Disassembling the gearbox
Clean the gearbox, drain the oil from the gearbox sump and install it on a stand for disassembly.
Loosen the mounting bolts and remove the rear cover of the gearbox, remove the adjusting ring of the rear bearing of the secondary hall and the sealing gasket.
Carefully move the fork rod of the third and fourth gears in the direction of the third gear until the lock is released. Remove the lock, then set the fork rod to the neutral position.
Warning. Pull the fork rod of the III and IV gears only to the required extent, so that the synchronizer crackers do not fall out. If they fall out, the fork rod will not be able to be set to the neutral position without removing the nut from the end of the secondary shaft.
Engage reverse gear and 1st gear to lock the primary and secondary shafts, and loosen the nut from the end of the secondary shaft.
Install the mounting cross member onto the clutch housing.
Screw the bolt into the primary shaft end until it stops.
Remove the retaining ring and thrust washer from the input shaft
Press the primary shaft ball bearing out of the clutch housing socket.
Remove the gearbox housing together with the shafts and knock out the mounting pins.
Clamp the gearbox housing with shafts in a vice with soft metal pads.
Knock out the spring pin from the shift fork of the third and fourth gears, holding the fork rod with a hammer so as not to damage the hole for the fork rod in the partition.
Pull out the fork rod of the III and IV gears so that the fork of the III and IV gears can be removed. Then move the fork rod to the neutral position.
Remove the primary shaft from the gearbox housing.
Knock out the axle and remove the reverse intermediate gear.
Knock out the spring pin from the 1st and 2nd gear shift fork rod linkage using a punch and remove the linkage from the fork rod.
Press the secondary shaft out of the gearbox housing.
Warning: When pressing the secondary shaft, make sure that the fork of the first and second gears does not lock. If it does, release it by lightly hitting the fork.
Remove the differential output shaft mounting bolts while holding the shaft with a mandrel.
Loosen the differential box cover mounting bolts.
Remove the differential cover using two pry bars.
Remove the differential.
Details of the four-speed gearbox housing: 1 — clutch housing; 2 - plug; 3 — breather; 4 - filler plug; 5 - drain plug; 6 — mounting pin; 7, 12 — bushing; 8 — lower clutch housing cover; 9 — gearbox housing; 10 - washer; 11 — lower cover bolt; 13 - cork; 14 — gearbox cover; 15 - gasket; 16 - cork; 17 — gearbox cover gasket; 18 — secondary shaft bearing; 19 — ring; 21 - hairpin; 22 — differential box cover stud; 23 - washer; 24 - nut; 25 — pin; 26 - hairpin.
Four-speed gearbox details: 1 — primary shaft; 2 — third gear pinion; 3 — 4th gear pinion; 4 — clip; 5 — oil seal; 6, 15, 24, 30 - needle bearings; 7, 16 — bearings; 8 - adjusting washer; 9, 36 - pins; 10, 18 — locking ring; 11 — sliding clutch of synchronizer III and IV gears; 12, 27 — synchronizer springs; 13, 29 - crackers; 14, 26 — synchronizer locking rings; 17 - lock washer; 19 — secondary shaft; 20, 41 - bearing with locking pin; 21 — 4th gear pinion; 22 — third gear pinion; 23 - adjusting ring; 25 — 2nd gear pinion; 31 — 1st gear pinion; 32 - adjusting ring; 33 — thrust ring; 34 — secondary shaft rear bearing; 35, 40 - nuts; 37 — reverse intermediate gear axle; 38 — reverse intermediate gear; 39 — Reverse axle bushing; 41 — bearing retaining stud; 42 — speedometer drive; 43 — speedometer drive gear; 44, 45 — differential box cover with gasket; 46 — ring; 47 — speedometer drive pinion; 48 - adjusting ring; 49 — outer ring of differential box bearing; 52 — inner bearing ring; 51 — differential box; 52 — satellite axis; 53 — driven gear of the main transmission; 54 — oil seal; 55 — differential output shaft; 56 - thrust washers; 57 - satellites; 58 — differential gears.
(Information obtained from this resource AUDImanual)