4.4.2. Definition of a source of vibrations

Definition of a source of vibrations also is diagnostics element, however it is not systematized. Vibrations are transmitted through a suspension bracket and further through a rotary fist (the center of rotation). Then their "way" (or "transfer function") depends on energy of vibrations, the nature of communications between details (inhalings of fastenings, conditions of the vibroextinguishing elements, etc.), their rigidity or on various possible components of the impulses causing vibrations.
It is possible to assume that in most cases transfers of vibrations on a steering wheel they proceed from a forward suspension bracket and are transmitted through steering. But also it is not absolutely universal rule. Some very specific defects of tires of back wheels can be the cause of vibrations of a steering wheel.
Vibrations are caused by the sequence of impulses (blows) going from the elements rotating together with a wheel. Vibrations are caused by the reasons of two types:
– weight imbalance;
– one impulse on a wheel turn.
Forward and back suspension brackets possess characteristics on the basis of which diagnostics is carried out.
They extinguish vibrations, except those which have the frequency of "own fluctuations".
The moment of emergence of own fluctuations of a suspension bracket depends on its longitudinal rigidity. Frequency of fluctuations is caused by the speed of the movement of the car. The moments of emergence of own fluctuations of forward and back suspension brackets differ one from another.
Diagnostics of vibrations allows to define from what suspension bracket (forward or back) they proceed, and, in particular, to define number of impulses for a wheel turn. These basic diagnostic data serve as a reference point for the choice of necessary technical intervention. Therefore it is important to obtain these data from the owner or to execute road test.
The imbalance size necessary for creation of notable vibrations makes near:
– 20 g for wheels (the tire on a 15-inch disk);
– 100 g for a brake disk or a drum;
– 500 g for a wheel nave;
– 1,16 kg for a wheel drive shaft.

Some types of the vibrations caused by operation of the engine can be taken for the vibrations connected with the speed of the movement. In this case emergence of vibration is connected most likely with turns or loading of the engine. Only reproduction of malfunction at the corresponding check allows to be convinced of it.