Practical MIG welding - rear wheel arch repair

This wheel arch repair is part of a quick and dirty repair I'm making to an Austin Maestro camper van. I have a week to replace the bottom 6 inches of the car then re-paint the lower half.

The repairs themselves aren't to restoration standard, but I've included a few hints on how to make a better job.

The photograph doesn't do this wheel arch justice.

There are rust marks all around the wheel arch, and some really big bubbles in the paint. The bubbles are about 20mm diameter which is only possible with a really good thickness of paint or filler.

Also the shape is not consistent around the wheel arch. All of these things, together with the lack of metal to weld the end of the new sills on to, suggest a big wheel arch botch*.

Rusty wheelarch

With the paint and filler removed (with the help of a wire brush on the end of an angle grinder) the state of the wheel arch is obvious. It's mostly made of fibre glass.

Fibreglass and filler in wheelarcg

The car I'm working on is a van that has been converted into a camper. Unfortunately the only available replacement rear wheel arch repair panel is for the saloon version.

I decided it would be easier to buy the saloon repair section and cut out the bits I need rather than making the outer wheel arch from scratch. The wheel arch has been marked out for trimming.

Repair panel

I cut away the old outer wheel arch and found the inner wheel arch to be in surprisingly good condition. Normally the inner wheel arch will need to be repaired or replaced.

Actually, the condition was not perfect - the folded flange on the inner wheel arch was rusty so I cut it away. This means I'll have to weld to the outside of the new wheel arch panel rather than the lip on the underneath. I'll have to use a little filler to tidy it up afterwards.

Wheel arch cut away

It is good practice to use as little of the repair section as possible. This is so that someone else replacing the wheel arch again in 20 years time can use a little more of the repair section and be able to weld to the original metal rather than to your welds. Here I've just used the wheel arch itself and discarded the surrounding panel work.

I've gone for an overlap joint to the side panel to minimize the effort in cutting out and to help reduce distortion. Had I been replacing the front wheel arch I'd have taken the time to prepare for a butt weld as mud would become trapped behind an overlap joint and cause rust.

Repair section clamped in place

I should give the clamps a mention here. The clamps I'm using to hold the repair section in place are mini G clamps. These are available (from places like Axminster Tools in the UK) for about £1 each and have a maximum extension of 1 inch.

I only discovered then a few weeks ago and they have come in very handy. Their big advantage is their light weight doesn't put any real load on the panels to be welded so you can use as many as you like. I'm planning to buy some more.

Mini- G clamps

I've plug welded the outer wheel arch flange to the inner wheel arch and seam welded the repair section to the body sides. I've not made a continuous seam weld.

The area behind the wheel arch is inside the cabin so should stay dry. If the area behind the joint was wet then the joint should be fully seam welded. Proper restoration work would also require a fully seam welded joint to minimise the chance of bubbling in the future.

I've used a long steel ruler to make sure the weld to the side panel is below the level of the surrounding panel work.

WHeelarch welded in place

After grinding the welds down, a little body filler was required to achieve the correct shape.

I tend to apply the body filler using the normal plastic scraper, then smooth it using a steel ruler. The ruler removes any excess filler above the level of the surrounding bodywork, improving the shape and reducing the need for sanding. See the body filler page.

Smoothed with filler

The primer is a cellulose primer filler. It's a high build primer. I applied about 4 coats of the primer and then a thin guide coat consisting of body colored paint mixed with primer and lots of thinners.

The idea is to completely sand off the guide coat using 400 grade wet and dry paper. This ensures a smooth surface for a final primer coat and then colour paint.


A couple of colour coats were enough to finish the job. Doesn't she look lovely.

This is a "Tandy" Maestro Camper conversion (a pain as you have to take the cupboards out to do the welding). There's more about the van on

Repair completed

Next: Making a chassis repair section

*The word "botch" is derived from the surname of the engineer Thomas Bouch who designed the first rail bridge over the estuary of the river Tay. The bridge collapsed as a train crossed during a storm in 1869 resulting in the loss of 75 lives. This is why the rail bridge over the river Forth (started in 1882) became such a substantial structure.

Scotland's best loved poet, William Topaz McGonagall, had this to say about the incident: "So the train mov'd slowly along the Bridge of Tay, Until it was about midway, Then the central girders with a crash gave way, And down went the train and passengers into the Tay!".

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