Bad luck


On VAZ 2107 with a screech, first gear is engaged

(car mileage - not less than 100 thousand km). What is the reason? Is it necessary to disassemble the box?

Edward CONOP

"Zhigulevskaya" gearbox is one of the best among Russian ones both in terms of strength, reliability and durability, as well as in simplicity of design and maintainability. "Lada" is still popular not least because of the gearbox, rarely let the owner. But nothing lasts forever: sooner or later, the car will throw a “headache” to the owner.

Most gearbox defects can only be truly repaired after disassembly. But sometimes it is possible, taking precautionary measures, to postpone a serious repair - for example, until returning from vacation, a business trip, etc.

So, if synchronizers do not work well, although the rest is in order, it is useful to recall the tricks of using the box without synchronizers. Our grandfathers traveled - and quite successfully!

The circuit in fig. 1 shows a simple transmission device. From the flywheel 1 of the engine, the rotation is transmitted to the clutch 2 and the gearbox input (primary) shaft 3 connected thereto. Then, through a pair of gears Z1 and Z2, constantly coupled, the intermediate shaft 5 is rotated (“gear block”, since this is a single part), and gear 9 (Z4) is driven through gear Z3. But in the position shown in the diagram, it rotates freely relative to the driven (secondary) shaft 6 - and power is not transmitted to the main gear 10 and the drive wheels. This is neutral.

An important detail of the gearbox control mechanism is the coupling 8, which is capable of sliding under the action of the fork 7 along the slots of the driven shaft 6, while at the same time rotating together with it as a whole. If you move the clutch until it engages with gear 9, the latter will also connect to the driven shaft - the gear is engaged! Now, the engine torque increased by the gearbox will be transmitted to the driven shaft, and then to main gear 10 and to the drive wheels.

A fragment of a real construction is shown in fig. 2. The sliding clutch 1 can be moved, including the first (right) or second (left) gear. Partially "moving out" from the splines of the hub 3, rigidly connected with the driven shaft 10, the coupling is connected to the splines of the hub of the gear 7, provided that the speed of rotation of the gear is equal to the speed of rotation of the clutch. The latter is connected with the driven shaft, and therefore with the wheels. But how to balance these speeds if the synchronizer is faulty?

As an example, we show how to switch from second gear to first. For example, on a VAZ 2106 the tachometer shows 2000 rpm. Squeeze the clutch … Turn off the second gear … The speed of rotation of the gear 7 decreases, and the clutch 1 is almost unchanged, as the machine rolls by inertia. If you "stick" the first gear by force now, the rattle is inevitable, since the leading branch of the system - from the clutch disc to gear 7 - has inertia, which the splines must overcome!

So, you need to release the clutch pedal and “tighten up” the gear with the engine, raising its speed to three thousand. And after the “re-gasing” - squeeze the clutch again … and when the gear rotation speed decreases, it draws closer to the clutch speed, the transmission will engage without problems.

By the way, as the experience of many owners has shown, a “Zhiguli” gearbox, if synchronizers failed, and the rest is in order, can safely serve another tens of thousands of kilometers. You just need to know how to use it. The skill in switching is acquired quickly, in a few workouts. By the way, it is recommended to switch gears from lowest to highest even on perfectly functioning "Lada" without rushing, with a small pause between turning off one and turning on the other, and without a pause - from higher to lower, to facilitate the work of synchronizers and extend their service life.

When starting off, a double squeeze is not needed: the clutch 1 is stationary (the wheels are standing), so it is enough to squeeze the clutch so that gear 7 also stops and the gear is easily engaged. Do you hear a rattle? So the clutch is not completely off. Perhaps it "leads." If the transmission “rests in silence”, does not enter, it means that the sharp input edges of the synchronizer teeth are worn out: in this case they often abut like forehead to forehead … (The new ones resemble sharp teeth in shape!) Then you need to slightly release the clutch to turn gear - and the transmission will “enter”.

That’s all science! But current motorists spoiled by synchronizers, as a rule, do not own it. That is why it is precisely the synchronizers that are the first to surrender, when other parts of the box still work and work.

Where to start in your case? Take advantage of the fact that there is a hatch at the bottom of the box. If you remove the cover (of course, drain the oil before this), you can see many details - and, after evaluating them, make this or that decision.

Inspect how much this succeeds, the synchronizer parts shown in fig. 2, as well as the contents of deposits on the inside of the hatch cover. If there are metal particles, shavings, and even more so large debris, then the box is really “sick”.

If no pieces of metal were found, then the synchronizer is most likely simply worn out and can no longer cope with a serious load. Here, in addition to the blunted edges already mentioned, the main role is played by the condition of the conical friction surfaces in the coupling 1 and on the locking ring 5. If the “thread” is worn out (oil is displaced poorly), and the gap A has disappeared, then the synchronizer is inoperative.

You can fix this only by replacing the parts. How urgent - you decide! There is an opportunity to quickly, reliably, not very expensive to repair the unit - proceed. No - re-learn the double squeeze and ride "until better times."

Of course, getting into the taste of our reasoning, you continue: they say, the process of engaging the gear also depends on the wear of the fork 2 and the groove in the coupling 1. If the wear is so great that the clutch “runs” only at the very ends of the splines of the gear hub 7, then these places, in turn, quickly wear out - and once the transmission spontaneously, under load, turns off. In the future, this will happen all the time … But you haven’t gotten it yet.

And finally, the last, rather unpleasant option: from the inside of the cover you found pieces of steel wire - fragments of a spring 6 synchronizer. True, if you are careful, you should have heard a suspicious noise shortly before: imagine spinning gears, and nearby - hefty pieces of wire! In other words, if you still don’t find broken teeth, then you are a real lucky one. It is necessary to clean the box of metal debris, rinse and especially carefully examine the gears. If at least one tooth is broken off, the unit must be repaired immediately, otherwise you will get to the purchase of a new box - and it is more expensive than repair.

But if the damage to the teeth is small (minor chips, dents, etc.), you can ride on what you have for some time. In critical situations, away from home - no one will blame you! Especially if you soberly assess what has happened and are “adequate, ” act cautiously.

… But now you removed the fragments of the spring from the box, examined the parts, found them in perfect order … Can I install the hatch, add oil and go? Can. But it’s better not to rush - and do a useful operation to rid the box of a kind of “appendix” that can one day ruin your mood. This is a washer 9, in which the spring 6 used to abut. Than not a "superfluous detail"!

Having got rid of the spring pressure, the washer quickly wears out under the influence of vibrations - and begins to “walk” along the splines of the hub 7 of the driven gear of the first gear, getting close to the ring 5, which, we note, is now also superfluous. The trouble is that sometimes the washer 9, skewed, does not allow the clutch and ring to move to the driven gear - and does not allow the shift lever to move.

If in this situation the "wedge" by itself, from the action of vibrations, does not disappear, you will have to remove the hatch to get to the obstinate washer. So is it not better to get rid of her in advance, without waiting for adventure? It is steel, but thin - you can simply break it out with a suitable tool.

Fig. 1. Scheme of the simplest transmission: 1 - engine flywheel; 2 - clutch disc; 3 - the drive shaft of the gearbox; 4 - gearbox housing; 5 - an intermediate shaft; 6 - driven shaft; 7 - a switching plug; 8 - sliding clutch; 9 - driven gear of the first gear; 10 - main gear.