Every owner of a car with all-wheel drive or rear-wheel drive will sooner or later encounter a drive shaft malfunction. This transmission element experiences heavy loads, which is why it needs frequent maintenance.
Consider the peculiarity of the operation of this part, in which nodes the cardan is used, how is it arranged, what are the malfunctions and how to service it?
Cardan is a mechanism that transfers rotation from the gearbox to the rear axle gearbox. The task is complicated by the fact that these two mechanisms are located in different planes with respect to each other. All models of cars, the rear wheels of which are driving, are equipped with cardans.
The transmission cardan is installed along the exhaust system of the car and looks like a long beam going from the gearbox to the rear axle. It is equipped with at least two cross joints (one on each side), and in nodes with a small displacement of the axes - one.
A similar gear is also used in the steering system of a car. A hinge connects the steering column to a steering gear located in a different plane.
In agricultural machinery, such a device is used to connect additional equipment to the tractor power take-off shaft.
The description of the principle of the cardan type transmission was made by the Italian engineer and philosopher J. Cardano. In the automotive industry, this scheme was successfully applied by the industrialist Louis Renault on the modification of the car "De Dion-Bouton" (1898).
The following elements are included in the cardan mechanism.
1. The central shaft. It is made of hollow steel pipe. Void is necessary to facilitate construction. On one side of the pipe there are internal or external slots. They are required to install a sliding fork. The hinge fork is welded on the other side of the pipe.
2. The intermediate shaft. In multi-sectional modifications of the cardan, one or more of these elements are used. They are installed on rear-wheel drive cars to eliminate the vibration that occurs when a long pipe rotates at high speeds. On both sides fixed forks of hinges are fixed on them. In sports cars, one-section driveshafts are installed.
3. The crosspiece. This is an element of the hinge with tips, inside which is located a needle bearing. The part is installed in the eyes of the forks. It transfers rotation from the driving fork to the driven. Additionally, they provide unobstructed rotation of two shafts, the angle of which does not exceed 20 degrees. In the case of a larger difference, another intermediate section is installed.
4. Outboard bearing. It is mounted in an additional section mount. This part fixes and stabilizes the rotation of the countershaft. The number of these bearings is identical to the number of intermediate sections.
5. Sliding fork. It is inserted into the central shaft. When the car is moving, the distance between the bridge and the gearbox is constantly changing due to the shock absorbers. If you fix the pipe tightly, on the very first bump you will need to change some kind of knot (the one that will be the weakest). This may be a break in the shaft mounting or failure of the bridge parts. The sliding fork is equipped with slots. Depending on the modification, it is either inserted into the central shaft (corresponding grooves are made inside it), or is worn on top of the pipe. Slots and grooves are needed so that the pipe rotates the hinge.
6. Hinge forks. They connect the central shaft to the intermediate. The flange plug has a similar shape, only it is installed at the place of attachment of the entire mechanism in front to the gearbox, and at the rear to the axle gearbox.
7. Flexible coupling. This part softens the shock of the universal joint when it is shifted while riding. It is installed between the flange of the output shaft of the box and the plug-flange of the central shaft of the cardan.
The main objective of this mechanism is the transmission of rotational movements on axes located in different planes. The gearbox is located higher than the rear axle of the car. If you install a straight beam, due to the displacement of the axes, it either breaks itself or breaks up the nodes of the box and bridge.
Another reason why this device is necessary is the mobility of the rear axle of the machine. It is fixed on shock absorbers, which move up and down when driving. In this case, the distance between the box and the rear gear is constantly changing. A sliding fork compensates for such differences without loss of torque.
Basically, most motorists associate the concept of cardan transmission with the operation of the rear-wheel drive transmission. In fact, it is used not only in this auto node. The steering and some other mechanisms that connect to neighboring ones at different angles work by a similar principle.
There are 4 types of gears:
- flexible half;
- semi-cardan hard.
The most famous type of cardan gears is asynchronous. The main application is in transmission. It is also called transmission with a hinge of unequal angular velocities. Such a mechanism consists of two forks, which are connected by a cross at a right angle. Tips with a needle bearing allow the crosspiece to move smoothly in accordance with the position of the forks themselves.
This hinge has one feature. It transmits an uneven indicator of torque. That is, the rotation speed of the connected shafts is periodically different (for a full revolution, the secondary shaft overtakes two times and lags behind the main one twice). To compensate for this difference, another hinge is used (on the opposite side of the pipe).
How asynchronous transmission works is shown in the video:
Synchronous transmission is equipped with a constant velocity joint. Owners of cars with front-wheel drive are familiar with this device. A constant velocity joint connects the differential to front wheel hub. Sometimes they are equipped with transmissions of more expensive four-wheel drive cars. Compared to the previous type, synchronous transmission is less noisy, but more expensive to maintain. SHRUS provides the same speed of rotation of two shafts with an angle of inclination of up to 20 degrees.
Flexible half-cardan transmission is designed to rotate two shafts, the angle of which does not exceed 12 degrees.
In the modern automotive industry, rigid semi-cardan transmission is rarely used. In it, the hinge transmits torque when the shaft tilt angle is shifted to two percent.
There is also an indoor and outdoor type of cardan gear. They differ in that the cardans of the first type are placed in the pipe and more often consist of one hinge (used in trucks)
Check the cardan in the following cases:
- during acceleration, additional noise appears;
- an oil leak appeared near the checkpoint;
- knock when shifting gear;
- at speed, increased vibration is transmitted to the body.
Diagnostics must be carried out by lifting the car on a lift or using jacks (for how to choose the appropriate modification, see separate article) It is important that the drive wheels can rotate freely.
Here are the nodes to check.
- Mount. The intermediate support and flange joints must be tightened with a bolt with a lock washer. If it is missing, the nut loosens, resulting in backlash and excessive vibration.
- Elastic coupling. It often fails, since the rubber part compensates for the axial, radial and angular displacements of the parts to be joined. You can check for a malfunction by slowly turning the central shaft (in the direction of rotation and vice versa). The rubber part of the coupling must not be torn or loosen at the place where the bolts are fastened.
- Sliding fork. The free lateral movement in this assembly appears due to the natural wear of the spline joint. If you try to rotate the shaft and the coupling in the opposite direction, and at the same time there is a slight backlash between the fork and the shaft, then this assembly must be replaced.
- A similar procedure is carried out with hinges. A large screwdriver is inserted between the eyes of the forks. It plays the role of a lever, with the help of which they try to crank the shaft in one direction or the other. If backlash is observed during rocking, the cross must be replaced.
- Outboard bearing. Its serviceability can be checked by taking with one hand the shaft in front of it, and with the other - behind it and shaking it in different directions. In this case, the intermediate support must be firmly fixed. If play is noticeable in the bearing, the problem is solved by replacing it.
- Balancing. It is performed if the diagnosis does not reveal any malfunctions. This procedure is performed on a special stand.
Here is another video that shows how to check the gimbal:
According to the recommendations of the manufacturers, the cardan is serviced after 5 thousand kilometers. In this case, it is necessary to check the elastic coupling and crosspieces. If necessary, wear parts are replaced with new ones. Slides of the sliding fork are lubricated.
If a cardan with serviced cross pieces is installed in the machine, they must also be lubricated. This modification is determined by the presence of grease in the universal joints of the cardan (hole for connecting an oil syringe).
Since this mechanism is in constant motion, and it experiences heavy loads, malfunctions are often encountered with it. Here are the most common ones.
- Oil appeared on the cardan shaft. It is necessary to pay attention to the gearbox oil seals. They must be changed periodically due to normal wear and tear. Elastic gaskets lose their properties over time and small gaps appear between the shaft and the gland. If a leak appears in the area of the sliding fork, you need to check the condition of the splines. If they have roughness, then the plug must be replaced.
- Shocks during cardan loads are caused by play on the joints. If the free play appeared in the crosses or in the bearing of the pendant mount, then these parts are replaced with new ones. Vibration may occur due to loosening of the bolted joint. In the event of a frequent occurrence of such a problem, you should check whether the Grover is installed between the nut and the mount. This washer prevents the nut from unscrewing with constant vibration.
- Squeaks when you press the accelerator pedal. Check joints. Due to constant contact with moisture and dirt, the cross may fail. If you ignore the creaks, the crosspiece will jam and the joint will break.
- The most common drive shaft malfunction is vibration. But before proceeding with the repair of the mechanism, you should first check the chassis. Impaired wheel balancing also leads to the appearance of vibration at high speeds. If this effect disappears when shifting and another gear, then the cardan has nothing to do with it. Here are the reasons why vibration can occur in the universal joint:
- malfunction of balancing rings (corrosion or break);
- destruction of crosses;
- damage to the central or intermediate shaft (deformation of the pipe leads to an imbalance of the mechanism);
- incorrectly assembled components of the mechanism.
- Ringing in the pipe. Behind the spline connection inside the pipe there is a cover that prevents grease from entering the shaft. To fix the breakage, the pipe is cut, the lid is welded into place, then the shaft is welded. If after the procedure there was a ringing of a different nature (as if a stone was in the shaft cavity), it means that after welding work there was a large scale. A clipping of lead support may lead to ringing. In this case, the problem is fixed by installing a new cardan.
- Rattle when gear is engaged. Occurs in contact with a car body or exhaust system.
- The ringing of the cardan itself may appear due to a breakdown in the mounting of the mud reflector (if any). It is mounted on an intermediate support to protect the bearing from water and dirt. If it hangs, just weld it by welding.
If there is a need to replace the cardan mechanism or repair its assembly, it will need to be removed. The procedure is carried out in the following sequence:
- unscrewing mounting bolts from the rear axle and propeller shaft flanges;
- the shaft goes down;
- bolts of the rubber coupling are unscrewed;
- the cardan moves away from the checkpoint;
- pendant mount is unscrewed.
A repaired or new mechanism is installed in the reverse order: suspension, coupling, bridge flanges.
In an additional video, some more subtleties of removing and installing the cardan are mentioned:
Cardan in the car is a fairly hardy mechanism, but it also needs periodic maintenance. The driver needs to be attentive to the appearance of extraneous sounds and vibrations. Ignoring these problems will break important transmission elements.