Universal joints and gay joints
Axes with a kink do not work. That is why flexible couplings have been devised. For the drive shaft of a clock, this can be a vulcanized piece of rubber. But for serious work there are universal joints and gay joints.
An uneven loop
The universal joints make it possible to transmit a torque at an angle. Universal joints can transfer angles up to 20˚. A major disadvantage of the universal joint is that these malfunctions are caused in the driven shaft. This unevenness is caused by the tilting of the crosspiece during the rotation. That is a fairly complicated story with uneven angular speeds. It means that the shaft behind the coupling rotates at a non-constant speed. Incidentally, that can be solved by adding an 90 degree twisted universal joint. But with technical delights such as the Russian M72s, the builders apparently accepted the disagreement. There is only 1 universal joint in the cardan. And no Russians driver has ever been bothered by that. But of course it could be better.
The CV joint
And a CV joint is the smart brother of the common fork joint. A homokinetic coupling is a universal coupling that is constructed in such a way that it transmits the rotation uniformly. This is possible because the balls which transfer the forces, when the coupling is brought at an angle, come to be at the same distance from the center line of each other. The output shaft remains at a constant speed. And with front-wheel drivers (and sometimes in the cardan of motorcycles) such a thing can go wrong. Or seem to be broken.
Broken or not broken?
If the universal joint (CV joint) with front-wheel drive is worn out, this often results in a thumping sound. If the drive shaft is very bad, it is fairly easy to determine the clearance. But in the initial phase there can be a lot of doubt whether it is actually the drive shaft that you hear. The coupling (CV joint) is located under a dust cover. This cover is to protect the coupling that is lubricated by special joint grease against dirt and moisture from outside. This cover also ensures that the fat stays inside the cover. If these dust covers become hard over time due to weather influences, they can crack and have to be replaced.
False alarm
It also happens that when the covers become hard, they make a lot of noise. So much noise that you soon think that the shaft (CV joint) itself causes the sound. By greasing the cover on the outside with grease or vaseline the problem is solved. If the cover needs to be replaced, this is very difficult without special tools. The narrow opening of the cover must first slide over the CV joint. The sleeve must be fitted with the appropriate clips after it has been filled with special CV joint grease. If there is too much grease on the edge of the dust cover when mounting, it is useful to use brake cleaner for this.
Oh yes: one pounding, grinding, crackling noise can also be caused by mounting rubbers. A sturdy shower with WD 40 would often do wonders there.
