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Rear Sill & Wheel-Arch Repairs

It’s hard to believe it, but some of the older Mk1 MX-5s are now well over 30 years old! Over the last few years we have seen a steady increase in the number of badly corroded MX-5s, particularly older UK specification models which have been subjected to years of British winters and salty roads, but even the Japanese import models and newer Mk2’s and Mk2.5's are also now suffering, especially if they have been in the UK for a while. The normal corrosion area is limited to the rear outer sill section and rear wheel arches. This is often due to the hood rain channel drain tubes becoming blocked, which in turn causes the collecting tray to overflow and allow water to run down into the sills instead of exiting through the drain tubes. If the small sill drain holes are also blocked (which they usually are) then the water will sit inside the sills and gradually corrode the sill from the inside outwards. The first visible indication is usually when the outer sill and wheel arch starts to bubble up, by which time, of course, it is too late. The damage has been done. Up until recently, this sort of corrosion problem has usually meant the end of the road for the car, as a proper repair was deemed uneconomical. The good news is that there is now a strong demand for older MX-5s in good condition as they have truly gained “Classic Car” status. This coupled with the recent introduction of quality sill and rear wheel-arch repair panels for both the Mk1 and Mk2/2.5 MX-5 means that a proper and cost effective repair is now a viable solution. There’s no longer any need to scrap your cherished MX-5. Mazda’s legendary mechanics means that even 25 year old MX-5s are still reliable cars, so provided the bodywork is properly repaired and maintained, your car should continue to give many more years’ good service. In fact, as time goes on, the car’s depreciation cost should become virtually zero. Of course this will only be true if the corrosion is addressed correctly. All too often we see poor quality repairs being carried out, with “patched-up” welded plates hastily applied to sills to get the car through the MOT test. This sort of repair can only be regarded as short term and will end up costing more in the end by not lasting very long and devaluing the car significantly. Our permanent solution involves carefully cutting out and removing all the corroded metal from the sill and wheel arch, using a miniature CCTV camera (endoscope) to probe the internal structure and investigate the full extent of any rust. We then etch-prime and seal the internal panels before welding in new outer sill and wheel arch pieces. The panels are precisely fitted using a butt-welding technique that avoids creating any overlapped joints, which often leads to trapped moisture and can cause future corrosion problems.

Once welded and sealed, the panel is then re-painted in our low-bake paint booth to the original specification. The final process involves carefully injecting and applying “Waxoyl” anti-corrosion protection treatment to the repaired areas. The full process takes approximately one week to complete and costs between £ 1,000 to £ 1,800 per side (inclusive of all parts, materials, paintwork and corrosion protection and VAT), depending upon the severity of the corrosion.

Click here for further information and photographs of Mk1 NA restoration or Click here for information and photographs of Mk2/2.5 NB models.

The pictures below show repairs to a Mk2.5 model, but the work is essentially the same for the earlier models.

As well as carrying out sill and wheel-arch repairs, we are, of course, fully equipped to carry out any aspect of restoration work on your MX-5. Please give us a call or drop us an email to discuss your requirements.

Telephone: 01977 233 555  or Email:

Stock Availability: Call us to book now
  • Part Number: RSWR123
  • Stock Availability: Call us to book now