The constant velocity joint, or simply CV joint, is one of the key elements of the transmission of a front-wheel drive vehicle. It is this unit that transmits torque from the gearbox to the wheels, allowing them to rotate at the same speed even when turning the steering wheel or driving over uneven surfaces. Unlike the cardan shaft, grenade (as CV joints are often called popularly) is capable of operating at large angles, which is critical for a modern suspension.
Among all types of hinges, it is the internal one that often remains in the shadow of its external counterpart, although its wear can lead to much more serious consequences. Many drivers confuse the sounds made by the external and internal grenade, which leads to the purchase of unnecessary spare parts. Understand how the inner CV joint knocks, can be difficult without experience, since the nature of the noise is radically different from the usual crunch of an external grenade when turning.
In this article we will analyze in detail the acoustic signs of a malfunction, accurate diagnostic methods and nuances that will help you avoid costly mistakes during repairs. Ignoring the first symptoms can lead to complete destruction of the unit right on the road, which can lead to an accident and costly evacuation.
Design features and causes of wear
The internal joint is usually a tripoid type design where needle bearings ride in grooves in the housing. Unlike the external hinge, which works primarily by twisting and turning, internal CV joint experiences enormous axial loads. It constantly moves back and forth inside its cage, compensating for changes in drive length when the suspension operates.
The main cause of failure is a ruptured boot. The ingress of even a small amount of abrasive dust or moisture leads to leaching of the lubricant and the formation of scuffs on the working surfaces. Metal shavings formed during friction act as an abrasive, accelerating the destruction of the mechanism exponentially.
It is also worth noting that the resource of the node directly depends on the quality of the roads and driving style. Sharp starts from a standstill, especially on cars with powerful engines, create peak loads on the tripod, causing its premature wear. In some cases, the cause may be a manufacturing defect or poor quality materials.
- 🛑 Rupture of the elastic boot and loss of lubricant.
- 🛑 Abrasive particles getting inside the mechanism.
- 🛑 Mechanical damage from hitting curbs or stones.
- 🛑 Natural aging of metal and fatigue damage.
It is important to understand that the internal joint often fails before the external one precisely because of the more complex kinematics of movement. If the outer one simply spins, then the inner one also performs reciprocating movements, which requires the ideal condition of the rolling surfaces.
Characteristic sound: how to distinguish the knock of the internal CV joint
The surest way to understand how the inner CV joint knocks, is to analyze the behavior of the car during acceleration. Unlike the external grenade, which crunches when the wheels are turned, the internal one emits a dull, metallic knock or rhythmic clicking sound precisely at the moment of acceleration. This sound is often confused with engine or suspension knocking.
The sound is most pronounced when you press the gas pedal hard. At this moment, the tripoid extends as far as possible from the body, and if there is play there, an impact occurs. As soon as you let off the gas or settle into a steady drive, the noise may disappear completely, which can be confusing for inexperienced drivers.
⚠️ Attention: If during acceleration you hear a distinct knocking noise that disappears when coasting, do not delay diagnostics under any circumstances. Continued operation may result in the drive jamming.
Interestingly, at low speeds the knock may be barely noticeable, but as the engine speed and shaft rotation speed increase, the frequency of the knocks increases. Experienced craftsmen often say: “The grenade knocks when given a job.” This means that under load the defect is most pronounced.
To more accurately determine the source of the noise, try accelerating in different gears. If a knocking noise is heard in all gears when accelerating, then with a high degree of probability the problem is precisely internal CV joint. The sound may also increase when driving on rough roads, but in this case it is more difficult to separate it from the knocking of the suspension.
Symptoms of malfunction in various driving modes
Diagnostics must be carried out comprehensively, since in different driving modes internal hinge behaves differently. On a straight road with uniform movement, a working unit does not make any sounds. The appearance of a hum or vibration at high speeds (usually above 90-100 km/h) may indicate an imbalance or severe wear of the tripod.
When coasting (with the gas released), the knocking, as a rule, disappears. This is a key difference from wheel bearing problems, which hum constantly regardless of whether the engine is turning the wheels or not. If you only hear the sound under the traction, it is almost always the transmission.
Particular attention should be paid to the behavior of the car at start. If you hear a single but loud knock when you start abruptly, this may be a sign that the tripoid is loose in the body. In advanced cases, this blow can vibrate into the car body.
- 🚗 A dull knock during sudden acceleration in any gear.
- 🚗 Body vibration when accelerating.
- 🚗 No sounds when coasting.
- 🚗 Possible jerks during torque transmission.
Another symptom may be an oily stain under the car near the transmission. This indicates that the boot was torn a long time ago, and the lubricant has already leaked out. In that case replacing the inner CV joint is mandatory, since further driving will destroy the mating part on the box.
Diagnostic methods: checking the backlash and condition of the unit
To accurately determine the malfunction, it is not enough to simply listen to the car. It is necessary to drive the car onto a lift or inspection hole. First of all, inspect the anthers. Even if they are intact, if the grease inside looks black and contains metal shavings, this is a sign that destruction has begun.
The main method of checking is to rock the shaft with your hands. Grab the actuator as close to the inner joint as possible and try to wiggle it up and down and sideways. The presence of noticeable play (free play) is a direct confirmation of wear. A functioning hinge should not have any free play.
☑️ Checklist for checking the CV joint
You can also use the rocking method with the engine running (observing safety precautions!). Have an assistant put the gear into gear and lightly press the gas, creating a load. At this moment, with your hand (without getting into the rotating parts!) you can feel the characteristic blows in the hinge body.
| Symptom | Probable Cause | Action |
|---|---|---|
| Crunch when turning | Wear of outer CV joint | Replacing an external grenade |
| Knocking noise when accelerating | Wear of the inner CV joint | Backlash diagnostics, replacement |
| Rumble at speed | Wheel bearing or CV joint | Hearing test at the wheel |
| Vibration during acceleration | Drive imbalance | Checking Shaft Geometry |
Keep in mind that a visual inspection may not show all problems. Sometimes play appears only under a certain load, which is difficult to reproduce by hand. Therefore, a combination of visual inspection and test drive gives the best result.
Consequences of operating a car with a faulty CV joint
Many drivers mistakenly believe that they can drive with a slight knock until it becomes unbearable. This is a dangerous misconception. collapsing tripoid begins to generate metal shavings, which are spread throughout the gearbox, getting into the oil and onto other gears.
At a critical moment, for example, when overtaking or making a sharp maneuver, the shaft may simply jam or fly out of the gearbox. In a front-wheel drive car, this often causes the wheel to lock and the car to lose control. At high speeds, this is almost guaranteed to lead to an accident.
⚠️ Attention: Operating a vehicle with a damaged internal CV joint can lead to damage to the gearbox and differential seal, which will require expensive transmission repairs.
In addition, a tripod falling out of the body can damage suspension elements or even puncture the brake hose. Therefore, when the first signs of a malfunction appear, repairs must be made immediately. Savings on replacing a grenade can result in the purchase of a new gearbox or body repair after an accident.
Is it possible to replace only the internal part?
Theoretically, some manufacturers allow you to change only the inner race (tripoid) without replacing the entire body and shaft. However, in practice, it is difficult to find a high-quality repair kit part, and the seats on the shaft are often already worn out. It is better to change the assembly.
Replacement and selection of spare parts
When choosing a new spare part, it is extremely important to pay attention to the manufacturer. The market is oversaturated with cheap analogues that last only 10-20 thousand kilometers. Original or proven brands like GKN, Lobro, Metelli last many times longer.
The replacement process usually requires removing the entire drive shaft. To do this, the hub nut is unscrewed, the ball joint or stabilizer link is disconnected, and the shaft is knocked out of the hub. Then, using a special puller or gentle blows (through a drift), the internal hinge is knocked off the shaft or disconnected from the box.
When replacing, be sure to use only special lubricant for CV joints (usually molybdenum disulfide-based, black). Regular lithol or graphite lubricant will not withstand high loads and will quickly leak out.
- ✅ Buy a kit with a new boot, clamps and lubricant.
- ✅ Use only specialized lubricant.
- ✅ Check the condition of the response part at the checkpoint.
- ✅ After replacing, be sure to check the oil level in the gearbox.
Tip: When installing new clamps on the boot, use pliers rather than pliers. This will ensure a seal and prevent dirt from entering in the future.
After assembly, it is necessary to check the installation geometry. If the shaft is crooked, vibrations and knocks may return very soon. Also, do not forget to replace the hub nut with a new one if required by your vehicle's regulations.
Main conclusion: A knocking noise during acceleration is almost always an internal CV joint. Ignoring this sound will destroy the transmission and risk an accident.
Frequently asked questions (FAQ)
Is it possible to drive if the inner CV joint is knocking a little?
Strongly not recommended. Even a slight knock indicates the presence of play, which will progress. This is a safety issue: jamming the drive at speed can lead to loss of control.
How much does it cost to replace an inner CV joint?
The price consists of the cost of spare parts and labor. The hinge itself can cost from 3 to 15 thousand rubles, depending on the car model and brand. Replacement work usually takes 1-2 hours of normal time.
Why does the new CV joint knock after replacement?
There may be several reasons: a defective spare part, incorrect installation (not fully seated on the splines), lack of lubrication or damage during installation. It is also worth checking the condition of the shaft and mating part.
How to distinguish a CV joint knock from an engine knock?
Engine knocking usually depends on crankshaft speed and does not change when changing gears at the same speed. The knock of the CV joint is strictly tied to the load on the wheels and the gear: in 3rd gear it will sound differently than in 1st at the same engine speed.