13.1 Repair of Mazda Miata rear wheelarch and wheel house

Before we began the work on the rear wing repair on the Miata, we make you a new tool offer. This time you can buy an electrode shoe for invisible spot welding, Image 1. Simply connected to the spot welding electrode, see Image 2. Made in heat resistant special copper alloy, M 328. Price: 22 $ or 14.5 £ or 19 € including shipping.

Image 1 Shoe for invisible welding spots.
Image 2 The shoe connected to the electrode.

The most rust prone and vulnerable area next to the door is the rear wheel arch. The main reason for the rust is the construction itself plus the fact that most cars are neglected. The construction can be seen in the book in chapter 19.

In almost all cars the wheel arch is built up of two panels, the rear wing and the wheelhouse. These two panels are joined by spotwelding. The first sign that something is going on is that the area between the welding spots became swollen, Image 3. This is usually a process which is developed slowly over many years. In the next step small blisters begin to be evident along the edge of the wheel arch, image 4. First at the lower part of the wheelarch but gradually evident higher and higher up . If examined closer, under the blister is always a hole through the sheet. To a beginning microscopic in size but eventually followed by visible holes and finally disappearance of part of the wheel arch, Image 5.

Image 3 As the rust process goes on the area between the spots is forced apart and the edge of the wheelarch became swollen, step one. 1. Wing or wheelarch 2. Wheelhouse 3. Welding dot 4. Rust
Image 4 Small “blisters” around the wheelarch in the second step in the rust process. First affected is the lower areas but the rust gradually creeps upwards. 1. Blisters
Image 5 Final stage or stadium three with loss of part of the wheelarch. Picture from a scrap yard.

To make it easy, we are going to follow the repair of the rear wing on a rather common car, a Mazda Miata, using an aftermarket part. Later a more unusual but similar repair will be demonstrated.

In Image 6 the new wheel arch is temporarily fitted to the car to see if the shape and fitment are correct. This was satisfying which not always is the case. Note that the new panel covers a part of the B-post.

Image 6 The fit of the new panel is roughly controlled.

When the new part has been found correct the time has come to remove the old and rusty wheel arch. Carefully, see the book, and only an inch wide part close to the edge. In Image 7 the wheel arch is removed and left is the rusty wheel house.

Image 7 The outer edge of the wheel house is free to inspect.

A new repair part for the wheel house was shaped by shrinking and stretching in the Eckold Kraftformer, Image 8. For simplicity reasons in lengths of approximately 300-350 mm pieces welded to each other before the fitment to the wheelhouse. Note that the new panel was used as a template during the shaping work, Image 9.

Image 8 A part of the rusty wheel house edge is shaped in the Eckold Kraftformer.
Image 9 The new panel was used as a template during the shaping work.

The wheelhouse was cleaned up and the new panel was joined to the wheelhouse by full end to end welding with the TIG to the wheel house, Image 10. When cold after the welding the new edge was painted with primer, Image 11. The red one is conventional primer and the blue one is welding primer.

Image 10 The rusty part of the wheel hose has been replaced.
Image 11 Anti rust painting of the replaced part. Blue paint is welding primer, see the book, the red one is ordinary primer. Both are fast drying.

In the next step the new wheel arch was removed. How much can be seen in later pictures, note in this pictures that the door opening was removed. With the new panel reduced into a more practical size the outer edges was marked on the under lying wing with a marker pen. The wing was removed with an air driven grinding machine adapted with cutting disc. The margin to the marker pen line was approximately 10 millimeter, se later Images.

A part of the new panel had a less satisfying shape, the lower part with the same profile as the sill. There was some need of improvement and a new profile was made, Image 12. The profile was welded to the panel, Image 13. Here you can also see a non original improvement, a drainage channel. With this modification the vulnerable area can be dried up and the rust kept away for a long, long time if properly rust protected. The rust protection equipment was described in blog post 7.

Image 12 Folded profile for replacement of a bad pressed area.
Image 13 The new section welded and the weld is grinded down. Note the drainage channel.

Panel Beating Doctor Bengt Blad

At this point in my life when I was about three quarters through the medical schooI I discovered the English wheel and the Eckold machine, and, one thing leading to another - no more time for med school.

More about the book

This book, with around 1,500 pages of reader-friendly text and about as many illustrations, is a summary of 40 years of working with vintage, collectors' and racing cars.