Help with rear arches.


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New member
May 13, 2021
Hi All.
A year and half ago I had a lot of welding work done. As the puma was sat for 5 years. I had the rear arches also welded up and painted. About 2 months later bubbling appeared. So I sanded down the arch and painted it my self. Then in October the bubbling was back and I had to re-sand the arches and paint them again.
In February I had a full car respray done due to the lacquer on the car going off. And they sanded the arches down, but today I’ve found they have started to bubble again. Behind the arch is all seam sealed and under sealed.

The car doesn’t have carpet arch lines in, I removed them when the welding was being done and I’ve never put them back in.

Any advice to what could be causing them to bubble up this fast ?
Might be a silly question, but were the arches treated with rust converter before any paint went on. Despite them being sanded down you should still treat them as any rust even not visible to the naked eye could set them off.

Also, make sure the inner part of the arch lips are 100% clean, sounds silly again but they are exposed to the elements & are susceptible to accumulating a lot of crap which increases corrosion even quicker than the outer surfaces, so extra prevention in those areas is advised & regular cleaning out thereafter. If these are the areas you are referring to that you said are seam/undersealed then that "should" have been enough.

I would then be checking inside the car behind the rear trim panels & treating them well as they are a known cause too.

Here is a thread that goes into detail regarding rear arch rust prevention which may help:-

Good luck :eek:k:
I'm currently tidying up the rusty rear arches on my Thunder, not worth having the arches replaced, so ground out all the rust I can find, treated with Dynax S50 rust converter, then several coats of zinc primer, used waterproof filler, then lots of primer. It should tidy it up for now, but I don't expect it to last !
If it was my MSB low mileage one, I'd have the arches replaced, as that'd be worth spending the money on.

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