Checking the tightening of the drive gear nut of the VAZ and Lada Niva gearbox
First of all, we clean the gearbox neck, drive gear flanges and cardan joint from dirt. To get to the nut (S24 M16x1.5), you need to disconnect the flanges and move the propeller shaft to the side. It is balanced separately from the drive gear with a flange and still mark the relative position of the flanges with paint or a punch.
The nuts (S13, M8) of flange bolts with special heads that are to be unscrewed require very careful attention. Do not use a spanner or socket here. A regular open-end wrench “13” (S13) must be new or, in any case, tightly cover the edges of the nut. You can make a “dense” S13 key from an S12 key.
The fact is that the nuts of the flange bolts can be tightened to a torque of up to 3.5 kgf (with a wrench arm of 150 mm - a force of 21 kgf). If we take into account that the coefficient of static friction is always greater than the coefficient of sliding friction, the force on the key will be considerable. At the slightest “slack” in the key, the hexagon of the nut will quickly be crushed (“licked”). When rounding the corners of the nut faces, as a rule, a hammer and chisel are used. If there is nothing to replace the nut after this, you have to machine its edges for an S12 hexagon.
We begin to unscrew the nut that is in a comfortable position (then we turn the driveshaft), not forgetting about the bolt. The fact is that the conical head of the bolt has a flat, while the bolt rests against a special milling of the flange and is kept from turning. There is no point in rotating the nut and rotating the bolt along with it, thereby crushing the edges. It is better to jam the bolt head with a screwdriver in a timely manner.
When all the nuts are unscrewed, the bolts are removed, and when removing the propeller shaft flange, oil is found between the flanges - this is the first sign that the shank nut has been unscrewed and hot oil has easily penetrated into the interflange space through the unclamped ends of the parts and the spline joint.
Installation of the drive gear of the VAZ and Lada Niva gearbox.
The second sign of a loose nut is the presence of axial play in the drive gear. Grasp the flange with both hands and move it back and forth (the car is on a stand, with stops under the wheels). The drive gear nut may be unscrewed a full turn or more (1 turn - axial movement - is equal to the thread pitch, i.e. 1.5 mm). Here we are no longer talking about preload and you are lucky that the gearbox is still working.
Universal wrench for flanges and hubs
If tightening the nut is a “one-time event” and there is no special wrench, you can get by with two M8 bolts and a wrench (metal rod). The bolts are inserted into the flange holes, and the knob is placed between the bolts in front of the flange. If the knob is placed behind the flange, you may accidentally press on the dirt deflector, after which it will need to be secured to the flange.
After unscrewing the nut, it is necessary to remove oil from the threads of the nut and the gear shank, which will significantly increase the coefficient of friction and, consequently, the moment of resistance to unscrewing the nut. It is better to install a new nut, since the thread of the gear shank is imprinted in the nylon of the insert, which reduces the resistance to self-loosening of the nut.
The nut must be tightened, as noted above, with a torque of 12-26 kgcm; tightening is controlled by the moment of resistance to rotation of the drive gear - 4-6 kgcm. Since this moment cannot be measured “in its pure form” (the gearbox has not been removed), we measure it with the nut loosened and, adding 4-6 kgcm to the resulting value, we obtain a controlled moment of total resistance.
The easiest way to measure torque is with a spring scale (steelyard). So, if the moment of resistance is 4-6 kgf, and the hook of the scale is hooked onto the flange hole, then the force on the scale should be 1.1-1.7 kgf. Let us remember that the moment of resistance to rotation is measured, and not the starting moment, which is much higher. All these measurements may seem complicated, but they are necessary for reliable operation of the gearbox.
Diagnostics of the condition of the gearbox (bearings, gearing) of VAZ and Lada Niva cars.
Now let's look at cases where tightening the nut alone is not enough. We will also talk about diagnosing the condition of the gearbox (bearings, gearing).
- Rotating the drive gear by the flange, we feel a uniform periodic increase and decrease in the moment of resistance - “roller busting”. This phenomenon is the stronger, the greater the preload, if both wheels are raised and, of course, in the case when the gearbox is removed and the differential box with the driven gear is removed from its housing.
“Roller busting” is a violation of the geometry of the raceways and bearing rollers, a sign that if the gearbox has not yet “hummed,” then this is about to happen. In the latter case, the matter may be aggravated by the appearance of waves on the gear teeth. Then the hum will turn into a howl - and the defect (waves on the teeth) cannot be eliminated.
If, while rotating the drive gear, you notice an increase and decrease in the moment of resistance in only one place along the angle of rotation, this means that pitting has begun on the outer tracks of the bearing (or bearings) - “pitting” has appeared. This also requires disassembling the gearbox.
- The shank nut is already tightened to the maximum torque (26 kgcm), but there is still no preload in the bearings. Moreover, there may be axial play. The fact is that the preload of the bearings is “metered” by their spacer sleeve.
As the bearings wear out, the bushing may turn out to be too long, and it is impossible to “settle” it by tightening the nut with a torque of more than 26 kgcm - it will take the form shown in the figure below, i.e. will fail completely. There is only one way out - after disassembling the gearbox and assessing the condition of the drive gear bearings, make the bushing shorter.
Shank bearing spacer.
- When the nut tightening torque is less than 12 kgcm, the resistance moment increases sharply. This most often indicates that the bushing has served its purpose - it has “shattered” and needs to be replaced. It is also possible that the crushing and wear of the ends of the parts have made the entire chain and the bushing itself shorter. You can “lengthen” the bushing by using spacer washers installed at the ends of the bushing.
Preventing the nut of the drive gear (shank) of the VAZ and Lada Niva gearbox from loosening.
Is it possible to prevent the shank nut from coming loose? The locking option is shown in the figure above. The nut rests through the bushing on the flange of the universal joint. The 12 mm sleeve size may require specification (adjustment) in place. The required size can be determined using plasticine by connecting the flanges with two bolts.
The standard spacer sleeve plays the role of a spring washer (one of the means of locking the shank nut), but spring washers, as a rule, are split and perform their role much better. Instead of a spring spacer, a rigid spacer can be used. In the absence of a spring spacer bushing, it is much easier to make a rigid one. A gearbox with a rigid spacer sleeve is used on rear-wheel drive Moskvich and IZH vehicles.
