Replacing or restoring thresholds is one of the most critical operations to maintain a car body in good condition. It is these structural elements that take the brunt of road reagents, moisture and mechanical damage, turning over time into centers of corrosion. If you notice blistering paint or through holes, then the question of how to make thresholds on a car becomes a priority for the owner.
Timely intervention allows you not only to return the car to a neat appearance, but also to significantly extend the service life of the supporting structure of the body. Ignoring the problem can lead to corrosion will spread to the side members and the interior floor, which will require major and expensive repairs. In this article we will analyze in detail all the stages of work, the necessary tools and technologies that will allow the replacement to be carried out efficiently.
The restoration process requires the master to have certain skills in working with metal and welding equipment. However, if you have a theoretical basis and are careful, you can make thresholds in your own garage. It is important to understand that tightness connections and high-quality anti-corrosion treatment are the key to long-lasting results.
Diagnosis of condition and selection of materials
Before starting any work, it is necessary to conduct a thorough diagnosis of the current condition of the thresholds. Often external signs of destruction are just the “tip of the iceberg”, and the actual area of metal damage turns out to be much larger. To evaluate, tapping with a hammer is used: a dull sound indicates peeling metal or hidden rust.
The choice of replacement material directly affects the durability and complexity of installation. On sale you can find ready-made stamped thresholds that perfectly match the geometry of the body, or universal profile pipes that require adjustment. Stamped elements preferable for beginners, as they minimize the risk of errors during assembly.
- 🚗 Stamped thresholds: a ready-made solution that requires minimal adjustment, but is more expensive to purchase.
- 🔩 Profile pipe: cheaper and more versatile, allows you to create reinforced structures, but requires a highly qualified welder.
- 🛡️ Repair inserts: fragments for partial replacement, suitable for local damage without dismantling the entire threshold.
Particular attention should be paid to the thickness of the metal. Material that is too thin will quickly burn out during welding or begin to rot after a year or two of use. The optimal thickness is considered to be 0.8–1.2 mm. It is also important to choose the right anti-corrosion composition for treating internal cavities before installation.
⚠️ Attention: If corrosion has affected more than 30% of the threshold area and has affected the fastening of doors or pillars, partial repairs do not make sense - a complete replacement of the element is necessary.
Do not skimp on consumables such as welding wire or electrodes. The use of low-quality components can lead to the formation of pores in the seams and reduced joint strength. Before purchasing, make sure the materials you select are compatible with the type of metal on your vehicle.
Necessary tools and workplace preparation
High-quality body work is impossible without proper equipment. A basic set of tools should include not only a welding machine, but also tools for cutting, stripping and fixing metal. Best suited for garage work semi-automatic welding machine (MIG/MAG), operating in a protective gas environment.
Preparing the work area is a step that is often ignored, resulting in injury or vehicle damage. Ensure good lighting and ventilation, as welding operations produce harmful gases and bright radiation. It is also necessary to remove all flammable materials from the work area.
List of required equipment for replacing thresholds:
- 🔥 Welding machine: semi-automatic with a cylinder of a mixture of argon and CO2 or carbon dioxide.
- 🪚 Angle grinder (grinder): with a set of cutting and cleaning wheels for metal.
- 🔨 Body tools: hammers, mallets, clamps, alligator clips for fixing parts.
- 🧤 Protective equipment: chameleon mask, leggings, respirator and protective suit.
It is worth mentioning separately clamps and clips. They are critical for accurately positioning the new threshold relative to the doorway. The slightest misalignment will lead to problems with opening doors or loose seals. Check in advance the serviceability of all power tools and the availability of consumables.
Removing the old threshold and cleaning
The process of removing the old threshold begins with the dismantling of all hanging elements: moldings, plastic trims, and sometimes doors if they interfere with access. The doors do not need to be completely removed, but they must be securely fixed in the open position or removed from the hinges so as not to be damaged when working with an angle grinder.
Use for cutting metal cutting wheels minimum thickness to minimize heating and deformation of adjacent areas of the body. The cut should be made indented from the whole metal, leaving a margin for subsequent stripping. It is important not to damage the internal reinforcements and body pillars if they are in good condition.
Cutting sequence:1. Cut off the outer part of the threshold along the top seam.
2. Make vertical cuts at the front and rear posts.
3. Carefully bend and cut off the inside.
After dismantling, it is necessary to thoroughly clean the welded joints to bare metal. Use cleaning wheel or a metal brush on an angle grinder. All remaining old paint, rust and sealant must be removed. New welds can only be applied to clean metal.
⚠️ Attention: When working with an angle grinder, be sure to use safety glasses and gloves. Flying metal shavings can cause serious injury to the eyes and skin.
If, after removing the threshold, hidden damage to the side members or floor is discovered, they must be eliminated before installing the new part. Ignoring these defects will lead to the fact that the new threshold will rest on a “rotten” foundation and will not last long. If necessary, cut out damaged areas and apply repair patches.
Technology of welding and installation of a new element
Installation of a new threshold begins with fitting. The part should fit into place without gaps or distortions. Secure the threshold with clamps and check the gaps between the threshold and the door, as well as the correspondence of the body lines. Only after a perfect fit can you begin to tack.
Welding should be done with short seams (1-2 cm) in a checkerboard pattern. This avoids overheating of the metal and warping of the structure. Allow the metal to cool between passes, tapping the seam with a hammer to relieve thermal stress. Temperature is a key success factor.
☑️ Check before welding
Pay special attention to the junction of the threshold and the pillars. Here the seam must be as tight and durable as possible, since these units bear the main load when the body is twisted. If a profile pipe is used, it must be welded around the entire perimeter, ensuring complete penetration.
| Parameter | Recommended value | Note |
|---|---|---|
| Welding current | 80–120 A | Depends on the thickness of the metal |
| Wire diameter | 0.8–1.0 mm | Optimal for bodywork |
| Feed rate | Average | Adjustable by experience |
| Shielding gas | CO2 or mixture | Prevents oxidation |
After completing the welding work, the seams must be cleaned with a grinder with a flap wheel. The surface should become smooth, without sharp transitions or sagging. This will prepare the base for applying putty and ensure an even paint job. Avoid leaving sharp edges that could injure your hands or cause corrosion.
Anti-corrosion treatment and sealing
The most common mistake newbies make is neglecting internal threshold processing. Even the best quality welding will not save the metal from rotting from the inside if moisture gets in. To protect internal cavities, special anticorrosive in aerosol cans with a long nozzle or guns for liquid formulations.
The application technology is simple: through technological holes (or specially drilled ones) the composition is sprayed inside the cavity. It is important to cover all hard-to-reach places, welds and hidden cavities with the composition. Movil or similar oil-based compounds create an elastic film that does not crack due to vibration.
The Secret to Durability
The most vulnerable places are the lower internal corners and welding areas. This is where you need to direct the anticorrosive jet first. Re-treatment is recommended every 2-3 years.
External seams and joints must be carefully sealed. For this purpose, automotive sealants are used, which remain elastic after drying. Apply the sealant in an even layer, forming a neat bead. This will prevent water from getting under the paint and into the interior of the car.
- 💧 Movil: penetrating lubricant, displaces moisture, suitable for hidden cavities.
- 🛢️ Bitumen mastics: create a thick protective layer, but do not penetrate microcracks.
- 🧪 Liquid plastic: forms a durable polymer film that is resistant to stone impacts.
⚠️ Attention: Never paint over the sealant immediately after application. Let it dry according to the manufacturer's instructions, otherwise bubbles will form under the paint.
Finishing and painting
The last stage is bringing the threshold into a marketable state. An epoxy primer is applied to the cleaned metal, which provides adhesion and additional protection against corrosion. After the soil has dried, the surface is puttied to level out small irregularities and transitions.
The putty should be applied in thin layers, allowing each layer to dry. After sanding, the surface should be perfectly smooth to the touch. Then the base paint and varnish are applied. If the color of the car is complex (metallic, mother-of-pearl), it may be necessary to paint the entire side to avoid different colors.
Use an adapter (solvent) when painting part of a part so that the border between new and old paint becomes invisible.
The quality of painting directly depends on the preparation of the surface and the conditions in the paint booth (or clean garage). Dust and drafts can ruin the whole job. After the varnish has dried, the surface can be polished to achieve a factory shine.
The main secret to success is not to rush to apply the next layer. The timing between primer, paint and varnish is more important than the speed of work.
Regular care of updated thresholds will extend their life. Washing your car, especially in winter, helps remove aggressive salts. Periodically check the condition of the protective coating and, if necessary, update the anti-corrosion treatment.
Frequently asked questions (FAQ)
Do I need to remove the doors to replace the threshold?
It is not necessary to remove the doors, but it is highly recommended. This will provide free access to welding areas, allow better control of gaps and protect the doors from sparks and tool damage. If the doors cannot be removed, they must be carefully covered with non-combustible material.
Which gas is better to use for welding: CO2 or a mixture?
For body work, a mixture of argon and carbon dioxide (for example, 80/20) is better suited. Pure CO2 produces a harder arc and more spatter, and also requires more power to achieve penetration. The mixture provides a more stable arc, less spatter and a better appearance of the seam, which is critical for thin body metal.
Is it possible to weld the threshold without removing the interior?
Theoretically it is possible, but it is very risky. Sparks from welding can burn through carpet, upholstery or wiring, and high temperatures can melt plastic parts of the interior. In addition, access to the inside of the threshold for cooking will be limited. It is recommended to vacate the interior as much as possible on the side of the threshold being replaced.
How long does it take for the anticorrosive agent to dry inside the threshold?
Drying time depends on the type of composition and ambient temperature. Oily compounds (such as Movil) can dry for several days, remaining liquid inside, which is even useful for self-healing scratches. Bitumen and polymer compounds dry faster, usually 24 hours at a temperature of +20°C. Complete polymerization can take up to a week.