Restoring the integrity of the sills is not just a matter of aesthetics of the car's appearance, but also a critical procedure for maintaining geometric rigidity body It is these elements that bear the main load during side impacts and prevent deformation of the roof and floor. Ignoring the first signs of corrosion or mechanical damage can lead to repairs becoming economically unfeasible.
A repair kit for thresholds is a ready-made set of elements designed to replace rotten or deformed areas without the need for complex adjustments. Unlike universal metal sheets, such kits are often designed for specific models or groups of cars, which greatly simplifies the work. The use of specialized parts allows you to restore factory strength parameters.
Choosing the right kit requires understanding the differences between materials and construction types. On the modern auto parts market you can find both budget options made of thin metal and professional solutions with a reinforced structure. The durability of the repair and the resistance of the body to the reappearance of rust directly depend on the quality of the selected repair kit.
Design features and types of repair kits
The main classification of repair kits is based on the material of manufacture and the method of integration into the body. The traditional solution remains stamped steel inserts, which completely repeat the geometry of the factory thresholds. They require welding, but provide maximum rigidity and reliability of the connection, completely restoring the load-bearing frame.
The second popular option is overhead thresholds made of plastic or composite materials with a metal base. Such elements are often used to protect entire metal or mask small defects, but they cannot be considered a full-fledged repair solution for serious corrosion. They are not suitable for restoring the power structure.
⚠️ Attention: Using overhead plastic thresholds over rotten metal will only hide the problem, but will accelerate the destruction of the body due to the accumulation of moisture between the plastic and metal.
There are also hybrid solutions, where the outer part is made of durable polymer, and the internal power part is made of steel. When choosing, it is important to pay attention to the thickness of the metal: a high-quality part should not be thinner than 0.8–1.0 mm. Thin metal will quickly burn through welding or rust in no time.
Why is metal thickness important?
Thin metal (less than 0.7 mm) is prone to warping and burning during welding. This requires a highly qualified welder and the use of argon welding, which increases the cost of repairs.
Criteria for choosing a quality set
When purchasing a repair kit, the first thing you need to do is evaluate the quality of the packaging and the presence of a protective coating. Good parts are supplied in individual packaging with a layer applied soil or zinc coating. Lack of protection means that the part will begin to tear before installation if it is not treated independently.
The second critical parameter is the accuracy of the geometry. Cheap Chinese analogues often suffer from mismatched mounting holes or curved profiles. Before purchasing, it is recommended to check the part number with the manufacturer’s catalog for your specific modification car.
It is also worth paying attention to the set's contents. In addition to the thresholds themselves, a high-quality repair kit may contain:
- 🔩 Specialized fasteners and clips.
- 🛡️ Sealing elastic bands to prevent moisture from entering.
- 🧪 Sample of anti-corrosion composition for treating seams.
- 📐 Installation instructions indicating welding points.
Don't skimp on your purchase by choosing the cheapest option on the market. Cheapness is often due to the use of recycled metal or violation of stamping technology, which will lead to difficulties during installation.
Necessary tools and preparation
For professional installation of a repair kit, you will need not only a set of tools, but also a properly equipped workplace. The main tool is semi-automatic welding machine (MIG/MAG), allowing spot and seam welding without overheating the metal. Gas welding is not recommended in this case due to the risk of deformation of thin-walled elements.
In addition to welding, you will need:
- 🔪 Angle grinder (grinder) with cutting and cleaning wheels.
- 🔨 Straightening hammers and anvils for straightening seats.
- 🌡️ Industrial hair dryer for working with sealants and anticorrosive materials.
- 🧹 Degreaser and rags for preparing surfaces.
☑️ Preparation for welding
Pay special attention to body preparation. All rusty areas must be cut out to bare metal. The boundary between the old and new metal should be smooth, without torn edges, which will ensure a high-quality fit of the weld.
Replacement technology and welding work
The installation process begins with dismantling the old thresholds. If they are held on by spot welding, it is necessary to drill out or cut off the mounting points, being careful not to damage the body pillars. After removing the old threshold, the internal amplifiers are inspected and, if necessary, replaced.
Installation of a new element is carried out in several stages. First, the part is fixed with clamps and tack welding is done in several places. Then the body geometry and door opening are checked. Only after successful fitting is a continuous fusible weld with the step recommended by the manufacturer.
Welding mode: Current 60-80A, Wire 0.8 mm, Gas Ar/CO2It is important not to overheat the metal by pausing between welding passes. Overheated metal loses its strength properties and is more susceptible to corrosion in the future. The seams must be continuous, without pores or cavities.
Use the copper plate as a heat sink when welding thin sections to prevent burn-through and warping of the part.
Anti-corrosion protection and finishing
After completing the welding work and cleaning the seams, the most important stage begins - anti-corrosion treatment. The weld is a vulnerable spot, so it must be coated with epoxy primer. Ordinary acidic primer cannot be used in this case, as it can cause corrosion.
The internal cavities of the thresholds must be blown and treated paraffin-containing compounds or special anticorrosive agents with a long spray nozzle. This creates a protective film from the inside, preventing rust from developing in hidden cavities.
| Coverage type | Purpose | Service life | Application Features |
|---|---|---|---|
| Epoxy primer | Primary seam protection | 5-7 years | Requires perfect surface preparation |
| Movil | Protection of internal cavities | 2-3 years | Penetrates microcracks and takes a long time to dry |
| Liquid plastic | Stone impact protection | 3-5 years | Creates a thick elastic layer |
| Zinc-containing soil | Cathodic protection | 10+ years | Best protection against galvanic corrosion |
The final coating is selected depending on whether the threshold will be painted in body color or remain black. Black thresholds often use textured paint or abrasion-resistant polyurethane coating.
⚠️ Attention: Never apply anticorrosion agent to areas intended for future welding or mounting holes. This will lead to paint peeling and contact failure.
Common repair mistakes
One of the most common mistakes is neglecting to clean the metal before welding. Residues of paint, rust or oil cause the weld to become weak and quickly deteriorate. The metal must be cleaned to a characteristic metallic shine.
Another mistake is the wrong choice of welding current. Too much current burns through the metal, and too little does not provide penetration. It is necessary to select the mode on test samples of the same thickness as the part being repaired.
The quality of surface preparation determines 80% of the success of anti-corrosion protection. Not even the most expensive anti-corrosion agent will resist rust or oil.
Also, craftsmen often forget about drainage holes. There should be holes at the bottom of the thresholds for condensate drainage. If they are welded or clogged with sealant, water will constantly accumulate inside the threshold, which will lead to rapid rotting from the inside.
Cost of work and feasibility of repairs
The price of a repair kit varies depending on the make of the car and the manufacturer of the part. For mass models of domestic and Chinese production, the cost of the kit can range from 2 to 5 thousand rubles. For premium foreign cars, the price can reach 15–20 thousand rubles per side.
The cost of replacement work in a specialized service usually exceeds the cost of the part itself by 2-3 times. This is due to the labor-intensive process: dismantling the interior, welding, putty, painting and anti-corrosion. However, independent repairs without experience can lead to damage to the body.
The feasibility of repairs depends on the general condition of the car. If the body has rotted by more than 40–50%, replacing the thresholds may not be economically justified. In such cases, it is easier to consider buying another car or completely re-welding the body, which is an extremely expensive procedure.
Impact on the cost of the car
Qualitatively replaced thresholds with documents can increase the liquidity of the car, but not its market value. Buyers will still consider the car "damaged" or "restored."
Frequently asked questions (FAQ)
Is it possible to replace thresholds without welding, using only sealant and rivets?
Theoretically, this is possible for decorative purposes or on old cars that do not require preservation of the power structure. However, for a modern car this method is unacceptable, since the thresholds are a power element of safety. A riveted joint will not withstand the impact of an accident and will quickly collapse from vibration.
How often does the anti-corrosion coating of thresholds need to be renewed?
The recommended frequency of inspection and renewal of anticorrosive coating is once every 2–3 years. When operating a vehicle in harsh climates, using reagents on roads or frequently washing under pressure, the interval should be reduced to 1 year.
What is the difference between the original repair kit and the analogue one?
Original parts (OEM) are made of metal of the same grade and thickness as the car body, and have ideal geometry. Analogues may be made of softer steel, have a smaller thickness and require additional adjustment (“trying on”) before installation.
Do I need to remove the doors when replacing thresholds?
In most cases, it is not necessary to remove the doors, but they will have to be removed from the hinges or moved to the side as much as possible, secured in order to provide access to the upper welding points and not damage the paintwork from sparks.
What is the service life of a correctly installed repair kit?
If welding technology and high-quality anti-corrosion treatment are followed, the service life of the repair kit ranges from 7 to 10 years or more. The key factor here is not so much the part itself, but the quality of protection of welds and internal cavities.