Replacing a car threshold with your own hands: a detailed guide with photos and videos

Car sills are one of the most vulnerable parts of the body, which is the first to take impacts from road salt, gravel and mechanical damage. Over time, even neat cars develop holes, rust, or deformations after an accident. Replacing a threshold at a car service costs 15,000–40,000 rubles (depending on the model and complexity of the work), but if you have the tools and patience, you can perform this operation yourself.

In this article we will analyze the entire process from A to Z: how to choose repair threshold or original part, what tools are needed, how to properly cut off the old part and weld a new one, and also how to protect the metal from corrosion for many years. We will pay special attention to the typical mistakes of beginners that lead to rapid re-rotting of the threshold due to improper treatment of seams or lack of anti-corrosion protection. If you have never held a welding machine in your hands, it doesn’t matter: we will give alternative methods of fastening (with bolts or rivets) and tell you when you can get by with them.

When a threshold replacement is required: signs and diagnosis

Not every threshold defect requires a complete replacement - sometimes local repairs or anti-corrosion treatment are sufficient. However there is critical signs, in which it is impossible to delay replacement:

• 🔴 Through holes - even small holes (1–2 cm in diameter) quickly grow due to moisture and dirt getting inside the threshold.
• 🔴 "Saffron milk caps" under the paintwork - swelling of the paint signals internal corrosion, which is already destroying the metal.
• 🔴 Deformation after an accident — if the threshold is bent in such a way that it interferes with the opening of the doors or violates the geometry of the body.
• 🔴 Amplifiers rotting - if a dull sound is heard when tapping the threshold (a sign of destruction of internal elements).

For an accurate diagnosis, take flat blade screwdriver and gently tap the threshold along its entire length. Healthy metal makes a ringing sound, while rusty metal makes a dull sound. Also inspect the places where the threshold is attached to the side members and pillars: if there are traces of rust there, there is a high probability that corrosion has already “eaten” the load-bearing elements.

⚠️ Attention: If the threshold is rotten at the place where the seat belt is attached (usually the center pillar), drive the car prohibited - This is a threat to the lives of passengers in an accident. In such cases, urgent replacement is required to restore the load-bearing capacity of the body.

Before starting work, be sure to check the condition neighboring elements: lower part of the door, wheel arch and side member. Corrosion often spreads further than it seems at first glance. If you ignore these areas, the new threshold will not last more than a year.

Choice of spare parts: original vs. analogue vs. repair threshold

The correct choice of part depends on 50% success repair. There are three types of thresholds on the market:

Threshold type	Pros	Cons	Cost (RUB)
Original (OEM)	Perfect fit, factory quality metal, full compatibility with the body	Expensive, long wait (on order), often sold only complete with amplifiers	8 000–25 000
Analog (non-original)	Cheaper than the original, wide range, often includes amplifiers	May require modification (adjustment), metal quality is worse	3 000–12 000
Repair (partial)	Low price, suitable for local repairs, does not require complete dismantling	Only for small areas, difficult to fit, often thin metal	800–3 500

For most cars the best choice is analogue from trusted manufacturerssuch as Febi, Meyle or SASIC. When purchasing, be sure to check:

• 📋 Is it included in the package threshold amplifier (if not, you will have to buy it separately or use the old one).
• 📋 Is there technological holes for fastening the casing and wiring (cheap analogues may not have them).
• 📋 Does the thickness of the metal correspond to the original (repair thresholds often have 0.6–0.8 mm instead of 1.0–1.2 mm).

If you are renovating foreign car over 10 years old, pay attention to the thresholds from disassembly - they are cheaper than new ones and have already been “run-in” with time. The main thing is to carefully inspect them for hidden corrosion (especially inside the amplifier).

Tools and materials: complete checklist

To replace the threshold you will need specialized tool, but most of it can be rented or rented. Here is the minimum set:

Angle grinder (grinder) with cutting and grinding wheel|Welding machine (semi-automatic MIG/MAG or inverter) + chameleon mask|Set of drills and step cutter for drilling points|Riveter and set of aluminum/steel rivets|Hammer, chisel, set of screwdrivers and keys|Anti-corrosion compounds (ML-mastic, zinc spray, primer)|Putty, sandpaper (P80–P240), degreaser|Jack, body stands, door ties-->

If you plan to cook the threshold in a garage without an inspection hole, prepare:

• 🔧 Lift or jack with supports - the body must be securely fixed at a height 50–70 cm from the floor.
• 🔧 Fire screen — welding sparks can burn through the floor or wallpaper (if you work in a box).
• 🔧 Hood or fan — fumes from welding and priming are toxic.

For anti-corrosion treatment we recommend using:

• 🛡️ ML-mastic (for example, Dinitrol ML) - for internal cavities.
• 🛡️ Zinc spray (for example, Zinc Rich Primer) - for external protection of welds.
• 🛡️ Primer-sealant (for example, 3M Body Schutz 859) - for final processing before painting.

⚠️ Attention: Do not use for cutting threshold gas welding — it overheats the metal and disrupts its structure. Bulgarian woman with cutting wheel 1.0–1.6 mm gives an even cut without thermal deformation.

What is the difference between MIG and MAG welding?

MIG (Metal Inert Gas) uses inert gas (argon or helium) and is suitable for welding non-ferrous metals. MAG (Metal Active Gas) works with active gas (carbon dioxide or its mixture with argon) and is optimal for steel - this is the method needed for body work. For thresholds, a semi-automatic device with amperage is sufficient 80–120 A and wire diameter 0.6–0.8 mm.

Step-by-step instructions: how to replace the threshold with your own hands

The whole process can be divided into 5 Key Stages. Let's look at each in detail.

1. Dismantling the old threshold

Start by preparing your car:

1. Remove doors (or at least disconnect them so they don’t interfere). To do this, unscrew the hinges and remove the wiring (don't forget to label the connectors!).
2. Remove interior trim and plastic sill plates - additional fastenings are often hidden under them.
3. Disconnect wiring (for example, door sensors or lights).

Next, start cutting:

• 🔪 Map cutting line marker - it should go along the factory welds (usually the junction of the threshold with the spar and racks).
• 🔪 Drill out rivets (if any) with a step cutter.
• 🔪 Carefully cut the threshold with a grinder, leaving 1–2 cm metal for future welding of a new one.

After removing the threshold, clean thoroughly welding residue and finish the edges rust converter (for example, Tsinkarem). If there are traces of corrosion on the spar or rack, they also need to be cut out and welded patches.

2. Fitting a new threshold

Before welding, a new threshold is needed try on and adjust:

• 📏 Attach the part to the installation site and check the gaps - they should not exceed 1–2 mm.
• 📏 If necessary, trim the threshold with a grinder or metal scissors.
• 📏 Drill technological holes for fastening the casing (if they are not included in the kit).

Please note threshold amplifier - it should fit snugly to the body. If you are using an old amplifier, clean it of rust and welding residue. In some cases, the amplifier has to cook separately, and only then attach the outer threshold.

3. Welding the threshold

This is the most critical stage. Follow the algorithm:

1. Secure the threshold clamps or self-tapping screws at several points so that it does not move during welding.
2. Start cooking with joints with spar and struts - strong long seams are needed here 20–30 mm in increments 3–5 cm.
3. Then boil lower part of the threshold (if it is two-level).
4. Brew at the end technological holes and finish the seams sander.

For welding, use the following modes:

• 🔥 Current strength: 90–110 A (for metal thickness 0.8–1.2 mm).
• 🔥 Wire feed speed: 4–6 m/min.
• 🔥 Gas: carbon dioxide (CO₂) or Ar/CO₂ mixture (80/20).

⚠️ Attention: Don't boil the threshold continuous seam - this will lead to deformation of the metal due to overheating. It is optimal to alternate welding sections and allow the metal to cool (you can pour water through 1–2 minutes after welding).

4. Anti-corrosion treatment

After welding, the threshold is needed protect against rust:

1. Clean the seams metal brush and degrease acetone.
2. Apply zinc spray on all welds and internal cavities.
3. Process threshold ML-mastic (using a spray gun or brush).
4. Apply sealant primer on the external surface before painting.

For internal cavities use mastic with wax (for example, Tectyl ML) - it does not harden completely and protects the metal even in case of mechanical damage. Don't forget about drainage holes (if they are in the threshold design) - they need to be cleaned and processed separately.

5. Painting and assembly

Final stage:

• 🎨 Fill up any uneven surfaces and sand the surface (sandpaper P240–P400).
• 🎨Apply acrylic primer in 2–3 layers.
• 🎨 Paint the threshold in the body color (use auto enamel with hardener).
• 🎨 After drying, install the trim and doors, connect the wiring.

If you paint the threshold spray can, keep him at a distance 20–30 cm and apply thin layers at intervals 10–15 minutes. For best results use intermediate drying infrared lamp.

Alternative methods of fastening the threshold (without welding)

If you do not have a welding machine, the threshold can be secured:

• 🔩 On rivets — Suitable for repair thresholds or temporary fastening. Use aluminum rivets with a diameter 4–5 mm in increments 3–4 cm.
• 🔩 Bolted - more reliable than rivets, but requires drilling holes in the body. The bolts must be M6–M8 with growers.
• 🔩 On glue - only for small patches! Use two-component adhesive (for example, 3M 08115) together with rivets.

Disadvantages of the non-welding method:

• ❌ Less strength (especially during side impacts).
• ❌ Risk of corrosion at fastening points (if the seams are not sealed).
• ❌ It is difficult to ensure tightness (you need to use seam sealant, for example, SikaFlex).

If you choose rivet fastening, follow the algorithm:

1. Drill holes in the threshold and body (diameter 0.1 mm more rivets).
2. Finish the edges anticorrosive and apply sealant at the joints.
3. Install the rivets riveter, starting from the edges and moving towards the center.
4. After installation, cover the seams zinc spray and mastic.

⚠️ Attention: No welding cannot be repaired thresholds on cars, where they are power part of the body (for example, on Volvo, BMW or Mercedes with supporting structure). In such cases, only welding guarantees safety.

Common mistakes and how to avoid them

Even experienced craftsmen sometimes make mistakes that shorten the service life of the threshold. Here are the most common:

Error	Consequences	How to avoid
Incomplete removal of rust before welding	Corrosion will continue to spread under a new threshold	Use sandblasting or rust converter, cut off all affected areas
Continuous seam welding	Metal deformation, cracks, overheating	Cook with short seams (2–3 cm) with breaks for cooling
Lack of anti-corrosion treatment inside the threshold	Rust from the inside destroys metal in 1–2 years	Treat internal cavities ML-mastic through technological holes
Using metal that is too thin (repair thresholds 0.6 mm)	The threshold bends under load and quickly rusts	Choose thresholds with a thickness of at least 0.8 mm (for SUVs - 1.0–1.2 mm)
Incorrect fit to body geometry	Door distortions, interior seal failure	Check the gaps along the entire length of the threshold, use screeds for fixing

Another common problem is incorrect painting. If you do not apply primer or paint on raw metal, bubbles and chips will appear within six months. Always follow the technology:

1. Degreasing → primer → drying → paint → varnish (if necessary).

And don't forget about drainage holes! They are often filled with mastic “for reliability”, but this leads to the accumulation of moisture inside the threshold. Clean holes once a year and process them anti-gravel.

Cost of replacing a threshold: comparison of self-repair and car service

The cost of replacing the threshold depends on car make, part type and region. Here are the approximate prices:

Service/Material	On your own (RUB)	Car service (RUB)
Threshold (analog)	3 000–12 000	5,000–20,000 (with extra charge)
Welding work	0 (if you have your own device)	8 000–20 000
Anti-corrosion treatment	1,500–3,000 (mastic, sprays)	3 000–6 000
Painting	2,000–5,000 (cans)	5,000–15,000 (camera)
TOTAL	6 500–20 000	21 000–61 000

The savings when doing your own repairs are obvious, but keep in mind hidden costs:

• 💰 Tool rental (welding machine, grinder) — 1,500–3,000 rub./day.
• 💰 Purchase of consumables (gas, wire, grinder circles) - 2,000–4,000 rub.
• 💰 Possible errors (for example, a damaged threshold due to unsuccessful welding).

If you have no experience, consider hybrid option: buy the threshold and anticorrosive yourself, and order welding and painting from a service center. This will save up to 30–40% budget.

FAQ: Frequently asked questions about replacing thresholds

Is it possible to replace the threshold without removing the doors?

Technically yes, but it is extremely inconvenient. Doors will interfere with fitting and welding and risk damage from sparks. If it is not possible to remove the doors, at least disconnect them (by unscrewing the hinges) and move them to the side, securing them with ropes.

Which welding machine is better to choose for thresholds?

Optimal semi-automatic MIG/MAG with current strength up to 160 A. Models suitable for home use:

• Svarog MIG 165 (budget option, ~25,000 rub.).
• BlueWeld Prestige MIG-200 (semi-professional, ~40,000 rub.).
• ESAB Rebel EMP 205ic (premium, ~100,000 rub.).

An inverter is sufficient for welding thresholds (for example, Resanta SAI-190), but it is more difficult for them to work - they require experience.

How long does it take to replace a threshold?

If you have experience and tools:

• 🕒 Dismantling the old threshold - 2–3 hours.
• 🕒 Fitting and welding of the new one - 3–5 hours.
• 🕒 Anticorrosive and painting — 4–6 hours (including drying).

Total: 1–2 days (with breaks for the metal to cool). Beginners may need up to 3–4 days.

What should I do if, after replacing the threshold, the doors do not close well?

This means that it is broken body geometry. Possible causes and solutions:

• 🔧 Threshold set not up to par → digest using laser level or template.
• 🔧Deformed door hinges → adjust or replace.
• 🔧 The fastening is broken racks → check the welds at the junction of the threshold and the pillar.

If the problem persists, contact slipway (stand for body straightening).

How often do you need to update the anticorrosive on thresholds?

Service life of anti-corrosion treatment:

• 📅 ML-mastic - once every 2–3 years.
• 📅 Zinc spray - once every 1–2 years (especially in places where there are chips).
• 📅 Seam sealant — check once a year, update if damaged.

After winter, be sure to wash the thresholds under pressure (for example, at a car wash) and process anti-gravel.