Regardless of which part the silent block is intended for, it has three tasks:
reliable fastening of suspension elements;
maintaining its mobility;
absorption of mechanical vibration.
The latter occurs as a result of wheels hitting the road surface. Let's consider the design features of silent blocks and their service life.
How a silent block works
Let's give an example on a suspension arm, which has a seat for a silent block. The latter is pressed in there, contacting the arm with its outer tube. The arm, in turn, is attached to the car body with a bolt that passes through the inner tube. Thus, vibration coming from the arm passes through the outer tube, not reaching the inner one, as it is absorbed by the damping insert. To make everything work without vibration and knocking, it is necessary to correctly select silent blocks by size so that there is no play.
The damping insert is a rubber or polyurethane bushing. The former has a low cost, good elasticity, and sufficient resilience to prevent play between parts. Polyurethane silent blocks have the same properties, but due to higher resilience, they last longer. Accordingly, their cost is higher. In most cases, cars are equipped with silent blocks with rubber inserts at the factory, as they are cheaper and fully perform their functions, albeit not as long as polyurethane ones.
How long do rubber and polyurethane silent blocks last
Replacement of these parts is carried out as they wear out. It is characterized by the appearance of cracks and delamination of the material. As a result, play appears in the connection of parts, and hence knocking and other problems with the car's suspension. As for the service life, a set of rubber silent blocks is recommended to be replaced every 100 thousand kilometers. Under normal conditions, they can last longer, but their properties noticeably deteriorate by this mileage, so it is better to replace them. If the car is operated off-road, the load on the rubber-metal hinges increases, so it is recommended to replace them every 50 thousand kilometers. Polyurethane ones have a service life 2-3 times longer.
When it is necessary to buy silent blocks
You cannot rely only on the manufacturer's recommendations, so you should monitor the condition of the rubber-metal hinges. You can determine that it is time to buy silent blocks by their appearance. If they are covered with microcracks or deformed, replacement is necessary. You can understand that they are worn without looking under the car by the following signs:
The car's handling has deteriorated.
Strong vibration appeared in the cabin while driving.
The suspension began to make extraneous sounds.
The car's braking distance has increased.
The vehicle's directional stability has worsened.
It has become harder to control the car.
The wheels' response to steering wheel turns has worsened.
Not in all the above cases will you have to buy silent blocks, because many signs also mean other problems with the car's suspension. You can finally make sure of the need to replace silent blocks only by visual inspection or by diagnostics on a special stand in a car service center. It is recommended to entrust the replacement to service station masters, since incorrectly installed rubber-metal hinges will negatively affect the car's suspension operation.
