Silent blocks are a rubber-metal sleeve designed to absorb and eliminate vibrations and shocks caused by vibrations of mechanical elements, e.g. in the suspension, while driving a car.
How are they built?
The silent block consists of a metal structure made of two sleeves inserted into each other. Between the sleeves there is an elastic part (rubber element) responsible for dampening vibrations and absorbing vibrations.
Silentblock – application
Silentblock is a rubber combined with a metal insulator, thanks to which you can reduce vibrations. It is mainly used for:
- connecting parts of the car suspension
- leveling vibrations transferred from one element to another
- installation in various vehicle systems (engine, gearbox, shock absorbers)
- mitigating vibrations of internal fans, washing machines, cylinders, motors
- leveling the transmission of vibrations to the outside
- easing and resolving loads occurring in vibrating and oscillating systems
They are used in suspension systems in the automotive industry (suspensions for passenger cars and vans, agricultural machinery, trailers, motorcycles). Their price depends on the material they are made of, as well as their diameter and length. These rubber-metal joints are highly flexible and will be used not only in car suspensions, but also in household appliances and machines.
What are Silent blocks made of?
Rubber-metal sleeves are most often cylindrical or conical in shape. They differ in diameter and length. However, all of them are designed in such a way as to absorb shocks and isolate vibrations. Vibrations transferred from one part to another can cause, among other things, fatigue cracking. Silent blocks can be made of natural and synthetic rubber. The former is characterized by high flexibility and excellent tensile strength. The use of synthetic rubber for the production of bushings makes them more resistant to oil and works in a wider temperature range. The synthetic rubbers of which Silentblocks are most often made include nitrile rubber (NBR) and styrene-butadiene rubber (SBR). Compared to natural rubber (NR), nitrile rubber shows better oil resistance and greater abrasion resistance. Natural rubber (NR) is a material with a hardness of 55 ShA (Shore A scale). Synthetic rubbers (NBR, SBR, EPDM) can be of variable hardness. Styrene-butadiene rubber (SBR), compared to the natural one, shows greater resistance to thermal aging and is characterized by greater resistance to loads and shocks. The advantage of natural rubber in rubber-metal bushings is high tensile strength, tearing and tearing strength, as well as very good resistance to low temperatures, reaching – 50 ºC. The standard material from which the metal part of the sleeve is made is galvanized steel. Galvanization prevents, among others the presence of corrosion centers. On the sleeve packaging you will find a lot of information about the size, diameter and material of which it is made. The price of the product also depends on these parameters.
The finished product consists of two connected sleeves with a rubber bonded between them. Natural or synthetic rubber is injected into the gap between the two bushings to fill the void between them. Then the rubber is vulcanized. Vulcanization (cross-linking process) is one of the steps in the formation of rubber-metal sleeves, resulting in a flexible rubber that exhibits better resistance to abrasion or temperature fluctuations. Then, the silenblocks are pre-compressed, which increases their dynamic strength and service life. There are also offers on the market for sleeves made of polyurethane, the price of which differs from rubber-metal elements.
Worn Silentblock – How to replace?
Due to the stresses imposed on metal-rubber bushings, their wear should be monitored regularly. A control arm silentblock (eg Febi Bilstein) is fitted to soften vibrations and to reduce excessive noise generated by the suspension while driving the car. Increased wear occurs most often when driving over uneven surfaces. A worn-out control arm Silentblock reduces driving comfort and has a negative effect on the suspension.
Signs of wear of the bushing
The following symptoms may indicate that the sleeves require replacement:
- characteristic knocking or creaking near the chassis
- faster tire tread wear on the side of the damaged shock absorber
- jerking when starting the vehicle or braking
- wheel alignment problems
- rocking the vehicle or the wheels losing contact with the ground
- difficult to keep track
If, when checking the condition of the rubber shock absorbers, it turns out that they are cracked or peeling, also replace them with new ones.
How to replace the control arm silentblock?
Silent blocks are a very important component of fastening the car’s chassis. After the diagnosis, for safety reasons, it is recommended that the shock absorber is replaced in pairs on both sides. The replacement of the control arm silentblock (eg Febi Bilstein) is most often commissioned to specialists in a car repair shop (the price of the service differs in many cities). However, if you have a hydraulic press and know how to repair or replace worn parts in cars, you can take on the task yourself. First, the control arm must be disassembled. Old and worn bushings are pushed out with a hydraulic press. In order to facilitate the assembly of new Silnet blocks, it should be lubricated with grease. To avoid damaging the control arm, be careful during these steps. Once the control arm silentblock is in place, align the wheel alignment so that the wheel path is aligned with its axis. There are many types of sleeves on the market in various shapes and sizes. This means that the correct assembly of each Silentblock may be slightly different. You can have an influence on ensuring the proper durability and the operation of the bushing pay attention to its correct assembly. An improperly pressed-in sleeve can have a negative effect on the rest of the fastening system, causing excessive wear or damage. A properly installed set of rubber-metal sleeves ensures safety, ensuring, among others, maintaining the track and proper damping of shocks and isolation of vibrations. The data provided by the manufacturer provides a lot of necessary information regarding the size, shape, diameter, material used and the possibilities of applications in individual vehicles.