Disassembling the gearbox shafts is necessary to replace the shaft parts.
Removing the gearbox is discussed in the article - "How to replace the gearbox of the Niva Chevrolet"
Disassembling the gearbox is discussed in the article - "Repairing the gearbox of the VAZ-2123 car"
Disassembling the gearbox input shaft
Use pliers to open the retaining ring and remove it.
Remove the spring washer.
Lean the end of the outer bearing ring on the jaws vice.
With a plastic-headed hammer, strike the end of the input shaft and press out the bearing
Use pliers to spread the mounting ring and remove it.
After moving the synchronizer locking ring, use pliers to loosen the retaining ring and remove it.
Remove the locking ring and synchronizer spring
The synchronizer locking rings of other gears are removed in the same way
Assemble in reverse sequences
Disassembling the secondary shaft of the gearbox
Remove the bushing and the 1st gear assembly with the locking ring from the rear side of the shaft.
Remove the bushing from the gear.
Remove the synchronizer sleeve of the first and second gears.
Removing the synchronizer hub.
Removing the 2nd gear assembly with the locking ring
From the front end of the secondary shaft, remove the synchronizer clutch of the "III" and "IV" gears
Having clamped the secondary shaft in a vice with soft metal jaw pads, remove the retaining ring with pliers.
Remove the spring washer (it is installed with the convex side to the front end of the shaft).
Remove the synchronizer hub of the "III" and "IV" gears
Remove the gear "III" of the transmission together with the synchronizer locking ring.
Assemble in the reverse order