Structurally, the rear suspension of the car is much simpler than the front. However, this does not mean that there is nothing to knock there. A knocking sound in the rear suspension usually becomes heard at the moment when repairs are required. In the front chassis you can feel the feedback on the steering wheel, pedals, body, and the sounds are closer. In the rear, the sounds are transmitted into the trunk, where it is difficult to hear them. And when the driver needs to transport something long and the seats are folded, then the knocking becomes clearly noticeable and the understanding comes that there is a problem. And if the type of knock in the front suspension is not difficult to understand what happened to the car, then in the case of the rear suspension, diagnosis is more difficult. But you can understand the reason.
The easiest and most reliable way to diagnose a knock in the rear suspension is manually, but this is only if it is not possible or you do not want to go to a service station. There are also diagnostic stands that will accurately identify any suspension problems. You shouldn’t drive with knocks, although the rear suspension may not seem particularly important - in the future this can lead to undesirable consequences.
What to check first?
You should start self-diagnosis not with the rear suspension, but with the exhaust system. The exhaust tract should be checked from beginning to end. Very often, the cause of a clunking rear suspension is in the muffler and not somewhere else. To do this, the car is driven into a pit or raised on a lift, and the fasteners and all parts of the exhaust system are carefully checked. Next, pump the exhaust pipe. If it doesn't make any sounds or hit the bottom, then everything is fine and you can move on.
Next, check the trunk. Experts recommend paying special attention to the spare wheel mounting points. An instrument can get into the niche and cause sounds similar to the knocking of a suspension. But if these checks did not yield anything, then you need to move on and diagnose the elements of the rear chassis.
Consequences of ignoring a knock
Any extraneous sounds that appear while driving must be identified without delay, as their presence may indicate a serious malfunction. In this case, let’s look at the consequences of knocking in the rear suspension:
- If problems arise in the guides and are not resolved in a timely manner, in addition to material costs, controllability may deteriorate; in some cases, this malfunction leads to a situation where the suspension is secured only by a spring and a shock absorber. The result is wear and tear of all elements, creating an emergency situation.
- If the spring is damaged, the car sways on uneven roads. In addition, the spring does not limit the movement of the shock absorber. The result of spring wear is terrible stability of the car on the road and damage to other suspension elements.
- Failure of shock absorbers is accompanied by a constant knocking sound. As a result, severe wear occurs on the fastening elements, as well as the shock absorbers themselves. In this case, controllability deteriorates significantly, and strong roll is possible when turning at high speed.
In most cases, a knock in the rear suspension is detected almost immediately, as it occurs while overcoming a bump or pothole on the road. As a rule, suspension elements fail after their service life has expired. If you replace parts in a timely manner, you can avoid road accidents and serious material costs.
Checking the levers
The car is driven into the pit and a gear is installed at the gearbox - in this case it is better not to use the handbrake. For diagnostics you will need a mount. With its help, the serviceability of silent blocks and bushings in the levers is checked. If there is play, then the bushings need to be changed.
The suspension arms need to be checked for integrity. Often these parts become deformed when driving. This can lead to a knocking sound in the rear suspension. Cracks will indicate the need for urgent replacement of the levers. The fasteners of the levers may loosen during driving - if this is the case, then they are tightened.
Deformed levers may knock on the body when driving. Other parts in the rear suspension also make noise. This is determined by the rocking of the car.
This simple diagnostic method by swinging allows you to quickly and without serious costs obtain the most complete information about the condition of the suspension. But you shouldn’t expect a miracle - a car won’t always reveal all its secrets so easily. It happens that you can hear a knock from the rear suspension while driving, but in a pit or at a service station you can’t hear anything.
Diagnostics of suspension guides
Many cars have a similar rear suspension design, which makes diagnostics and dismantling easier. The differences can only be in the principle of fastening and the type of installed parts. During the diagnosis you should:
- We check the force of the beam, if there are levers. As a rule, due to severe wear, cracks appear, which cause deformation.
- If the hinges are too worn, they can also cause a knocking noise from the rear. Cracks may appear on the hinges, which cause their deformation.
The threaded connection of the flanges used when attaching the guide elements can also cause a problem. The flanges can be repaired, but it is recommended to install new ones. The check is carried out on an overpass or pit, since problems are determined visually or using force (that is, you need to strongly loosen the guide elements with your hands). This will require good lighting. Therefore, it is recommended to carry out work in the garage.
Checking racks and supports
If the racks make a strange sound, this can be determined quite simply. When the car is rocked, you need to place the wooden handle of the hammer against the stand and feel if the knock is heard on the object. You may hear deformed or sagging springs. Loose strut mounts can also actually make knocking noises.
There are also problems in the upper mount of the rack. The top mount is broken - this can be seen from the trunk. You need to place your finger on the mount and then rock the car up and down. If the lower fastening has lost its elasticity, this is checked in approximately the same way, but this time on the pit from below - a finger is applied to the fastening from below.
The stand itself may also fail. This is determined when all other options for the appearance of knocking in the rear suspension are excluded. Then you need to change the shock absorber on the car.
Next, check the springs - they can make a variety of sounds. The coils hit each other, there are various problems that lead to spring breakage. To carry out a full diagnosis, you need to disassemble the parts, but this is usually done when nothing else helps. Pay attention to the integrity of the rubber gaskets, which are sometimes installed on the upper and lower parts of the spring from the factory. They smooth out impacts on the body during suspension operation. If there are no such elements, it is likely that the sounds arise precisely because of this.
It often happens that a knock in the rear suspension appears only when driving, but when diagnosed, everything is in perfect order. Then the spring needs to be disassembled.
Spring problem
Although springs are very durable, they can also wear out over time under certain operating conditions. Often, spring wear manifests itself in a slightly different way: the car wobbles at high speed, strong rocking, or a sagging rear end. However, when looking for something that may be knocking, you can conduct a visual inspection and pay attention to the following points:
- Do the turns have any defects?
- Are the rubber pads intact?
In most cases, springs lose their elasticity due to long service life or when exposed to heavy loads (for example, a passenger car has been used for a long time to transport a heavy load). The appearance of defects in the turns indicates poor quality of the metal used in manufacturing, a manufacturing defect, or severe wear. If everything is in order, we carry out further inspection.
Shock absorbers: a common problem caused by rough roads.
Shock absorbers can be considered the most vulnerable structural element. They are designed to absorb impacts when overcoming broken sections of the road. You can determine shock absorber wear as follows:
- Visually - if a clear oil leak appears, as indicated by oil stains, this structural element must be replaced or repaired.
- Completely disassemble the shock absorber. To do this it is necessary to dismantle them. There are rubber bushings inside the shock absorber that often fail. The problem with shock absorbers manifests itself when overcoming bumps. There may also be poor vehicle stability when driving at high speed. It is worth considering that the method is only suitable for serviced shock absorbers.
Brake calipers
This situation is possible on some car models with rear disc brakes. The reason is unscrewing or play in the calipers. This is a common problem for budget car models. It is inexpensive fasteners that often lead to parts failure. Often such knocks are very difficult to diagnose. You will have to perform a whole series of operations.
The first step is to pull the caliper with your hands while the wheel is screwed on. There is a chance that these parts are hitting the brake disc. But everything must be tightly tightened. Then they remove the wheel and carry out manual diagnostics of all caliper fastenings - they pull the mechanism with their hands and check for play.
Next, the caliper is disassembled to identify loose parts. Particular attention should be paid to the quality of tightening of each module and element, each bolt. This may suggest the nature and cause of the knocking noises. You also need to pay attention to the brake pads - perhaps they are worn out or deformed and knock in their place when driving.
In the case of drum brakes, everything is much simpler. None of the elements in this mechanism can provoke knocking. This is only possible when the drum has crumbled. But there is no need to discount the brakes, especially if you hear a knocking sound in the rear suspension when braking. The pads have already been discussed and now we need to look at the situation more deeply.
Other reasons
If diagnostics have been started and no obvious problems have been identified, you can pay attention to the following:
- A brake caliper is an element of the brake system, which, when the pedal is pressed under the influence of the created pressure in the brake hydraulic system (mechanical and electronic are quite rare), compresses the wearing pads. In some cases, misalignment is possible, due to which the pads will wear unevenly and a knock may appear during braking. You can check the caliper visually, as it should also have no defects.
- The hub or bearings are a common problem that leads to humming and knocking noises while driving. To check, the brake disc or drum must be removed. If installed bearings are severely damaged during dismantling, they spill out or have defects that can be identified visually. The bearing mounting method is pressing. That is why, when it gets wedged, the hub can wear out, as evidenced by the bearing turning. You can determine problems with the hub or bearings without dismantling work, for which you need to slightly rock the wheel to the side.
- Another sign is a loose wheel. Wheel rims need to be balanced.
Diagnostics of the vehicle elements listed above in this paragraph should be carried out periodically, since their failure will lead to brake failure or loss of controllability (there are known cases when the hub bursts due to severe overheating, as a result of which the wheel can jam at speed).
What else could be knocking?
There are also the most incredible causes of knocking noises that drivers have been looking for for many years and cannot find. If there is even a slight knock in the rear suspension, it will intensify over time and it can be localized. But it’s worse when this knock doesn’t change. Additional checks are needed.
Often the reason is a wheel that has come loose after a tire service. There may also be metal parts in the trunk that knock two against each other - in the cabin it seems that this is a knock in the suspension. The spare tire may knock against the housing for it. The body itself may also be knocking. And the muffler – it vibrates often.
The service station is the first to check all these reasons. This way you can understand where the rear suspension knocking on small bumps comes from when driving, without even moving on to diagnosing the suspension. You just need to normally look for the reason and have more information on how to solve problems.
Rear suspension design
In order to determine what could be knocking in the suspension, you should know what this element of the car consists of.
- Guide structure.
- Twisted coil springs.
- Shock absorbers.
- Rubber bushings and mounting cups.
A sound in the rear suspension may appear when one of the above elements fails. At the same time, we note that if there is a constant knocking, it is imperative to carry out diagnostics of the suspension. If working with a car causes many problems, then you can entrust the diagnostics to specialists from a car service center. Note that the rear suspension has a very simple design and you can dismantle the worn part yourself.
Possible causes not related to suspension
Before determining what might be knocking, you should make sure that there is a problem with the suspension. Often, a knock may appear due to a minor malfunction of another element, but with strong vibration on the road, it seems that the problem is with the chassis elements. Possible causes of knocking include the following:
- The exhaust pipe in most cases becomes the cause of the knocking, as its fastening wears out over time.
- poorly secured items in the cabin or luggage compartment. You need to check the contents of the trunk, especially the mounting of the spare wheel. If during the first inspection no obvious problems are identified, we proceed to diagnosing the suspension.
Peculiarities
These sounds can have a very different character. They can be heard from different sides of the car, and also occur in a certain position of the pedal. The knock can be either single or repeated. Most often, a knocking noise is heard from the front when braking after any maintenance work has been done on the brake system. It is very difficult to diagnose problems in brake mechanisms by knocking. Even if something vibrates, it is not at all necessary that it will be the brake system. Sounds can come from leaking struts and failed rear shock absorbers, anti-roll bar fasteners and many other components.
