The final drive can be adjusted or repaired without removing the rear axle from the vehicle.
The preload of the final drive bearings, the lateral clearance in the engagement and the contact patch are adjusted at the factory and, as a rule, they do not require adjustment during operation.
Their adjustment is only necessary after the axle has been overhauled and parts have been replaced, as well as in the case of significant wear of the bearings.
The lateral clearance in the engagement of the final drive, which has increased due to wear of the teeth, is not reduced by adjustment, since this leads to a disruption of the engagement and, as a consequence, to increased wear of the teeth, increased noise or breakage of the teeth. Increased clearances in bearings are eliminated without disturbing the relative position of the gears.
The need to adjust the bearings can be determined by the presence of axial movement of the drive gear, which indicates the appearance of clearance in the bearings.
This clearance is determined with the cardan shaft disconnected using an indicator with a division value of no more than 0.01 mm when moving the flange in the axial direction.
The indicator foot should rest against the end of the flange parallel to the axis of the drive gear.
A clearance in the bearings is not allowed.
If there is a clearance, before proceeding with the adjustment of the bearings, it is necessary to check the tightening of the drive gear flange fastening nut with a torque of 400-550 Nm, since the clearance may appear due to loosening of the tightening. There is no need to loosen the nut, the extrusion is cut off when the nut is turned.
If the gap is eliminated after tightening, lock the nut by pressing (without tearing) its edge into the groove on the gear shaft.
If the turn was insignificant and the deformed part of the nut coincides with the shaft groove, then the nut should be replaced with a new one or one removed from another bridge.
If tightening fails to eliminate the gap, then record its value and adjust the bearing preload.
The wear of the main gear components can also be judged by the angular clearance measured on the flange of the drive gear.
To measure, put a mark on the edge of the flange mud deflector, turn the flange to the left until it stops and make a line on the bearing cup that coincides with the mark on the mud deflector.
Turn the flange all the way to the right and make a second mark on the bearing cup.
Measure the distance between the marks.
If it exceeds 13 mm, this indicates excessive wear of the teeth of the drive and driven gears of the main transmission, differential gears or splines of the half-axle gears and half-axles.
You can see the adjustment of the gearbox in the article - Adjustment of the main transmission ZIL-5301