How to replace the rear axle gearbox seal of a VAZ 2107

An oil leak from the axle gearbox through the drive gear oil seal is like a person with a runny nose. It seems that you are working as always, but this constant dampness under your nose is annoying. The only difference is that a person does not need the fluid flowing from the nose, but at the same time it is constantly produced by the body with a cold. And the bridge desperately needs the oil flowing out of the bridge, but it will not be able to replenish the supply without your help. It’s good that replacing the rear axle gearbox seal on a VAZ 2107 and other models of this series is possible with your own hands.

About the consequences of untimely “treatment”

And just as a runny nose can lead to serious problems in the body, even some kind of meningitis, oil leaking from the bridge can lead to serious “diseases” of the drive axle: overheating and jamming of bearings, scuffing on the surface of the gear teeth of the main pair, their rapid wear, increased noise and other troubles, including jamming of the main gear itself. Therefore, if you discover severe oiling in the area of the drive flange, or, even worse, an oil stain on the ground under the gearbox, you should not delay the “operation”. However, if “well, I can’t go on sick leave right now,” then by regularly monitoring and replenishing the oil level in the gearbox, the car can be operated for some time without any special consequences for the health of the bridge.

Assembly procedure

VAZ 2107: changing the oil in the gearbox

After the repair has been completed and all the damaged elements have been replaced, it is necessary to reassemble the rear axle and make sure that the gearbox no longer makes noise when driving.

The process looks like this:

the new node is fixed in the place intended for it;
return the axle shafts to the bridge;
the gear flange is attached to the cardan;
install wheels and brake drives.

It is necessary to test the car both at low speeds and at high speeds. First of all, leaving the car in neutral gear, press the gas. Then accelerate smoothly, and then turn off the engine. In a situation where the noise is still heard, an unambiguous conclusion should be drawn: you made some mistake or the reason was not in the gearbox.

When the car moves without any extraneous sounds, you can safely operate it as usual.

A little anatomy

In the last years of its life on the AvtoVAZ assembly line, the classic Zhiguli remained perhaps the only passenger car in the world with a rigid drive axle. This design is simple and technologically advanced in production, but has serious disadvantages in operation:

large unsprung mass of the bridge, which negatively affects the smoothness of the vehicle;
tendency to steer when one of the wheels hits an obstacle - at this time, due to the misalignment of the bridge, both wheels tilt from the vertical and tend to roll in the direction of the tilt;
reduction in the useful volume of the trunk, because there must be free space between the axle and the car body for the axle to move during the compression of the suspension.

The advantage of a rigid axle, in addition to manufacturability, is its better adaptability to bad roads: the ground clearance under the axle practically does not change depending on the load, and the wheel drive is reliably protected from external influences by the axle housing.

The Zhiguli bridge consists of a stamped-welded bridge beam (such beams are called “Banjo” for their characteristic shape), a main gearbox with a differential, and axle shafts. The gearbox is made in a separate open housing, the flange of which is bolted to the crankcase. A drive gear with a driveshaft mounting flange and a differential with a driven wheel are mounted in the housing on bevel bearings. The main gears are hypoid, that is, their axes are located at an angle of 90 degrees to each other, but do not intersect (they are crossed). The amount by which the axis of the drive gear is offset relative to the axis of the driven gear is called hypoid offset. Such a transmission, if it is precisely manufactured and well adjusted, operates smoothly and with the least noise, but due to the intense sliding of the curved teeth, it is very sensitive to the quality and quantity of oil in the bridge.

The design of the bridge is relatively simple and technologically advanced, although it is not without its drawbacks

Device

In order for the car to move, it is necessary to transfer the rotation of the engine to the wheels. But the engine speed is too high, and in order to correctly distribute the torque, a mechanism is needed that changes the gear ratio. Due to the gearbox and different engine speeds, the speed of movement changes, and the main pair of the rear axle takes over the rotation and transmits it to the wheels through gears.

flange, it is fixed on the drive gear (shank) of the RZM, and is an intermediate link between the driveshaft and this gear;
the shank of the main pair, at one end of which there are splines for pressing the flange, at the other end there is a bevel gear with a small number of teeth;
driven gear (planet gear), it is in mesh with the drive gear, and it is with it that it forms the main gear;
center differential, allowing the rear wheels to spin at different angular speeds.

The differential design is very simple - the mechanism consists of two axle gears, two satellites and a satellite pin. From the gearbox, the movement is transmitted to the axle shafts, on which the wheels are mounted.

Can't you spoil the porridge with oil?

Oil is poured into the axle housing up to the lower edge of the filler hole, in the position when the axle is installed and secured to the vehicle. You should not fill oil above this level, since a larger volume significantly increases power loss when the gears rotate and provokes leaks.

Lubrication of gearbox parts occurs as follows. The lower part of the driven wheel and differential are constantly immersed in an oil bath. When the car moves, they rotate, alternately wetting with oil all the teeth of the main gear and differential gears. The differential bearings and the rear pinion bearing are lubricated in the same way. In addition, the teeth of the driven wheel spray oil abundantly, creating “oil mist” in the crankcase. The least amount of oil when splashed goes to the front, most distant, bearing of the drive gear. To lubricate it, a channel is made in the upper part of the crankcase, where, under the influence of centrifugal force, oil is thrown from the outer circumference of the driven wheel. The higher the rotation speed, the more oil enters the channel. This channel leads into the cavity between the bearings of the drive gear, passes through the bearings and returns to the bridge beam. To drain oil from the flange side of the drive gear, there is an oil drain channel in the crankcase. The bearings, due to the conical shape of the rollers, have a pronounced pumping effect, so the flow of oil that flows from the front bearing directly to the oil seal can be quite significant - more than one liter per minute. It is not easy to withstand such pressure, so an oil-removing washer is installed immediately behind the bearing, in front of the oil seal. It slows down the flow rate, but there is still a gap between it and the crankcase through which the oil flows to the oil seal. Therefore, the tightness of the drive gear oil seal is a constant concern for axle designers and manufacturers.

The amount of oil supplied to the oil seal depends on the speed of rotation of the driven wheel of the final drive

But the lack of oil supplied to the oil seal is no less, and perhaps even more harmful to its “health”, because with dry friction against the surface of the flange, no matter how smooth it may be in appearance, the working edge of the oil seal will wear out very quickly, and a gap will form between it and the shaft, through which not only oil can flow out, but also water can flow in if you need to cross a ford or just a deep puddle in a heavy downpour. And water in oil is a very quick “death” for gears and bearings.

Removing the gearbox

Before starting work, that is, before starting to remove the rear axle gearbox of the VAZ 2107, it is necessary to drain the used oil from it. To do this, you need to unscrew the drain plug at the bottom of the rear axle, first placing a container to collect the oil. Typically, repairs involve replacing used oil with new oil.

Next, unscrew the screws securing the propeller shaft flange and disconnect it from the shank. Jack up the rear of the car and remove the rear wheels. After unscrewing the guide screws, remove the brake drums to gain access to the axle shafts. Having unscrewed the bolts securing the axle shafts (4 pcs.), we remove the axle shafts from the rear axle, thereby completely freeing the gearbox. All that remains is to unscrew the bolts securing the gearbox to the rear axle beam and remove it. After removing the axle shafts, it is recommended to check whether the bearings require replacement.

Surgery or therapy?

So, our “wounded” axle is leaking oil around the drive gear flange, and we are ready to save it. But first, as is usual with serious doctors, you need to figure out the cause of the “disease.” How does an appointment with a local therapist usually begin? Of course, from measuring temperature and pressure. You may be surprised, but when starting to repair a bridge, we should also remember these physical characteristics. And that's why. During operation, the drive axle gets quite hot - the temperature in the crankcase can reach 80 degrees Celsius. And since, ideally, the axle housing is a sealed container, along with heating in a confined space, the pressure also increases. This is the law of physics. The increased pressure additionally loads all the seals and gaskets of the bridge, breaking out where, for some reason, there is less resistance. This is often the drive gear seal, which is subject to the most intense friction. To reduce pressure, a valve (breather) is installed on the axle housing, which releases excess pressure. Therefore, the first thing you need to start diagnosing a leak is by checking the functionality and cleaning the breather from dirt. The valve cap should rotate freely. When you lightly press the cap from above, it should move freely and return to its original state when the load is removed.

If cleaning the breather does not help, and the leak continues, it’s time to prepare “surgical instruments”. In our case, a regular plumbing kit will be enough, although it would be nice to grab another skein of thread and a hand balance scale (dynamometer) with a good scale.

Design and technical characteristics of the gearbox

The rear gearbox of the VAZ 2107 car consists of a massive steel casing with a shank, a driveshaft flange, two main gears mounted at right angles to each other and a self-locking differential.

The main elements of the gearbox are the housing, the main pair of gears and the differential with satellites

Rear gear ratio

The main characteristic of any gear transmission is its gear ratio. It is the ratio of the number of teeth on the driven gear to the number of teeth on the drive gear. The driven gear of the VAZ 2107 rear gearbox has 43 teeth. And the drive gear has 11 teeth. Dividing 43 by 11 we get 3.9. This is the gear ratio on the VAZ 2107 gearbox.

Another important point should be noted here. VAZ 2107 was produced for many years. And over the years, gearboxes with different gear ratios were installed on it. For example, the earliest models of the “seven” were equipped with gearboxes from the VAZ 2103, the gear ratio of which was 4.1, that is, the tooth ratio was 41/10. On later “sevens” the gear ratio changed again and was already 4.3 (43/10) and only in the newest “sevens” this number is 3.9. Due to the above reasons, the driver often has to independently determine the gear ratio of his car. Here's how it's done:

the car is set to neutral gear;
The rear of the car is raised using two jacks. One of the rear wheels is securely fixed;
After this, the driver manually begins to turn the driveshaft of the car. It is necessary to make 10 revolutions;
By rotating the driveshaft, you need to calculate how many revolutions the unfixed rear wheel will make. The number of wheel revolutions should be divided by 10. The resulting number is the gear ratio of the rear gearbox.

Bearings

The rotation of all gears of the gearbox is ensured by bearings. In the rear gearboxes of the VAZ 2107, single-row roller bearings are used on the differential, and the rollers there have a conical shape. Bearing marking is 7707, catalog number is 45–22408936. The price of a bearing on the market today starts from 700 rubles.

All rear gear bearings of the “seven” are roller, single-row, tapered

Another bearing is installed in the gearbox shank (i.e., in the part that connects to the cardan). This is also a tapered roller bearing marked 7805 and catalog number 6–78117U. Standard VAZ shank bearings today cost from 600 rubles and more.

Planetary pair

The main purpose of the planetary pair in the rear gearbox of the VAZ 2107 is to reduce engine speed. The pair reduces the crankshaft speed by about 4 times, that is, if the engine crankshaft rotates at a speed of 8 thousand rpm, then the rear wheels will rotate at a speed of 2 thousand rpm. The gears in the planetary pair of the VAZ 2107 are helical. This solution was not chosen by chance: a helical gear is almost twice as quiet as a spur gear.

The planetary pair has a helical gear to reduce noise levels

But helical planetary pairs also have a disadvantage: the gears can move along their axes as they wear out. However, this problem is relevant for racing cars, the rear axles of which have exclusively spur gears. And for all the years of production of this car, the VAZ 2107 had exclusively helical planetary pairs.

Tell me, doctor, is there any way to do without surgery?

First of all, you need to drain the oil from the bridge. To do this, we turn out both plugs - both the drain and the filler. Next, disconnect the driveshaft from the bridge. When separating the axle and cardan flanges, be careful - sometimes oil accumulates in the cavity between the flanges. If this happens, then check the axial play of the flange by rocking it along the axis with your hand. There shouldn't be any play. If there is noticeable movement (in fact, play of more than 0.05 mm is already very harmful for the bridge), it is worth once again carefully inspecting the traces of oil on the crankcase. Perhaps the oil leaked not through the cuff, but through the gaps in the splines of the loose flange? In this case, it is worth trying to eliminate the play and observe the bridge in operation. If the leak stops, then that was the reason.

Axial play of the flange is eliminated by tightening the nut. When handling a flange nut, you should always remember that it does more than just hold the flange. This is the most important element in adjusting the drive gear bearings, and improper tightening can have serious consequences, ranging from noise to axle jamming. Having inserted two bolts into the holes of the flange, we insert the mounting between them so that, holding it, we prevent the rotation of the flange when the nut rotates. Pull the nut just enough to select the gap. The thread pitch is 1.25 mm, which means that when you turn the nut one turn, it will move along the axis by the same 1.25 mm. If the flange play is minimal - 0.05 mm, then it is enough to turn the nut 1/25 of a turn, that is, only 15 degrees.

Overtightening the nut loads the drive gear bearings with a large axial force, as a result they overheat and may fail. To be sure that we did everything correctly, we need to measure the moment of resistance to rotation of the drive gear. To do this, you need to remove the rear wheels and brake drums, unscrew the axle shaft mounting bolts and pull off the axle shafts, disengaging them from the differential gears. Then we tightly wind the thread onto the flange shaft and pull its free end with a steelyard, measuring the force at which the flange rotates evenly without jerking or acceleration. A less accurate result is obtained by another method, when the steelyard is hooked to a hole in the flange and also pulled evenly. In this case, care must be taken to ensure that the force is directed perpendicular to the radius of the flange circumference. You can also use a torque wrench, evenly rotating the drive gear shaft by the nut, but with such a movement it is difficult to follow its readings. We multiply the measured force value by the radius value, thereby obtaining the moment of resistance to rotation. The torque value should be in the range of 6–9 kgf.cm.

Torque wrenches usually have a scale marked in Newton meters (N.m). One kilogram-force per centimeter (1 kgf.cm) is equal to 0.098 newton meters, or approximately 0.1 N.m.

You can try to do without removing the axle shafts and measuring the torque on the flange. Experienced mechanics can do this. To do this, tighten the nut exactly until the play is eliminated and a little more. After this, we put the driveshaft in place and make a test drive in a mode sufficient for the bridge to warm up to operating temperatures (several tens of kilometers along a country road). After this, we check by hand the heating of the axle housing in the area of the drive gear bearings. If the hand tolerates heat, then we assume that everything is in order. If the bearings have become so hot that a drop of water on the crankcase hisses, then we have overdone it and now we definitely cannot do without a good adjustment. You cannot reduce the moment of resistance to rotation of the drive gear simply by loosening the nut. The fact is that a deformable spacer sleeve is installed between the bearings, which, when the nut is tightened, gives the structure the necessary rigidity. By tightening the nut, we compressed the bushing more than necessary, and it will no longer be able to lengthen back. When we loosen the nut, the bushing is no longer “spacer”, so it needs to be replaced. You should also pay attention to the bearings. If a blue color appears on the rolling surfaces, it means they have overheated and also require replacement.

How to remove the gearbox

VAZ 2107 axle shafts: removal and installation, oil seal replacement
Before starting the removal procedure, you need to completely drain all the oil that is in the rear axle. To do this, place a suitable container over it and unscrew the plug. Be sure to fill in new oil after all repair work and installation of the gearbox in place.

The repair procedure is as follows:

Unscrew the bolts that secure the propeller shaft to the rear gearbox flange.
The rear half of the driveshaft must be disconnected and lowered down so that it does not interfere with work. During assembly, tightening is carried out with a torque of 18 kgf/m.
Remove the rear wheels.
Unscrew the guides that are located on the brake drums.
Completely dismantle the brake drums and unscrew the four bolts that secure the axle shaft.
Only after this can the axle shaft be pulled out.
To dismantle the gearbox, you need to unscrew the 8 bolts that secure it to the rear axle.
After all the measures taken, you can completely remove the gearbox from the car.

Be sure to check the condition of the rear axle bearings. If they become unusable, then they need to be replaced.

Let's go to the store

So we did everything we could, but the leak didn't stop. This means it's time to change the seal. Actually, according to GOST, these products are called “Reinforced rubber cuffs for shafts.” Or simply - cuffs. If a store offers you a part with that name, don’t be surprised. Factory part designation: 2101–2402052. Further, its variations can be written through a dash: -01, -02 and so on. All of these products are interchangeable and differ in the nuances of their design and manufacturer. Perhaps the most important thing when choosing an oil seal is the manufacturer. Choose products from well-known factories. No name details, in principle, should not attract your attention, because not only according to ours, but also according to Western standards, the cuff must be marked with the manufacturer’s trademark, cuff size, and type of material. Domestic GOST also provides for marking the year of manufacture. As a rule, these are two digits of the year when the mold was made, and next to them are dots, each of which indicates one year of operation of this equipment. You count the points, add their number with the numbers and find out in what year your part was manufactured. The year of manufacture is important because over time, any rubber compound “ages”, losing its shape and elasticity .

The type of mixture from which the oil seal is made is also important. The most expensive and most durable is fluorine rubber. It works well in aggressive environments and at high temperatures. It is usually marked with the Latin letters FBR. Nitrile butadiene rubber (NBR) is considered optimal in terms of price and quality for automobile transmissions. ACM acrylate polymer seals are also available, but they are usually used in components that should not be directly exposed to water. Chemists are constantly improving their products, so the fundamental differences between mixtures are becoming less and less, due to additives introduced into them that improve the weaknesses of certain recipes. Read reviews on the Internet, listen to the seller’s recommendations and make a decision based on your financial capabilities.

When examining externally, first of all pay attention to the quality of the working edge: it should be even and smooth around the entire circumference. You can use a magnifying glass. It will be a big plus for the gearbox seal to have an external boot - like a second edge, but without a spring and with a hole of a slightly larger diameter. The boot, as the name suggests, protects the work area from dust and dirt. The presence of an inclined notch on the boot or near the working edge indicates that the oil seal is designed for shafts rotating in the same direction.

When and why to change the front oil seal

The manufacturer recommends replacing the front crankshaft oil seal of VAZ 2101-2107 engines every 150,000 km. However, in practice such replacement has to be performed more often. Accelerated wear of the sealing element and the appearance of engine oil leaks are caused by:

skewed oil seal during installation;
loss of elasticity due to engine overheating;
increased radial runout of the drive pulley of mounted units;
use of low-quality motor oil;
wear on the crankshaft pulley hub.

In addition, we cannot rule out hardening of the cuff due to natural aging and the possibility of a manufacturing defect - unfortunately, the quality of parts for rear-wheel drive VAZ models leaves much to be desired.

It is impossible not to notice damage to the sealing element - the rotating pulley scatters oil in the front of the engine and throughout the engine compartment. However, do not think that such a malfunction only leads to oiling of the units and a decrease in the lubricant level. If engine oil gets on the generator belt and other rubber parts, it can quickly render them unusable.

Keep in mind that the appearance of a leak through the engine seals is provoked by another factor - increased crankcase gas pressure. For this reason, be sure to check the cleanliness of the engine ventilation system.

Something else useful for you:

Replacing the rear crankshaft oil seal of a VAZ 2101-2107 with your own hands
Replacing valve stem seals: main signs of wear, replacement procedure
DIY crankshaft bearing replacement for VAZ 2105-2107

“Quiet, the operation is underway!” or Replacing the rear axle gearbox seal on a VAZ 2107

The sequence of work when replacing the gearbox seal is as follows:

We measure and record the moment of resistance to rotation of the flange (the axle shafts must be removed!) .
Unscrew the flange nut.
Remove the flange from the shaft splines.
Using expansion pliers, remove the oil seal. If you don't have pliers, you can pry it off with a screwdriver. Be careful not to damage the surface of the socket.
We inspect the flange. If its surface has a pronounced groove in the place where the working edge of the oil seal rubbed, then before installing the new oil seal, insert a washer 1 mm thick into the socket. If the flange is damaged on the working surface, replace it with a new one.
Lubricate the outer surface of the oil seal with lithol and carefully drive it into the crankcase socket using a mandrel of suitable diameter. If there is no mandrel, press in the oil seal by evenly tapping the end along the circumference of the outer diameter. Make sure that there are no distortions - the working edge should be strictly perpendicular to the shaft axis.
We inspect the lead-in chamfer on the flange. It should not have defects that could damage the working edge. We install the flange, avoiding sudden movements and impacts, so as not to knock the spring off the oil seal. Before installation, you can lubricate the flange chamfer with transmission oil to make the process easier.
We tighten the nut, periodically checking the moment of resistance to rotation of the flange. Remember that at the end of the tightening, the resistance in the bearings increases much more intensely than at the beginning . The moment of resistance to rotation should be 1–2 kgf.cm greater than what we recorded before unscrewing the nut. In any case, if the moment exceeded 9 kgf.cm, and the bearings in the bridge were still old, remove the flange again, take out the inner ring of the bearing and change the spacer sleeve. If the bearings are new (new means they have not traveled a single kilometer, because after a hundred kilometers they can be considered old for adjustment purposes), then the normal moment of resistance to rotation after tightening the nut for them should be in the range of 16–20 kgf. cm. Replacing the rear bearing will affect gear alignment, so please refer to the appropriate manual for this procedure .

To prevent self-loosening, the flange nut has a special plastic insert, which, when crushed against the thread, creates additional resistance both when screwing and unscrewing. As a rule, such nuts can withstand up to ten unscrewings without losing their locking properties. If in doubt, get a new nut.

We reinstall the axle shafts and brake drums, screw on the driveshaft, and fill in the oil. We make a test drive and if everything is in order, we enjoy life, until we suddenly find a treacherous spot under the bridge again...

Important nuances

The dynamometer readings were mentioned above, and this is no coincidence. Tightening the flange is a very responsible process, and it can only be done using a torque wrench. This allows you to avoid excessive squeezing of the oil seal, which leads to a violation of the tightness of the entire gearbox. This is done like this: if at the first measurement the force on the dynamometer was 2.8 - 3 kg, then the force on the torque wrench when tightening should not exceed 6.3 kg. If the dynamometer showed 4.3 kg, then when tightening the key there should be no more than 9 kg, etc. If the dynamometer showed 2.7 kg, and the key when tightened shows 9 kg or more, it means that the gearbox adjusting sleeve is completely worn out and needs for urgent replacement.
After removal, the flange should be carefully inspected for severe abrasions and cracks. If there are any, the flange must be replaced. If this is not done, the new oil seal will very quickly become unusable.
Before driving the oil seal with a tube, it is recommended to lubricate it with lithol. This makes it much easier to fit the new oil seal into its original place.
When striking a pipe with a hammer, there is no need to be too zealous: with a strong blow, the pipe easily cuts the seal.

As you can see, replacing the oil seal itself does not take too much effort, and getting to it is not so difficult: just put the car in an inspection hole with good lighting. But tightening the flange so that it does not crush the new oil seal is a more difficult task. That is why the car owner needs a dynamometer and a special key, without which it is strictly not recommended to open the rear axle gearbox.