What is the silent block and when it is changed

Silent blocks (hereinafter referred to as “s / b”) are a suspension part, which is two metal bushings, between which there is a rubber insert. The silent block connects the suspension parts to each other, dampens vibrations between the nodes. Silent blocks contribute to a comfortable ride due to the elasticity of the rubber, which serves as a damper between the suspension parts. 

What is the silent block and its purpose

Silent blocks work to avoid deformation of suspension parts and bodywork. They are the first to take shocks and vibrations, after which they are damped by shock absorbers. Also silent blocks are divided into the following categories:

• design (with one, two bushings or without metal elements);
• design load (continuous elastic insert or with holes);
• type of fastening (bushings or case with eyes);
• mobility (medium mobility and “floating”);
• material (rubber or polyurethane).

Structurally, silent blocks differ in shape, depending on the design of the lever. Most often, two bushings are used on triangular levers of the MacPherson type front suspension - rear silent blocks with two bushings, front ones with an inner bolt, there is no outer clip. By the way, the rear s/b of the front suspension can be hydrofilled. This design allows you to better absorb the vibration energy, but as soon as the liquid begins to flow out, the efficiency of silent blocks decreases sharply.

According to the design load, it is better to use continuous s / b, their resource is much higher.

In terms of mobility, “floating” silent blocks are worth special attention. They are used in the rear multi-link suspension, they can be pressed into the steering knuckle or transverse rod. The “floating” hub has a second task - to allow the wheel to turn freely at a certain angle, while remaining motionless in the vertical and horizontal plane. The product is a cage, closed on both sides with anther, inside of which a hinge is installed. Due to the movement of the hinge, the rear suspension “steers” when necessary, the car on the road is more stable in sharp turns due to this .. The main disadvantage of the “floating” bushing is that that the rubber boot is too vulnerable to an aggressive environment, after which it passes dust and moisture, sharply reducing the life of the part. 

Where are the silent blocks located?

Rubber-metal bushings are used in the following suspension parts:

• front and rear levers;
• longitudinal and transverse traction of the rear suspension;
• as stabilizer bushings;
• in turning fists;
• in shock absorbers;
• as a fastening of the power unit and transmission;
• on stretchers.

The use of full-fledged silent blocks instead of rubber bushings significantly improved the technical characteristics of the chassis due to the fact that the rubber in the rigid sleeve works better for twisting, dampens vibrations more efficiently and does not wear out so quickly. 

Types and types of silent blocks

There are two categories by which all silent blocks are classified:

• By the material from which they are made;
• By type (shape and design).

The bushings for the rear beam and front control arms are made of rubber or polyurethane.

By type they are distinguished:

• Standard non-collapsible. Such parts have a metal cage with a rubber insert inside. There are also modifications with one metal insert. In this case, it will be placed inside the rubber base.
• Perforated silent block or with cavities in the rubber part. Such silent blocks provide smooth twisting of the lever. The part must be pressed in evenly so that the load is distributed over the entire working part of the element.
• Silent block with asymmetric lugs. Such parts do not have a through mounting hole. Instead, lugs are used. This design allows you to fix parts that are in offset planes relative to each other.
• Floating design. Externally, floating silent blocks are similar to ball bearings. So that during operation the rubber part does not wear out, it is covered with a rubber boot. This modification provides a smooth movement of the part mounted on it. They can be used for levers, but more often they are installed in the steering knuckles of the hub.

How to check silent blocks?

The average resource of rubber-metal suspension parts is 100 km. S / b diagnostics is carried out every 000 km. To do this, you need to raise the car on a lift. The primary inspection is visual, it is required to identify the presence of cracks or ruptures of rubber. If there are cracks, then this is a sign that the s / b will need to be replaced soon.

Further verification is carried out using a mount. Resting on the lever, we simulate its operation, while the lever stroke should be tight. This also applies to engine mounts, shock absorber bushings.

On the go, the wear of silent blocks is evidenced by a strong knock on irregularities, the “slackness” of the suspension.

When they change

Silent blocks are replaced only with obvious wear, in other cases it makes no sense to touch them. It is strongly recommended that you change the rubber-metal part from two sides, because on the move the suspension begins to manifest itself inadequately due to the difference in the operation of the levers. 

By the way, not every suspension starts to "sound" when the s / w is worn. For example: the car Mercedes-Benz W210 and BMW 7-series E38 to the last remain “silence”, even when the silent blocks are completely torn. This suggests that running gear should be diagnosed based on mileage and the first signs of inadequate suspension behavior.

Lifetime

Typically, the resource of original components reaches 100 km or more, depending on where the car is operated. Speaking of analogues, the cheapest options may fail already at the second thousand kilometers. The normal mileage of a good analog is 000-50% of the resource of the original spare part. 

How to change silent blocks correctly

The complexity of the procedure for replacing silent blocks depends on the model of the car, more precisely on the type of suspension of the car. But even in the simplest design, silent blocks are not always easy to replace.

Here is a step-by-step instruction for the sequence of this work:

1. Pick the right tools. To hang the car, you will need a jack (if it is not yet in the motorist's toolkit, then in a separate article details how to choose it for your car). You will also need a standard set of wrenches. To make it easier to correctly install silent blocks, it is better to purchase a tool for pressing them on the market. In addition, you will need a special puller for ball joints.
2. Raise one side of the car and remove the suspended wheel.
3. Unscrew and remove the nut on top of the ball joint.
4. The suspension arm is unscrewed.
5. The silent block is pressed out and a new one is pressed in.
6. The lever is mounted. Lubrication is added so that the joint does not wear out faster.
7. The same procedure is carried out with the lower arm.
8. The wheel is baited, and it is already tightened on the ground.

If in the car the rear part of the suspension is equipped with silent blocks, then they are replaced in a similar sequence:

• The back of the car is hanging out.
• The condition of the silent blocks and the presence of play in the levers are checked.
• The rear silent blocks are changed if there are backlashes in the levers or the rubber part of the parts is clearly worn out (there are deformations or cracks).

The rest of the silent blocks on the rear axle are changed in the same way as in the front. The wheels are clamped when the machine is already on the ground to prevent the vehicle from slipping off the jack.

When replacing silent blocks, the suspension geometry is always violated, since the levers and ball bearings are unscrewed. For this reason, after performing repair work, it is imperative to adjust the alignment. Here the importance of this procedure is described in detail.

Which silent blocks are better: polyurethane or rubber?

Definitely, in the event of a silent block failure, a reasonable solution would be to replace it with an identical one, which was provided by the manufacturer. If the driver is unfamiliar with the device of his car, then the selection of silent blocks can be carried out according to the catalog for a specific car.

Before replacing the silent blocks, the car owner should decide on the material from which the part is made.

In the modern auto parts market, the buyer is offered two options: rubber and polyurethane analogues. Here's the difference.

Rubber silent blocks

At the heart of such silent blocks, rubber is used. These parts are cheap and easier to find in stores. But this option has several significant disadvantages:

• Small working resource;
• Creak, even after replacement;
• They do not tolerate aggressive environmental influences, for example, rubber cracks under loads in severe frost.

Polyurethane silent blocks

The most significant drawback of polyurethane silent blocks compared to the previous version is the high cost. However, this factor is overridden by the presence of many advantages:

• Silent work;
• The car's behavior on the road becomes softer;
• The fulcrum is not excessively deformed;
• Increased working life (sometimes up to 5 times when compared with a rubber analogue);
• It dampens vibrations better;
• Improves vehicle handling.

Reasons for failure and what breaks down in the silent block

Basically, the resource of any car part is affected not only by its quality, but also by the operating conditions. It so happens that a high-quality silent block does not deplete its resource in a car that constantly drives on a bumpy road.

In another case, the car is used mostly in the city, and the driver drives accurately and measuredly. In such situations, even a budget silent block can waste a decent resource.

The main breakdown of silent blocks is rupture or deformation of the rubber part, because it is a damper for the fulcrum. Twisting forces act on it at some nodes. Breakage of the metal clip is very rare. The main reason for this is a violation of the pressing procedure.

The rubber part wears out prematurely in the following cases:

• Violation of the technology for replacing silent blocks. When the mounting bolts are tightened, the vehicle should be firmly on its wheels and not jacked up. Otherwise, an incorrectly tightened part will twist after the machine is lowered to the ground. Subsequently, the rubber will break under additional load.
• Violation of the pressing process. If the part is installed with an offset, during operation the load will not be evenly distributed.
• Natural wear and tear. Some drivers pay attention to silent blocks only when there is a problem with them, often exceeding the recommended service life.
• Aggressive exposure to chemicals. This is the reason for the reagents that are poured over the road. Ordinary engine oil also breaks down rubber with ease.

Here are the signs by which you can determine that the silent blocks need to be replaced:

• The car drove almost 100 kilometers (if the road conditions were of poor quality, then the replacement interval decreases - after about 000-50 thousand);
• Backlash appears, the car becomes unstable and less comfortable to drive;
• The tire tread pattern wears out unevenly (it should be borne in mind that this may be the result of other malfunctions, which are described in separate article);
• The arm mountings are damaged.

Carrying out timely and high-quality maintenance of the car, the owner of the car will avoid unnecessary waste on the repair of parts that have not yet arrived.

Video: "Types and replacement of silent blocks"

This video discusses different types of silent blocks and the sequence of their replacement:

Replacement of silent blocks. Types of silent blocks

Questions and answers:

What happens if the silent blocks are not changed? Due to the exploded silent block, the suspension arm becomes crooked. Due to the increased backlash, the hinge mounting seat is broken, which will lead to breakage of the entire lever.

ЧWhat does the silent block do? First of all, these elements connect the suspension parts of the car. During movement, vibrations occur between these parts. The silent block softens these vibrations.

Why is the silent block called? From the English silent block - a quiet knot. It is a non-separable element with two bushings connected by vulcanization.

What are the front arm bushings for? Since there is a soft material (rubber or silicone) in the design of the silent block, then, by connecting the suspension parts, it dampens vibrations and shocks that occur in the levers.