When removing the gearbox, it is necessary to unscrew the bolts securing the cab floor cover, remove it and unscrew the driveshaft mounting flange
Unscrew the bolts securing the PSU to the bracket, disconnect the pusher from the clutch fork lever and, without disconnecting the pipelines, secure the PSU to the car so as not to damage the pipelines.
Remove the housing with the gear shift lever.
Disconnect the intermediate support bracket from the frame cross member and lower the driveshaft, disconnect the speedometer shaft.
Unscrew the nuts of the studs securing the gearbox to the clutch housing using a spanner.
Disconnect the gearbox from the clutch housing and remove it using a jack-trolley with a special puller 32P-1270 (Fig. 5-2).
Having removed the gearbox from the car, you need to replace the housing with the gearbox control lever.
Before disassembling, it is necessary to drain the oil, remove the plug from the drain hole, then clean and rinse the outside of the gearbox.
Using the suspension (Fig. 5-3), hook the box, lift it with a lift and install it on the device (Fig. 5-4) for disassembling and assembling gearboxes.
Installation of the gearbox on the bus is carried out in the reverse order of its removal.
Disassembling the gearbox
To remove and disassemble the gear shift lever tip housing, unscrew the first gear switch fuse cottages and reverse
Unscrew the four crankcase mounting bolts, remove the crankcase with the lever assembly and the crankcase gasket.
Unscrew the nut from the tip, remove the lever and remove the key.
Secure the lever tip housing in a vice, pointing the tip down.
Unscrew nut 3 (Fig. 5-5) securing the intermediate lever axle, while holding the axle head, remove the spring washer and axle 4 with the intermediate lever.
Then remove the axle from the lever hole and the fuse.
Remove spring 5 from the crankcase, remove lever support 6, remove lever assembly 10 and lever retainer 7.
Removing and disassembling the gear shift mechanism
Unscrew the bolts securing the box cover, remove the cover assembly with the gear shift mechanism, remove the cover gasket.
If the gasket is stuck, you must carefully separate it using a screwdriver or other tool.
The gearbox shift mechanism is disassembled in a device (Fig. 5-6), in which the cover is secured in a position convenient for disassembly.
If there is no device, the cover can be disassembled by securing the cover in a vice.
Disassembly of the gear shift mechanism must be carried out in the following order.
Unsplit the locking bolts securing the forks and safety heads on rods 9, 10, and 11 (Fig. 5-7), unscrew the locking screws securing the forks and the bolts securing the rod heads.
Using a wrench, move one gear shift rod and press the plug out of the socket.
Moving the rod, remove the plug and, holding the locking balls with your hand, remove the rod with the other hand. In a similar way, remove the other two gear shift rods.
Removing and disassembling the input shaft
Disconnect the release spring from the clutch release bearing clutch, remove the clutch with the bearing assembly.
Unscrew the four bolts securing the front input shaft bearing cover and remove the cover with the gasket.
To remove the input shaft from the crankcase socket, you need to press out the ball bearing using a puller 40P-5019 (Fig. 5-8) and remove the shaft and bearing assembly.
(Usually the input shaft is easily pressed without a puller, using two screwdrivers)
Remove the locking rings (Fig. 5-9) and press the bearing using a tool.
Removing and disassembling the secondary shaft
Having locked the first gear gear with a wrench, unscrew the nut of the secondary shaft flange and press the flange.
Unscrew the bolts securing the secondary shaft cover and remove the cover with the gasket.
Remove the speedometer drive gear from the end of the secondary shaft.
Press the secondary shaft bearing together with the shaft from the housing housing using a mandrel and a hammer.
Use a tool to compress the secondary shaft bearing (Fig. 5-10), remove the secondary shaft assembly with gears and synchronizers from the box housing (Fig. 5-11, a).
Remove synchronizer 1 for fourth and fifth gears and gear 12 for first gear from the shaft.
Remove using two screwdrivers (locking ring 2 securing the fourth gear gear.
Remove thrust washer 3 together with gear 4 of the fourth gear and steel bushing 5 together with the stopper, thrust washer 6 and gear 7 of the third gear, synchronizer 8 of the second and third gears.
Using two screwdrivers, remove the locking ring securing the second gear.
Remove the thrust washer and second gear. Synchronizers should not be disassembled unless necessary.
Removing and disassembling the intermediate shaft and reverse gear block
Unscrew the bolt securing the stopper of the reverse gear block axis, remove the stopper, and remove the block axis from the crankcase.
To press out the axis 55 of the reverse gear block, use a puller model I.803.20.00 (Fig. 5-13).
Unscrew the four bolts securing the rear bearing cover of the intermediate shaft, remove the cover with the gasket, bend the thin edge of the nut, lock the intermediate shaft gear with a wrench and unscrew the nut securing the rear bearing.
Press the rear bearing together with the intermediate shaft out of the crankcase housing, move the shaft with gears along the axis towards the bearing.
Press the rear intermediate shaft bearing using a puller.
The method of pressing this bearing from the shaft is the same as pressing the bearing from the secondary shaft.
Remove the intermediate shaft and gear assembly from the crankcase manually.
Remove the outer race of the intermediate shaft bearing from the crankcase housing.
If necessary, use a mandrel to knock out the plug covering the front bearing and remove the retaining ring.
To disassemble the intermediate shaft, press the inner ring of the bearing with the rollers, remove the lock ring 1 (Fig. 5-15), press all the gears off the shaft and remove the keys from the grooves.
Gears can be pressed using a device or using pads on a press. The last two gears 6 for reverse gear and 7 for second gear must be pressed together.
Checking gearbox parts
Gearbox housing cast from gray cast iron grade SCh24 GOST 1412-85.
After removing the associated parts from the gearbox housing, you must carefully check the condition of the mating surfaces, the absence of cracks and the amount of wear of the bearing holes
Cracks and holes in the gearbox housing are a defective sign.
If the bearing holes are worn beyond the permissible dimensions, the gearbox housing must be replaced.
Damage to the threads in the crankcase holes is allowed within no more than two threads.
The runout of the front and rear ends of the crankcase relative to the common axis of the holes for the secondary shaft bearing is allowed within 0.08-0.15 mm.
The diameters of the holes in the crankcase of the intermediate and secondary shafts and the deviation from the common plane passing through them should not exceed 0.07-0.12 mm over the entire length of the crankcase.
The non-flatness of the remaining mating surfaces of the gearbox housing should be within 0.15-0.30 mm.
Input shaft with ring gear, constant mesh gears and spline hole.
The primary shaft is made of steel 25KhGM, the depth of the nitro-carburized layer is 0.6...0.8 mm, the hardness of the surface layer is NRSe 61-66, the hardness of the core is NVSe37-46.
If the journals and shaft splines are worn beyond what is acceptable without repair, the input shaft should be replaced.
Worn shaft journals can be repaired by chrome plating and then processed to the nominal dimensions.
The runout of the inner hole of the new input shaft relative to the bearing journals is allowed no more than 0.02 mm.
If there is a bend or twist, the shaft must be replaced.
The input shaft gear teeth must not be cracked.
Minor nicks, burrs and chips at the ends of the teeth should be cleaned.
The secondary shaft is made of steel 25KhGM, the depth of nitrocarburization is 0.8-1.1 mm, the hardness of the surface layer is НВСе 61-66, the hardness of the core is НРСе 37-46.
The runout of the secondary shaft journals relative to the axis is allowed no more than 0.05 mm.
The use of journals with a crumbled cemented layer due to fatigue is not allowed.
Secondary shaft gears. The runout of the ends of the gearbox gears is allowed no more than 0.05 mm.
If there are cracks on the gears, large wear on the teeth and splines, the gears should be replaced. Minor chips on the ends of the teeth should be cleaned. Chips on the working surface are not allowed.
Synchronizer carriages are made of steel 25ХГТ, nitrocarburization depth is 0.7-0.9 mm, surface layer hardness НРСе 61-66, core hardness НЯСе 37-46.
Cone rings - brass, stamped.
If there is wear on parts and loss of spring elasticity, the synchronizer should be replaced as an assembly. For the new synchronizer, axial and radial runout of the carriage of up to 0.1 mm is allowed.
Intermediate shaft. The intermediate shaft is made of steel 25KhGM, the depth of nitrocarburization is 0.8-1.1 mm, the hardness of the surface layer is NYSe 58..61, the hardness of the core is NRSe 35-45.
The runout of the intermediate shaft journals relative to the axis is allowed no more than 0.04 mm.
Faulty shaft journals can be repaired by chrome plating and then processed to the nominal dimensions.
Intermediate shaft gears
The requirements for repairing the intermediate shaft gears are similar to the requirements for the secondary shaft gears.
The gear block and the axis of the reverse gear block. The gear block is made of steel 25KhGM, the depth of nitrocarburization is 0.5-0.8 mm, the hardness of the surface layer is NRSe 58-61, the hardness of the core is NRSe 37-46.
The requirements for repairing the gear block are similar to the requirements for repairing the secondary and intermediate shaft gears.
Gearbox housing cover with gear shift mechanism
Cracks and chips are not allowed on the gearbox cover.
If the holes in the cover for the gear shift rods are worn, the cover should be replaced or repaired by installing bushings.
The bent of the gear shift rods is allowed no more than 0.1 mm. Bent rods can be repaired by straightening.
Gear shift rods worn beyond the permissible limits should be replaced or restored by chrome plating and subsequent processing.
Wear of the grooves in the rods for the locking balls is allowed such that the clearance between the profile template and the groove does not exceed 0.6 mm.
If the specified tolerance is exceeded, the rods should be replaced.
If there are cracks or breaks on the forks, heads and gear shift lever, they should be replaced.
Bent forks and shift levers can be repaired by straightening.
If the shift fork tabs are worn beyond the permissible fork size, the fork should be replaced.
If the groove in the forks and the head for the gear shift lever is worn out, or the holes in the forks and the head for the gear shift rod are worn out, they should be replaced.
If the groove for the gear shift lever retainer is worn, the lever should be replaced.