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.
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.
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.
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.
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.
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.
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.