Protecting a Classic: 1986 Supra Underside Restoration

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Mk3 Toyota Supra

The Mk3 Toyota Supra (A70), produced between 1986 and 1993, marked a major shift in Toyota’s approach to performance cars.

With:

• Independent rear suspension

• A more complex rear subframe design

• Extensive use of boxed steel sections

…the Mk3 is both rewarding to drive, but vulnerable underneath if corrosion is left unchecked.

Even low-mileage examples aren’t immune. Factory coatings were never designed to last 35+ years, especially in damp, salted UK conditions. Preservation work like this is increasingly important as clean examples such as this one become rarer.

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This project came to us as a rare example of an extremely well looked after Supra, with just two owners, an exceptionally low mileage and a solid, honest base.

While the exterior presented well, the underside told a slightly more familiar story. Decades of age, old coatings, and early corrosion were beginning to take hold in key areas. The owner’s goal wasn’t over-restoration or shortcuts. It was long-term preservation, done correctly and sympathetically to the car, with a clean, show-ready look.

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Initial Strip-Down & Deep Inspection

Before any blasting or coating work began, the underside was fully stripped back of components where required and thoroughly inspected.

Old underseal and factory coatings can hide:

• Early corrosion

• Failing seams

• Moisture trapped against bare steel

Stripping allows us to see the true condition of the metal, not just what’s visible on the surface.

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Glass-Bead Media Blasting The Underside

With the underside fully stripped and assessed, the next critical step was media blasting using fine glass-bead.

Older vehicles like the Mk3 Supra often carry multiple generations of underseal, factory coatings, and previous touch-ups. Over time, these layers become brittle, crack, and trap moisture against the steel, accelerating corrosion rather than preventing it.

Media blasting allows us to remove:

• Thick, failing underseal

• Aged factory coatings

• Surface rust forming around seams and spot welds

…while exposing the true condition of the metal underneath.

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Blasting isn’t about making things look clean. It’s about proper preparation.

Applying epoxy or stonechip over old underseal or contaminated metal locks problems in place. Moisture, corrosion, and failing coatings continue working underneath, unseen.

Only once the metal was clean, bare, and consistent across the underside did we move on to rust treatment and protective coatings.

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Rear Subframe Restoration

The rear subframe was removed and treated as a standalone component.

Years of road grime and aged coatings were stripped back using precise blasting, allowing us to:

• Clean the metal fully

• Remove corrosion without thinning the steel

• Prepare the surface correctly for coatings

Once clean, the subframe was protected using:

• Rust converter to stabilise any remaining oxidation

• Epoxy primer to seal the metal

• A durable topcoat for long-term protection

This approach ensures the subframe isn’t just visually restored — it’s protected from the inside out.

While the rear subframe was off the car, we also replaced the original rubber bushings with high-quality red polyurethane bushes. These offer far greater durability and resistance to oil, heat, and age, helping keep the rear end tight, aligned, and predictable.

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Fuel Tank Restoration

Fuel tanks are often overlooked, yet they’re exposed to constant moisture, salt spray, and debris.

On this Supra, the tank was:

• Removed and drained to allow proper access to hard-to-reach seams, mounting points, and corrosion-prone edges before blasting and refinishing.

• Carefully blasted to remove corrosion and old coatings

• Treated with rust converter

• Sealed with epoxy primer before finishing

The result is a tank that’s clean, protected, and visually consistent with the rest of the underside; without compromising originality.

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Full Underside Treatment - Step by Step

With the underside fully cleaned and prepped, we moved into the protection phase.

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Rust Conversion

Any remaining surface oxidation was chemically stabilised using a rust converter. This halts corrosion at a molecular level and provides a sound base for coatings.

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Epoxy Primer (Grey)

A high-build epoxy primer was applied across the underside. Epoxy is critical here because it:

• Chemically bonds to bare steel

• Seals the metal from moisture and oxygen

• Offers far superior corrosion resistance compared to standard primers

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Stonechip Protection

The underside was then finished with stonechip coatings for impact resistance:

• White stonechip across the main floor pan

• Black stonechip around the transmission tunnel

This not only protects against road debris but also replicates a factory-style finish.

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Final Colour Choice

At the customer’s request:

• Underside finished in white

• Front subframe area finished in black

• Rear subframe finished in silver

This balanced aesthetics with practicality, keeping high-visibility areas clean while maintaining durability.

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Projects like this Mk3 Supra highlight why proper underside restoration matters, even on low-mileage, well-kept cars.

It’s not just about making everything look new. It’s about understanding the materials, the environment, and the long-term goal, then choosing the right processes to match.

If you’re preserving a classic, performance car, or long-term keeper, the underside deserves the same attention as the bodywork.