Many car owners are wondering where exactly they are. doorstepEspecially when it comes to the correct installation of jack equipment or diagnosing the body for corrosion. Visually, this area seems obvious - it is the lower part of the doorway, but the structural element is a complex cavity hidden from the eyes by surface plastic or paint. Understanding the exact geometry of this part is critical not only for safely lifting a car, but also for assessing its technical condition before buying.
A modern car is a complex engineering complex, where each bearing part performs the role of a safety element. Longerons And the rapids form a force frame that must withstand enormous loads in lateral impact. If you don’t know where the decorative pad ends and the metal begins, you risk damaging the bodywork with careless maintenance or missing the start of the devastating rust process, which often starts from the inside out.
In this article, we will examine in detail the anatomy of the lower part of the body, learn to distinguish between external linings and internal amplifiers, and discuss methods for checking hidden cavities. Security The durability of your vehicle depends on how well you learn its design. Do not rely only on external inspection, because the problems are often hidden under layers of anticores and factory paint.
Anatomy of the lower belt of the body: external and internal elements
To understand where to look for thresholds, it is necessary to divide the concept into two components: the visible part and the hidden force element. The exterior we see daily is often a plastic lining or painted metal, which is just a decorative screen. Underneath it, the main load-bearing - boxed structure running along the entire bottom of the car from the front wheel to the rear.
It is the inner part of the threshold that takes the main load in a side collision, protecting passengers in the cabin. Structurally, this is a closed profile, access to which is limited by technological holes. In some models, especially in the old ones. VAZ or classic foreign cars, the outer part could be removable, but in modern cars it is a monolithic welded structure. The destruction of this element leads to the loss of geometric rigidity of the entire body.
⚠️ Warning: Never use rapids as a mounting point for a jack unless they have special factory notches or cutouts. The pressure of the jack rod on the thin metal of the outer skin will lead to instant deformation and rupture of the metal.
It is also important to distinguish between the connection zones. Threshold docks with centre-stall The body and the front/back sparser. These welding sites are critical stress points. When diagnosing a car, special attention should be paid to the joints, since there are most often microcracks or foci of corrosion, which over time can lead to serious structural problems.
Why are the thresholds hollow?
The cavity inside the threshold is not only necessary to reduce the weight of the structure. It serves as a channel for laying electrical wiring harnesses, fuel and brake tubes, and also plays a role in the ventilation system of the cabin, ensuring air circulation in the lower layers of the body.
Risk zones: where corrosion occurs most often
The search for rust should begin at the places where moisture and reagents linger the longest. Traditionally. corrosion It attacks rapids in the lower part, where dirt, sand and salt accumulate from the roads. Particularly vulnerable areas behind the front and rear wheel arches, as it is there that the abrasive mixture from rotating tires flies. Here, the coating layer thins the fastest.
The second danger zone is the junction of the threshold with the doorway. In this place, condensation often accumulates, which flows down the glass and the door map down. If the drainage holes at the bottom of the door are clogged, water pours over to the threshold and stays there, causing the metal to rot from the inside out. Checking these areas requires removing rubber seals or using an endoscope.
- 🔍 The lower edge of the threshold is a zone of constant contact with stones and salt, requires regular washing and anticory treatment.
- 🔍 The joint with the central rack is the place where the moisture flowing from the roof and windows is concentrated, often hidden under plastic linings.
- 🔍 Area under a plastic body kit – if the car has decorative linings, under them can form a “greenhouse effect”, accelerating rotting.
Hidden corrosion is the most insidious enemy. It can develop inside the cavity of the threshold, when only a small swollen bubble of paint comes out. When you press your finger in such a place, the metal can fall through. Use of the magnetic-indicator The thickness of the coating helps to identify places where the metal is replaced by a putty, hiding through holes.
Use a conventional magnet wrapped in a thin fabric to quickly check the thickness of the LCP. If the magnet does not hold or holds very weakly, it is likely that the layer of putty in this place is too large, which hides the defects of the metal.
The jack installation points: how not to damage the car
The question of where the doorsteps are often raised when the wheel is replaced. The manufacturer always provides special places for installing jack equipment so as not to damage the power structure. Usually these points are located on reinforced sections of the threshold, closer to the wheel arches, and have characteristic cutouts or rectangular platforms.
If you install the jack incorrectly, for example, in the middle of the span between the wheels, the thin metal of the outer panel will be doubted by the accordion. Restoring geometry after such an incident requires expensive body repairs with digestion of sections. Therefore, knowing the exact location reinforced zones A skill that is mandatory for every driver.
☑️ Check before lifting the car
On some modern models with plastic body kits, the elevation points can be hidden. In such cases, the operating instructions should be carefully examined (Owner's Manual) where the nesting position is schematically shown. Sometimes to access them, you need to remove part of the plastic apron or use special adapters for the jack, which distribute the load.
Methods of diagnosing the state of thresholds when buying a car
When buying a used car, checking the thresholds becomes a key stage of the assessment. The buyer should pay attention not only to the presence of rust, but also to traces of repair. Digested sills are often given out by an unnaturally smooth welding line, differences in the shade of paint or the presence of a sealant in the wrong places. Factory welding It always looks neat and even.
For deep diagnosis, professionals use a thickness meter, but a visual inspection can give a lot of information. Pay attention to the color of the metal in the doorways - it should coincide in hue and structure with other parts of the body. The variety or the presence of traces of grinding indicates that the bodywork was carried out.
| Method of verification | What we looking for | Sign of a problem |
|---|---|---|
| Visual examination | Bloating paint, bubbles | Hidden corrosion under the LCP layer |
| Tactile testing | Metal softness under pressure | Through rust, loss of strength |
| Inspection from below. | Status of spars and bottoms | Deep pockets of corrosion, holes |
| Magnetic test | Attraction force | A large layer of putty, hiding the defect |
Particular attention should be paid to the interior of the doorway. Remove the rubber door seal in several places. Underneath it often hides the boundary between the whole metal and the digested piece. If you see a discontinuous welding line or a sharp drop in the thickness of the metal, this is a sure sign that the thresholds have changed.
Recovery and Protection: Modern Materials
If the diagnosis has revealed problems, it is necessary to start recovery. Modern industry offers many solutions for protection metalwork. The most effective method is considered to be complex anti-corrosion treatment, including rust stripping, oxide conversion and application of protective compositions based on oils or waxes.
For hidden cavities of the thresholds, special spray nozzles are used, which allow you to cover the internal walls with a protective layer. Popular compositions such as Movieville or more modern analogues on a paraffin basis, create an elastic film that does not crack in the cold and has the property of self-tightening with minor damage.
⚠️ Note: Do not use bitumen mastics to treat hidden cavities of sills. Bitumen eventually dries, cracks and begins to accumulate moisture under itself, turning into an ideal incubator for accelerated corrosion of the metal.
The outer parts of the sills are often protected with anti-gravel coatings. These are durable polymer compositions that are applied to purified and defatted metal. They create a rough layer, resistant to the impact of small stones. However, they should be applied carefully so as not to hide possible defects in the metal that need to be controlled in the future.
The galvanizing myth
Many people believe that the galvanized body does not rust. That's a misconception. Zinc protects steel only until it is broken. When deep scratching or chipping, the zinc layer is destroyed, and electrochemical corrosion begins, which can spread under the paint.
Design features of different types of bodies
The location and construction of the thresholds may vary significantly depending on the type of body. In sedans and hatchbacks, the rapids are usually part of the load-bearing body and are closed with decorative overlays. Owners of these cars It is necessary to remember the hidden drainage holes.which can clog the foliage, causing the accumulation of water inside.
The situation with frame SUVs is different. There, the rapids are often an extension of the frame or attached to it, and their main function is to protect against dirt and ease of landing. They can be removable and made from a tubular profile. Replacing or repairing such elements is easier, but damage to them when driving off-road occurs much more often due to low clearance.
- 🚗 Sedans: Thresholds integrated into the body, complex geometry, high risk of hidden corrosion in the joints.
- 🚙 SUVs: often have reinforced or removable tube sills, the main threat is mechanical damage from stones.
- 🚐 Minivans: Low landing requires strong rapid protection, often equipped with a wide footboard along the entire length.
Understanding these differences helps to plan the service correctly. For the city sedan, chemical protection from reagents is more important, while for the SUV, mechanical strength and protection from shocks are the priority. Regular inspection of the lower part of the car will allow you to notice changes in time and prolong the life of the car.
Regular washing of sills from the inside (through drainage holes) and treatment with anticores every 2-3 years increase the service life of the body by an average of 5-7 years.
Frequently Asked Questions (FAQ)
Can I drive with rotten rapids?
You can drive, but it's not safe. Thresholds are an element of the power structure of the body. In a side impact, they take the main load. If the metal rotted, the body can fold like a house of cards, which is deadly for passengers. In addition, through the holes in the cabin will get water and exhaust gases.
How much does it cost to replace the thresholds?
The cost depends on the brand of the car and the region. The work to replace one threshold can cost from 10 000 to 30 000 rubles and above, not counting the cost of metal and painting. Complete digestion of the rapids is often equated with serious body repairs.
How often should I do anticor thresholds?
Modern quality compositions serve from 3 to 5 years. However, in conditions of aggressive winter operation with a large amount of salt, it is recommended to carry out treatment every 2 years, making a preventive inspection once a year.
Is it true that plastic doorsteps cause rust?
Yes, this is true if moisture and dirt get under them, and there is no air access. Plastic creates a sealed environment where metal is shed. It is recommended to periodically remove the linings, clean the space under them and treat the metal with protective compositions.