SHRUS crunches. How to check and troubleshoot

In the front suspension of a front-wheel drive car there is a part with a strange at first glance name CV joint. And not just one, but four. The tricky name means "a hinge of equal angular velocities". In the technical literature, the term homokinetic hinge is usually used. Outwardly, the CV joint resembles a grenade, which is why the people called it that way. But for most motorists, neither the form nor the decoding of the abbreviation explain what this part is intended for. Let's try to figure it out, and at the same time find out how the CV joint malfunction manifests itself and how to determine which of the hinges is the source of the problem.

What is a constant velocity joint for?

The main feature of the front-wheel drive is that the rotation has to be transferred to the wheels, which not only move up and down during movement, but also turn at a significant angle.

In the driveline, which was originally used for this purpose, the deviation from the coaxial arrangement of the shafts leads to a decrease in the angular velocity of rotation of the driven shaft relative to the drive shaft. And the steeper the turn that the car makes, the slower the rotation of the driven axle shafts. As a result, all this resulted in a loss of power, jerks in corners and a stressful operation of the transmission as a whole, which means rapid wear and a reduction in the service life of its parts. Cardan joints themselves also did not differ in longevity.

The invention of the hinge of equal angular velocities radically changed the situation. Its use allows the axle shafts to rotate at a constant angular speed, even if the wheels are turned at a significant angle. As a result, the absence of vibrations and jerks is ensured, and most importantly, the transfer of rotation from the motor to the wheels is carried out without significant power losses.

Varieties of CV joints and their design features

On each of the semi-axes there are two CV joints. That is, in a front-wheel drive car, there are only four grenades - two internal and two external.

Internal and external hinges differ functionally and structurally. The internal one is located near the gearbox and is designed to transmit torque from the axle shaft. Its working angle, as a rule, does not exceed 20°, but at the same time it allows some displacement along the axis, thus providing the possibility of changing its length. Shortening or lengthening the drive shaft is necessary to compensate for suspension travel.

The outer CV joint is mounted on the opposite end of the axle shaft, next to the wheel. It is able to work at an angle of about 40 °, providing rotation and rotation of the wheel. It is clear that the external grenade works in more stressful conditions, and therefore fails somewhat more often than the internal one. The dirt flying from under the wheels also contributes to this, the external CV joint clearly gets more of it than the internal one.

There are a number of design varieties of constant velocity joints. However, in our time in cars you can mainly find two types of CV joints - “Tripod” and Rzeppa ball joint. The first one does not have a large working angle, but it is reliable and relatively cheap, and therefore it is usually used as an internal hinge. It uses rollers that are placed on a three-beam fork and rotate on needle bearings.

The second one has a much larger working angle, so it is logical that it is used as an external CV joint. It is named after the mechanical engineer Alfred Rzeppa (the incorrect pronunciation of Rzeppa is also common), a native of Poland who worked for the Ford company. It was he who, in 1926, created the design of a constant velocity joint with six balls, which are held in the holes of a separator placed between the body and the inner race. The movement of the balls along the grooves on the inner race and from the inside of the housing makes it possible to change the angle between the axes of the driving and driven shafts over a wide range.

Zheppa's CV joint and its modernized varieties ("Birfield", "Lebro", GKN and others) are still successfully used in the automotive industry.

Causes of a crunch in the SHRUS

By themselves, the constant velocity joints are very reliable and may well last for a couple of hundred thousand kilometers, or even longer. Unless, of course, you do not allow dirt and water to get into them, change anthers and lubricants in time, drive carefully and avoid bad roads.

And yet grenades also fail sooner or later. For one reason or another, workings appear in the cage or hinge body. The balls rolling inside hit them, emitting a characteristic dull metallic thud. Then they talk about the “crunch” of the CV joint.

Backlash and wear occur due to natural wear or as a result of improper operation. There can be several reasons, but the most common is a damaged anther. Through breaks in the protective rubber boot, oil flies out, leaving the rubbing elements of the hinge without lubrication. In addition, through cracks in the anther, moisture, debris, sand enter the CV joint, which act as an abrasive, accelerating the wear of the grenade. The condition of the anthers should be checked regularly - every 5 ... 6 thousand kilometers, and at the slightest sign of damage, change without hesitation. A rubber boot is much cheaper than a CV joint.

The second most common factor leading to premature wear of grenades is an aggressive driving style. Extreme driving over rough terrain and a sharp start to movement at the moment when the wheels are turned out are especially detrimental to CV joints.

Another possible reason is engine tuning with power buildup. It can significantly increase the load on the transmission. As a result, its elements, including CV joints, will be subject to faster wear.

If the grenade began to knock a short time after the replacement, you may have come across a defective copy or a fake. But it is impossible to exclude errors during installation that can disable a new high-quality hinge. Therefore, if you are not very confident in your abilities, it is better to entrust the replacement of CV joints to specialists.

Why does the hinge crunch at low temperatures

Lubrication is of particular importance in ensuring the long-term proper operation of the CV joint. Its condition must be monitored and periodically changed. But you can’t stuff the first lubricant that comes to hand into a grenade. The use of graphite grease is strictly prohibited. For CV joints, a special oil is produced, as a rule, containing molybdenum disulfide as an additive. It has water-repellent properties and is able to soften shock loads. This is how it should be applied. To properly replace the lubricant, the grenade must be removed, disassembled and thoroughly washed.

The quality of the lubricant is not always up to the mark. Some varieties do not tolerate frost well and may thicken at low temperatures. Then the pomegranates start to crackle. The internal CV joints warm up quite quickly and stop knocking, while the external ones can continue to make noise much longer. In such cases, it is better to avoid sharp turns and accelerations until the crunching stops. Probably, you should choose a better lubricant that can ensure the normal operation of the hinges in frosty weather.

What happens if you ignore the problem

CV joints do not fall apart overnight without any preliminary symptoms. Internal defects and wear appear gradually, and the process of destruction of the part takes a long time. Therefore, for some time with crispy hinges you can ride, but if possible, sharp accelerations and turns at high speed should be avoided. It is also important not to miss the moment and not let the grenade collapse. It is possible that other parts of the transmission will also be damaged. With a collapsed CV joint, the car will not be able to move, and you will have to deliver it to the garage or to the service station using a tug or tow truck. In some cases, a stuck CV joint can lead to loss of vehicle control. It is hardly necessary to explain what consequences this may have.

Therefore, if it rattled or crunched in the suspension, do not put off finding out the reasons and determining the culprit of the problem. Moreover, sometimes a crunch means just a lack of lubrication, and such a malfunction is eliminated relatively simply and cheaply.

Identifying a Specific Faulty Hinge

Since there are four CV joints in a front-wheel drive car, it is important to isolate the malfunction and determine which of the grenades needs to be replaced or at least lubricated. Many do not know how to do this, although in many cases everything turns out to be not so difficult.

First of all, of course, you should do a visual inspection. If the anther is damaged, then the CV joint definitely requires at least dismantling, prevention, lubrication and replacement of the protective rubber boot, and as a maximum - replacement. Damage to the boot will be indirectly indicated by grease splashed on neighboring parts.

Try to rotate the hinge around the axis by hand. A serviceable CV joint should remain motionless. If there is play, then the hinge must definitely be replaced. However, it will be more reliable to determine the presence or absence of backlash by dismantling the axle shaft with grenades and holding it in a vise.

Determination of a faulty external CV joint

The greater the angle between the drive and driven shaft, the greater the load experienced by the hinge, especially if at the same time it receives a significant torque from the motor. Hence the easiest way to determine a faulty external CV joint. Turn the steering wheel as far as possible to the left or right and start moving sharply. If the crunch appears when the wheels are turned to the left, then the problem is in the left outer grenade. If it starts knocking when the steering wheel is turned to the right, you need to deal with the right outer hinge. The sound, as a rule, is heard quite distinctly and can be accompanied. Symptoms are usually quite pronounced and do not cause doubts. If the sound is weak, especially on the right side, then it is better to ask an assistant to listen.

Determination of a faulty internal CV joint

A faulty internal CV joint often does not manifest itself in such a clear way. If the road surface is even, the problematic inner grenade will usually begin to make sounds at high speed or during acceleration, when the load on the hinge increases. Vibration and jerking of the machine are also possible here. At low to medium speeds, an inboard joint crunch can be heard when driving in a straight line on rough roads, especially when the wheel hits a pothole.

You can choose a suitable pothole, fortunately, their choice on domestic roads is very wide, and try to drive through it first only with the left wheel, then only with the right. If a metallic crunch occurs in the first case, then the left inner CV joint is under suspicion, if in the second, check the right one. Just do not overdo it, otherwise in this way you can ruin a serviceable grenade.

And do not forget that similar knocks while driving on a bad road can also come from parts.

Another method suitable for both types of CV joints

If you have a jack handy, you can check all four hinges and more accurately determine which one is the source of the problem. The procedure is:

1. Set the steering wheel to the middle position.

2. Hang one of the front wheels.

3. Engage the handbrake, put the gear lever in neutral position and start the engine.

4. After depressing the clutch, engage 1st gear and gradually release the clutch pedal. The hung wheel will start spinning.

5. Load the CV joints by gently applying the brake. The problematic internal hinge will make itself felt with a characteristic crunch. If both internal grenades are working, then there will be no extraneous sounds, and the engine will start to stall.

6. Now turn the steering wheel as far to the left as possible. A failed inner hinge will still make noise. If the left outer grenade has internal workings, it will also thunder. Accordingly, the sound will become louder.

7. Similarly, check the right outer CV joint by turning the steering wheel all the way to the right.

After completing the test, place the gearshift knob in neutral, stop the engine and wait until the wheel stops spinning. Now you can lower the car to the ground.

The solution

Having identified the problematic hinge, you need to dismantle it, disassemble it, rinse thoroughly and inspect it. If there are workings, damage, backlash, the CV joint should be replaced with a new one. There is no point in repairing it. Attempting to sand work surfaces is likely to be a waste of time and effort and will not give a lasting effect.

If the part is in order, after washing it should be filled with special grease for CV joints and returned to its place. The same should be done with the new hinge. As a rule, for an internal grenade you need about 100 ... 120 g of lubricant, for an external one - a little less. Lubrication during assembly must also be laid under the anther, and then securely tighten it with clamps on both sides.

Since errors during the installation of CV joints can lead to their premature failure, it is better to carry out this procedure for the first time in the presence of a more experienced motorist who will explain all the details of the process along the way.

When replacing parts that have a symmetrical pair in the machine, you should be guided by the general rule - change both elements at the same time. This rule should also be applied to CV joints, but with one important clarification: never remove both axle shafts at once in order to prevent displacement of the differential gears. First, work with one axle shaft and install it in place, only then you can dismantle the second one if necessary.

Cheap hinges, produced under little-known brands, are often made of low-quality metal and are not very carefully assembled; there are also initially defective parts. Such products should be avoided. You should also be careful when choosing where to buy. In the online store you can purchase the necessary spare parts for transmissions, suspensions and other systems of cars made in China and Europe.

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