve the relative arrangement of the cases).
Remove the split pins and unscrew the nuts of the bolts 5 securing the differential cases, remove the bolts.
Place the differential on the plate of the tool (Fig. 7).
Insert a pry bar into the splined hole of the differential side gear and use it to lift the end of the driven cylindrical gear above the plate.
Using sharp hammer blows on the end of the gear ring, press out the differential case.
Remove the side gear 1 (see Fig. 6) with its thrust washer 4.
Remove the crosspiece 7 with the pinions 9 (10 — pinion bush) and the spherical thrust washers 8.
Remove the side gear with its thrust washer from the second differential case.
Press out the second differential case.
Technical condition check
Visually inspect the condition of the axle housing parts.
Operation of the vehicle with the following defects is not allowed:
- - cracks on the axle housing and axle shaft casings; axle beam deflection more than 4 mm;
- - wear and stripping of threads in the holes for the drain and fill plugs, in the holes for the bolts and studs securing the gearbox.
To check the deflection (Fig. 8), place the axle beam on prisms with the journals of the axle shaft casings for the outer hub bearings.
Ensure parallelism of the axle housing parting plane and the control plate plane. Determine dimensions «В» and «С» with an accuracy of 0.5 mm and calculate the deflection value «Н» of the axle beam using the formula:
Н = (В – 60) – (С – 71.25), where «В» is the actual dimension from the control plate plane to the upper part of the axle shaft casing journal; С is the actual dimension from the control plate plane to the parting plane of the axle housing in the middle part.
An axle beam with a deflection of more than 4 mm must be straightened. The diagram for straightening the axle beam is shown in Fig. 9.
When inspecting gearbox parts, it should be borne in mind that cracks and chips in the middle part of the tooth, pitting on an area of more than 25% of the tooth surface are not allowed on the final drive and differential gears.
Gears with chips of the tooth tips along a length of not more than 5 mm from the tooth end are allowed for further work after cleaning the chips.
When scrapping the driving cylindrical gear or one of the bevel gear pair of the final drive, it should be borne in mind that according to the manufacturing technology, these three gears are selected as a set and must be replaced as a set.
Replacement of the driving cylindrical gear or the bevel pair is allowed subject to mandatory verification of the journal size of the driven bevel gear for bearing 2 (see Fig. 10) after its press-fit onto the driving cylindrical gear shaft.
The diameter of the journal for the bearing after pressing the driven bevel gear must be within 90.012–90.035 mm.
The runout relative to the axis of the driving cylindrical gear must not exceed 0.05 mm.
The differential cases are also a set. If one of the cases needs to be replaced, they should also be replaced as a set.
Bearings with chips, cracks, destruction of the cages, as well as spalling, pits, deep scratches and brinelling on the raceways of the rings and rollers should be scrapped.
Replace the sealing collars of the front drive axle shafts and the gearbox bearing covers if there are tears, wear, hardening and cracking of the working edges.
Loosening of the fit of the collars in the cages and bearing covers is not allowed.
When replacing the sealing collar of the front axle shaft, after pressing it into the hole of the axle shaft casing, lock the collar body by centre punching at two points.
On the parts of the constant velocity joints (forks, yokes and disks), run-in (smoothed) scores are allowed, which are the result of mutual run-in of new parts during the running-in period.
Step wear is not allowed on the disks and yokes.
Gearbox assembly and adjustment
Before the general assembly of the gearbox, pre-assemble the units, lubricate the threaded surface of the sealing plug, the mating surfaces of the covers and the gearbox housing with sealing lubricant.
Before installation, lubricate the bearings with transmission oil, and the working edges of the sealing collars with CIATIM-201 lubricant.
Assembly and installation of the driven bevel gear assembly
Using a mandrel, press the inner ring of bearing 2 with the rollers onto the journal of the driven bevel gear 1.
Press the key 3 into the groove of the driving cylindrical gear shaft 5, install the support washer 4 on the shaft and press the driven bevel gear with the inner ring of bearing 2.
In case of scrapping and replacement of one of the gears, assemble the driven bevel gear assembly in the following order.
Press the driven bevel gear 1 onto the gear shaft 5, check the size and runout of the mounting journal for bearing 2.
The diameter of the journal after pressing must be within 90.012–90.035 mm, and the runout relative to the axis of the driving cylindrical gear must not exceed 0.05 mm. If necessary, grind the journal.
After machining the journal, press out the gear 5 and assemble the driven bevel gear assembly in the order described above.
Install and secure the gearbox housing in the tool.
Press the outer ring of bearing 2 into the gearbox housing if it was pressed out during disassembly.
Using a mandrel, press the tapered bearings 8 (see Fig. 2) into the cup 5 and install the cup with the pack of adjusting shims 1 into the hole of the gearbox housing. Install and secure the bearing cup cover 9 with two bolts.
Through the side window of the gearbox housing, install the pre-assembled driven bevel gear assembly.
Unscrew the two bolts securing the cover 9 and remove the cover. Install and secure the pressure washer 10. Cotter pin the bolts securing the pressure washer with wire.
Install and secure the bearing cup cover 9 with the sealing gasket 7 and the pack of adjusting shims 6.
Check and, if necessary, adjust the preload of bearings 8 by selecting the thickness of the pack of adjusting shims 6.
The amount of torque required for smooth rotation of the driven bevel gear assembly should be within 0.09–0.15 kgf·m, which corresponds to a force of 1.75–2.93 kgf applied to the driving cylindrical gear.
When checking the adjustment of the bearing preload, local binding of up to 0.4 kgf·m is allowed.
Measure the torque value during continuous smooth rotation of the driven bevel gear assembly not earlier than after five full revolutions.
Assembly and installation of the driving bevel gear shaft assembly
Before assembling the assembly, determine the required thickness of the adjusting washer 7 (see Fig. 5).
To do this, determine with an accuracy of ±0.05 mm the thickness of the shoulder of the cup 5 (dimension a — Fig. 10) and the distances between the ends of the inner and outer rings of the cup bearings (dimensions b and c).
Determine the required thickness of the adjusting washer using the formula:
S = (a + b + c) – 0.05, where a is the thickness of the cup shoulder; b is the actual dimension from the end of the inner ring of the front bearing of the cup to the end of the outer ring; c is the actual dimension from the end of the inner ring of the rear bearing of the cup to the end of the outer ring.
Having determined the dimension S, select an adjusting washer of the appropriate thickness.
At the manufacturing plant, the preload of the tapered bearings of the assembly is adjusted by selecting an adjusting washer of the required thickness.
The set of adjusting washers produced by the factory consists of 29 pieces with thicknesses of 14.00; 14.05; 14.10; 15.40 mm.
In the absence of a set of adjusting washers and the need to reduce the thickness of the existing adjusting washer, its grinding is allowed.
Using mandrels, press the outer rings of bearings 6 and 11 into the cup 5 (see Fig. 5) until they stop against the shoulder of the cup. Press the inner ring of bearing 11 with the rollers onto the journal of the driving bevel gear 8.
Press the gear 8 onto the shaft 9 and secure the pre-assembled assembly in a vice as shown in Fig. 11.
Install the adjusting washer 7 (see Fig. 5) on the journal of the driving bevel gear; the wider end of the washer should be facing the gear ring of the gear.
Install the bearing cup 5 and, using a mandrel, press the inner ring of bearing 6 with the rollers onto the gear shaft journal until it stops against the adjusting washer.
Screw the nut 12 onto the gear shaft and tighten it.
The nut tightening torque should be within 45–50 kgf·m.
Tap the bearing cup several times with a copper drift and rotate it so that the rollers take the correct position.
Measure the amount of torque required for smooth rotation of the bearing cup of the driving bevel gear.
The torque value should be within 0.06–0.14 kgf·m, which corresponds to a force of 0.75–1.75 kgf applied to the bearing cup.
Measure the torque value during continuous smooth rotation of the bearing cup not earlier than after five full revolutions.
If, when measuring the torque value, the force to turn the cup is less than 0.75 kgf or more than 1.75 kgf, select an adjusting washer whose thickness is respectively smaller or larger by 0.05 mm.
After completing the bearing adjustment, install the lock washer 13 and the tab washer 14.
If, when installing the lock washer, the pin of nut 12 does not fit into the hole of the lock washer, tighten the nut (loosening the nut is not allowed).
If it is not possible to tighten the nut, it is allowed to modify the hole in the washer until it aligns with the pin of the nut. Tighten the lock nut 15 and secure it with the tab washer 14. The lock nut tightening torque should be 45–50 kgf·m.
Install the inner ring of bearing 10 on the journal of the rear end of the driving bevel gear shaft.
Install the pre-assembled and adjusted assembly with the pack of adjusting shims 11 (see Fig. 2) into the gearbox housing. Secure the driving bevel gear cup with bolts.
Using a mandrel, press the outer ring of bearing 18 with the rollers until the rollers stop against the shoulder of the bearing inner ring.
For further adjustment of the gear contact pattern, see the article "Checking and adjusting the axle gearbox of the Ural vehicle".
After completing the adjustment, install the bearing covers with the sealing gaskets and secure them with bolts.
Using a mandrel, press the flanges onto the splined ends of the driving bevel gear shaft, tighten and cotter pin the flange securing nuts.
The cotter pin installed in the hole of the rear end of the driving bevel gear shaft should be located in the direction of the straight edge of the flange (i.e., when installing the flange, it is necessary to orient it relative to the shaft hole for the cotter pin).
The orientation of the flange on the shaft is provided to prevent contact of the cotter pin with the fork of the installed driveshaft.
Assembly and installation of the differential
Before assembly, lubricate the mating surfaces of the side gears, pinions and differential crosspiece with transmission oil.
If, during disassembly of the differential, the inner rings of bearings 2 (see Fig. 6) were removed, place both differential cases 3 on a plate and, using a mandrel, press the bearing rings with the rollers until they stop against the ends of the cases.
Place one of the differential cases on a support. Install the driven cylindrical gear 6 on the differential case, aligning the holes in the case and the gear for the mounting bolts 5.
Install the thrust washer 4 and the side gear 1 into the differential case. Install four pinions 9 with their spherical thrust washers 8 onto the pins of the crosspiece 7. Place the crosspiece with the pinions into the sockets of the differential case.
Place the second side gear with its thrust washer onto the pinions.
Position the thrust washer on the side gear journal so that after installing the second differential case, the tabs of the washer fall into the lubrication holes of the case.
Install the second differential case, aligning the marks made during disassembly.
Insert the bolts 5 into the holes of the differential cases and the hub of the driven cylindrical gear, screw the nuts onto the bolts. Install the bolts from the side of the larger recess of the gear hub.
Secure the differential in a vice, clamping the rim of the driven cylindrical gear. Tighten the nuts of the bolts securing the differential cases.
Check the correct assembly of the differential. The rotation of the gears in the assembled differential should be free when turning the side gear with a splined mandrel.
After completing the check, cotter pin the nuts of the bolts securing the differential cases.
Install the assembled differential on the supports of the gearbox housing; the rim of the driven cylindrical gear should take a position symmetrical relative to the rim of the driving cylindrical gear, and the heads of the bolts securing the differential cases should be directed towards the driven bevel gear.
Install the outer rings of the bearings and place the differential bearing covers in accordance with the marks made during disassembly. Tighten the bolts securing the covers. The bolt tightening torque is 25 kgf·m.
Screw in the adjusting nuts until the ends of the nuts touch the outer rings of the bearings.
Adjust the differential bearings. To do this, install an indicator bracket and, by tightening one of the adjusting nuts, achieve an increase in the distance between the differential bearing covers of 0.15–0.25 mm. At the same time, to correctly position the bearing rollers, rotate the differential several times by the driven cylindrical gear.
After completing the adjustment, install the lock plates 27 (see Fig. 2) into the grooves of the adjusting nuts and secure them with bolts 28.
Lock the corresponding bolts by bending the lock plates 23 and the lock washers 31. Screw the axle sealing plug into the hole of the gearbox housing.
Check the operation of the assembled gearbox by turning it by hand by the flange of the driving gear shaft. The gears should rotate without noticeable binding.
Gearbox testing
Run in the assembled drive axle gearbox on a special stand; in the absence of a stand, conduct the test by a control run on the vehicle.
Test the gearbox on the stand with reversing and light braking at a speed of rotation of the driving bevel gear shaft of 1000 rpm.
To avoid scoring and binding, the test duration should not exceed 0.5 minutes.
Evidence of correct assembly and adjustment of the gearbox is the absence of knocks, increased gear noise and the presence of a contact pattern on both sides of the tooth of the driven bevel gear.
If there is increased noise or knocking, disassemble the gearbox. Check the bearing adjustment, the position of the contact pattern and, if necessary, repeat the gearbox adjustment.
Testing of drive axles. After assembly, run in the drive axle on the stand without load.
Run in at a speed of 1200–1500 rpm in forward and reverse for one minute, and at a speed of 2400–2600 rpm in forward for 3 minutes.
Before the test, pour 4 litres of industrial oil I-20A into the axle housing. During running in, check the smoothness and noise level of the gearbox, as well as the operation of the front axle joints by turning the hubs in both directions.
After running in, drain the oil from the axle housing.
Check the drive axles of Ural-4320, -4420 vehicles for tightness of the air supply collars, as well as the connections of the gearbox, the axle beam and the steering knuckle assemblies.
Check the tightness of the air supply collars for 10 minutes under an air pressure of 3.2 kgf/cm².
Plug the threaded holes of the axle shaft casings (or the fittings of the steering axles of the front axle) for the ends of the flexible hoses of the tyre inflation system.
Supply air through the air supply hoses.
Air leakage during the check is not allowed.
Check the tightness of the connections of the middle (rear) drive axle by supplying air through the hole in the gearbox housing under the plug of the sealing system.
When testing the front drive axle, check the tightness of the connections of the gearbox and the steering knuckle assemblies by simultaneously supplying air through the holes in the steering knuckle housings and the gearbox housing under the fittings and the plug of the sealing system.
The air pressure during testing is 0.35 kgf/cm²; the permissible air pressure drop is not more than 0.1 kgf/cm² within 1 minute.
During the tests, perform several revolutions of the driving bevel gear shaft, and also turn both steering knuckle housings of the front axle from one extreme position to the other.
Install the gearbox (axle) on the vehicle in the reverse order of dismantling. After tightening the bolts and nuts of the gearbox housing, cotter pin the two bolts located inside the housing with wire.
When installing the side cover of the gearbox housing, coat both sides of the sealing gasket 34 (see Fig. 2) with a thin layer of oil paint.
After securing the side cover of the front axle gearbox housing, lock the two screws securing the cover by centre punching at two points.
