Thresholds <em>Nissan Sunny FB15</em>: how to choose, replace and protect against corrosion

Nissan Sunny FB15 is one of the most popular models of the Japanese brand on the secondary market, but even with careful use, the thresholds of this car become a vulnerable point. Salt on the roads, mechanical damage and time take their toll: rust, dents and through holes appear after 5–7 years of service. In this article, we will look at how to diagnose problems with thresholds, which spare parts to choose for replacement, and whether they can be repaired without welding.

Feature FB15 — in the design of the sills, which are integrated with the side members and reinforced for improved body rigidity. This complicates repairs, but also makes them critically important: ignoring corrosion can lead to body deformation and geometry problems. We have collected proven solutions - from budget repairs to complete replacement with anti-corrosive agents, and will also tell you how to avoid common mistakes when working with thresholds of this generation Sunny.

Threshold design Nissan Sunny FB15: what you need to know before repair

Thresholds FB15 consist of three key elements: outer panel (visible part), internal amplifier (metal beam) and connecting points with side members. Unlike earlier models Sunny, here the amplifier is welded to the body at 8–10 points, which complicates dismantling. Important: if corrosion has affected the amplifier, simply replacing the outer panel will not solve the problem - complete dismantling and subsequent welding will be required.

Another feature - front and rear sills FB15 have different geometries due to the floor design. This means that the parts are not interchangeable: the left and right sides are also different. When ordering parts, be sure to specify VIN code or year of manufacture - in restyled versions (2014+), changes could be made to the fastenings.

• 🔧 External panel - thin metal (0.8–1 mm), most often rusts from the bottom and along the edges.
• 🛠️ Amplifier — thickness 1.2–1.5 mm, corrodes from the inside due to accumulating moisture.
• 🔗 Connecting points — critical for body rigidity; when cut with a grinder, they may weaken.

⚠️ Attention: If during inspection you find rust on the welds of the amplifier, this is a signal that the threshold needs to be completely replaced. Local repairs in this case will give a temporary effect (1-2 years), after which corrosion will return.

Diagnostics of threshold condition: when replacement is required

The first signs of problems with thresholds FB15 often go unnoticed. Start with a visual inspection:

1. Lift the car on a lift or drive it onto an overpass.
2. Clean the thresholds from dirt (use a wire brush or sandblast).
3. Check the integrity of the paintwork, especially at the joints with the arches.
4. Tap the thresholds with a wooden hammer - a dull sound indicates internal corrosion.

Critical symptoms requiring immediate attention:

• 🚨 Through holes - even small (5–10 mm) holes accelerate the destruction of the amplifier.
• 🔩 Peeling of welds - a sign that the amplifier has lost strength.
• 📏 Geometry Deformation — if the threshold “walks” when pressed, the body has already lost its rigidity.

For an accurate diagnosis, use thickness gauge (a device for measuring the residual thickness of metal). The norm for the outer panel is 0.8–1 mm, for the amplifier — 1.2–1.5 mm. If the indicators are lower by 30% or more, the part must be replaced.

⚠️ Attention: Don't rely on appearance alone! Corrosion often starts from the inside, especially in the seat mounting areas and under the driver's feet. If there is any suspicion, it is necessary to remove the interior trim.

Selection of spare parts: original vs. analogues for Nissan Sunny FB15

When replacing thresholds from owners FB15 there are three options: original parts from Nissan, non-original analogues (for example, from Febi or Mapco) and used spare parts from the showdown. Each option has pros and cons:

Part type	Pros	Cons	Average price (for 1 threshold)
Original (Nissan)	Perfect fit, guaranteed against corrosion (2-3 years), retains factory hardness	High price, long delivery times (if made to order)	12 000–18 000 ₽
Non-original (Febi, Mapco)	Price is 30–50% lower than the original, fast delivery	May require adjustment, thinner metal thickness (0.7–0.9 mm)	6 000–10 000 ₽
Used from disassembly	The most budget option, suitable for temporary repairs	Risk of hidden corrosion, limited choice of color and condition	3 000–7 000 ₽

When choosing analogues, pay attention to:

• 📌 Catalog number - for FB15 current articles 62600-4M000 (right) and 62601-4M000 (left).
• 🔍 Country of manufacture - Taiwanese and Korean analogues are often more accurate than Chinese ones.
• 🛡️ Presence of anti-corrosion coating - some brands (for example, Febi) parts are supplied with factory primer.

Threshold replacement technology: step-by-step instructions

Replacing thresholds FB15 - a labor-intensive process that requires welding equipment and body work skills. Let's consider the main stages:

1. Dismantling old thresholds
   • Remove the doors and interior trim.
   • Cut out the outer panel with a grinder, leaving 1–2 cm of metal for subsequent welding.
   • Remove the reinforcement by first drilling out the weld spots.
2. Preparing new parts
   • Try on new thresholds and adjust them to fit if necessary.
   • Treat internal cavities with anticorrosive agent (use ML-mastic or Dinitrol).
3. Welding and assembly
   • Weld the amplifier to the body at 8–10 points (use spot welding or semi-automatic).
   • Install the outer panel, welding the seams in 2-3 cm increments.
   • Finish the seams epoxy primer and paint it.

Make sure the car is on a level surface|Disconnect the battery|Remove the negative terminal|Have a fire extinguisher ready (welding is a fire hazard!)|Check that all fasteners are present-->

Key points:

• 🔥 Welding - use wire ER70S-6 (diameter 0.8 mm) and gas Ar/CO2 (80/20).
• 🎨 Painting - after priming, apply 2 layers of base and 2 layers of varnish, drying between layers.
• ⚖️ Geometry control — after replacement, check the door gaps (should be 3–5 mm).

What to do if after replacement the thresholds rust again?

If corrosion appears within a year, the reason may be:

1) Poor quality anti-corrosion treatment of internal cavities.

2) Using cheap primers or paints without zinc.

3) Violation of welding technology (unwelded seams).

Solution: dismantle the thresholds, clean to bare metal and repeat the treatment using zinc-containing soils (For example, Body 992).

Anti-corrosion treatment: how to protect thresholds for a long time

Even new thresholds FB15 require additional protection. Standard factory treatment lasts 3-5 years, after which the metal becomes vulnerable. Effective methods:

• 🛡️ ML-mastic — applied to internal surfaces through technological holes. Duration of protection: 5–7 years.
• 🧪 Zinc soils (For example, Zinc Rich Primer) - create electrochemical protection. Suitable for weld seams.
• 🔧 Liquid fender liners (For example, Noxudol) - protect the lower part of the thresholds from abrasive wear.

Application technology:

1. Clean the surface to bare metal (use sandblasting or metal brush).
2. Degrease White spirit or Antisilicon.
3. Apply 2 coats of primer at 15 minute intervals.
4. After drying, cover with mastic (layer thickness - 1–1.5 mm).

⚠️ Attention: Do not use for threshold treatment bitumen mastic — it cracks at low temperatures and does not protect against electrochemical corrosion. Optimal choice: mastics based on rubber or polymers (For example, Tectyl or Waxoyl).

Repair without welding: when possible

If corrosion has affected only the outer threshold panel, and the amplifier is intact, you can do without welding. For this use:

• 🔧 Fiberglass patches — suitable for small through holes (up to 3–5 cm).
• 🧲 Epoxy resins with reinforcement (For example, 3M 05907) - restore strength by 70–80%.
• 🔨 Straightening followed by putty - only for dents without damaging the metal.

Fiberglass repair technology:

1. Cut out the rusty area, leaving a margin of 1-2 cm.
2. Apply epoxy resin to the back of the patch.
3. Press the patch to the threshold and secure it clamps for 24 hours.
4. Once dry, sand and paint.

Limitations of the method:

• ❌ Not suitable for amplifier - external panel only.
• ❌ Repair service life is 2-3 years (then re-treatment is required).
• ❌ Does not restore the factory rigidity of the body.

Common mistakes when repairing thresholds and how to avoid them

Even experienced craftsmen make mistakes that shorten the service life of repaired thresholds. Let's look at typical mistakes:

• 🔥 Using gas welding - overheats the metal, which leads to deformation. Solution: only semi-automatic or spot welding.
• 🧹 Incomplete rust removal — if pockets of corrosion remain, they will continue to spread. Solution: sandblasting or rust converter (For example, Tsinkar).
• 🎨 Painting without primer - the paint will peel off after 1-2 years. Solution: 2 layers epoxy primer + 1 layer acrylic primer.
• 📏 Ignoring Geometry — if the thresholds are installed crookedly, the doors will not close well. Solution: Check clearances laser level.

Another common mistake is saving on anticorrosion agents. Many people apply protection only on the outside, forgetting about the internal cavities. As a result, moisture accumulates inside, and corrosion returns after 1–2 years. Use sprayer with extended nozzle (For example, Krown) for processing hidden areas.

⚠️ Attention: If, after replacing the thresholds, the car begins to “steer” to the side when driving, this is a sign of a violation of the body geometry. Need to check for wheel alignment stand and possibly re-straightening.

FAQ: Answers to frequently asked questions about thresholds Nissan Sunny FB15

Is it possible to drive with rusty sills if they are not through?

In the short term, yes, but it is dangerous. Rust weakens the metal, and in the event of an accident, the thresholds will not be able to absorb the impact. In addition, corrosion spreads to the side members, which leads to loss of body rigidity. At the first signs of rust (paint bubbles, red spots), begin repairs.

How much does it cost to replace thresholds at the service?

The cost depends on the region and service station level:

• Replacement of one threshold (with painting): 15 000–25 000 ₽.
• Complete replacement of both thresholds: 30 000–50 000 ₽.
• Anti-corrosion treatment: 3,000–7,000 ₽ (additional).

Saving on spare parts (for example, choosing non-original ones) can reduce costs by 30–40%.

Which anticorrosive agent is best for thresholds FB15?

Optimal options:

• For internal cavities: ML-mastic or Tectyl 506 (penetration ability).
• For external surfaces: Waxoyl or Noxudol 700 (resistant to chips).
• For welds: Zinc primer Body 992 + epoxy primer.

Avoid cheap bitumen mastics - they crack at temperatures below -20°C.

Is it possible to restore thresholds using putty?

Putty is a temporary solution, suitable only for small dents without damaging the metal. It is not suitable for through corrosion or rust because:

• Does not restore structural strength.
• Absorbs moisture, accelerating corrosion underneath the layer.
• Cracks due to vibrations (for example, when driving off-road).

For serious damage, use welding or fiberglass patches.

How often should thresholds be checked for corrosion?

Recommended inspection frequency:

• Once every 6 months - for cars older than 5 years.
• 1 time every 3 months — if the car is operated in aggressive conditions (salt on the roads, high humidity).
• Before and after winter — mandatory washing of thresholds with anti-corrosion treatment.

Use endoscope (flexible camera) for inspecting internal cavities without dismantling the casing.