The intermediate support 3 of the rear end of the front shaft 2 is elastic with a ball bearing. It is attached to the cross member of the body. The middle cardan joint is universal.
The presence of two short cardan shafts reduces the likelihood of vibration due to imbalance. Two short shafts with an intermediate support are less susceptible to damage, and the supports experience significantly less load. But, despite the listed advantages, a number of malfunctions still occur during operation, due to which the cardan transmission units and parts must either be repaired or replaced.
Knocking in the cardan transmission
After about 50-60 thousand km of mileage, it may happen that the cardan transmission will start to make a knocking noise, and it will occur when starting off, accelerating sharply or changing gears.
The reasons for knocking may be:
- loosening of bolts and nuts of the elastic coupling and cardan joint flanges. The defect occurs because the owner ignored the recommendations and did not control the quality of the fastening of the transmission units and assemblies for a long time;
- increased clearance in the splined joint of the cardan shafts;
- increased clearance in the cardan shaft bearings.
If the knocking sound of the cardan transmission is caused by one of the last two, then the cardan transmission must be removed, disassembled if possible, and worn parts replaced. To remove the cardan transmission, you need an inspection pit or overpass. The car is installed and fixed in place in the same way as when removing the gearbox or clutch. Work on removing the cardan transmission must be performed in the following sequence:
- remove the safety bracket;
- compress the elastic coupling with a device that is an ordinary clamp (this was mentioned when describing the clutch removal), and, turning the shaft, unscrew the nuts of the bolts securing the flange of the elastic coupling, remove the bolts and the clamp;
- disconnect the rear propeller shaft from the main gear pinion flange;
- disconnect the release spring of the rear parking brake cable guide;
- disconnect crossbar 7 (see fig. 55) intermediate support 3 from the body floor and remove the cardan transmission towards the front of the vehicle.
The removed cardan transmission must first be washed and cleaned of dirt, and only then proceed to inspect the condition of its individual components and parts.
First, check the cardan joints. They should rotate easily and smoothly and not have large axial and radial gaps. It would be good to check the balance of the cardan transmission, but this is difficult to do at home. The cardan transmission is still considered to be quite functional if the imbalance does not exceed 0.0022 N·m (for reference), the forks rotate smoothly, without jamming, the circumferential clearance in the splined connection does not exceed 0.30 mm and grease is not ejected through the seals.
The most common problem is the crosspieces 11 (see fig. 55). As a result of wear of the crosspiece pins and bearings 9, the gap between them increases and the cardan transmission begins to rattle.
As in the case of the camshaft, the problem with the universal joint crosspiece has aroused increased interest among inquisitive car enthusiasts. As a result, it was found that premature wear of the crosspiece studs and bearings, in addition to the traditional reason - dirt ingress, is facilitated by an increased gap between the corners (fig. 56, a). The increased clearance allows the needles to operate at an angle, which is why the crosspiece pins have longitudinal grooves located at an angle to the axis (fig. 56, b).
To eliminate the distortion, some car enthusiasts, having selected from among sewing needles one whose diameter corresponds to the gap between the needles, made from it (cut to size) additional element and filled the gap with it. The result was positive (fig. 56, in), i.e. the traces of wear have evened out.
Just a few years ago, few people dared to change the universal joints themselves. Now this is far from the most difficult operation for a car enthusiast. Certain difficulties in performing this operation are that it is very difficult to balance the cardan transmission at home, so it is necessary to take all possible measures to avoid disturbing the balance. For this purpose, before disassembling, the relative position of the parts relative to each other is marked so that when reassembling they take the original position in which balancing was carried out. It should be noted that even the smallest and lightest parts can disturb the balance. That is why, when replacing the universal joint, even the retaining rings are marked 8 (see fig. 55) and clips 10, where the seals are. In order to remove the crosspiece, the front cardan shaft is installed in a vice and special pliers (they have thin and long lips) remove the previously marked retaining rings 8.
The bearing housings are installed in the forks 12 with tension, so to press them out you need to use either a clamp or a hammer and a punch.
The device (Fig. 57), suggested by a car enthusiast from Baranovichi, allows you to disassemble and assemble the crosspiece in just a few minutes, without even completely removing the cardan shaft from the car. To perform this operation, you need to:
- disconnect the propeller shaft from the rear axle gearbox flange and remove all lock washers from the crosspiece;
- put on a ring (fig. 57, a) with bushings screwed into it (fig. 57, b) on the cardan joint;
- bring the bushings to the forks into which the crosspiece bearing housings are pressed;
- screw the pins into two opposite holes of the bushings (fig. 57, in) until it stops at the bottoms of the crosspiece bearings.
Having completed these operations, you have securely fixed the device on the cardan shaft. Now all that remains is to press out the crosspiece by rotating the two bushings of the device with a 32 mm key.
Before assembling the joint, first of all, fill the cavities in the crosspiece tenons and lubricate the inner surface of the bearing housings with Fiol-1 grease (0.4-0.6 g), and then insert the tenons into the fork. The bearing housings together with the needles are put on the crosspiece tenons and pressed in. The defect can be considered eliminated if the axial free play of the crosspiece is practically not felt, since according to the instructions it should not exceed 0.01-0.04 mm. In the event that the gap is too large, you can try to reduce it by installing a thicker retaining ring.
When the knock of the cardan transmission is caused by a large circumferential gap in the splined connection of the forks with the shaft (the gap should not exceed 0.30 mm), the cardan transmission has to be completely disassembled and the worn parts replaced. Considering that these can be forks and even shafts, it is advisable to entrust the repair work to specialists, since special equipment is required and, most importantly, after assembly, the cardan transmission will need to be balanced without fail.
Experience shows that the cardan joints of all-terrain vehicles are in a particularly difficult situation VAZ-2121 "Niva". This is caused by a number of reasons: firstly, this car is designed for driving where the asphalt ends, secondly, the load on the joints, despite the shortened length of the cardan shafts, is significantly greater.
Taking into account the accumulated experience, the plant began to develop cardan joints with bearings of improved design, double seals and grease nipples for periodic filling and renewal of lubricant.
Noise and vibration
Noise and vibration of the cardan transmission usually occur at a speed of 80-90 km/h. The entire car is covered by a small tremor and a monotonous hum is heard. It has long been known that vibration and the accompanying hum are the result of an imbalance in the cardan transmission, which, in turn, is a consequence of the deformation of one of the shafts, an increase in gaps or a weakening of the support fastening.
It happens that a stone that has flown out from under the wheel at the wrong time hits one of the driveshafts. This is enough to cause an imbalance. It is impossible to drive with a vibrating driveshaft, and it usually has to be replaced.
Noise and vibration may appear after poorly executed assembly work, i.e. due to misalignment of assembly marks. In this case, everything has to be started from the beginning.
Vibration can be caused by increased clearance in the intermediate support bearing. There is no way to get rid of this defect except by replacing the bearing. In any of the above cases, it is advisable to contact a service station, as balancing will definitely be required.
Rarely, but it is possible that the vibration is caused by a loose crossbar mount to the car body. If this is indeed the cause, it can be easily eliminated by tightening the crossbar mount nuts.