Suspension patch & repair

[Doive]

Long story short - one of my rear spring pans cracked this morning and fouled the wheel. Surface corrosion has weakened the outside of the pressed steel member, and the force of the spring has deformed it slightly. I managed to hammer it back to shape and drive very slowly 800 yards to a safe place. Planning to get the car recovered home. Question is - would it be safe to weld the spring pan? I was thinking grind & wire brush cup all the rust out of it, treat, and then plate round the weakened areas with 1.6mm or 2mm plate. Is that realistic?

Also, to add to my joys, I picked at an area of loose underseal, and discovered a spot of further corrosion above the top spring mount. It's not too bad, and a small patch will sort it. Around the top and sides I will lap and seam weld. The lower edge is a thick return piece from the chassis leg - I was thinking of plug welding this every half inch or so. Or should I seam it all round?

 

[octo0072000]

seam weld it all round for a MOT point
might be better to cut the lot out remake it on the bench then weld it back in if the spring seat has gone

 

[BillJ]

Hi, Doive! The original inner wing is spot-welded to the spring seat so while you're right that the MOT will require the repair panel to be seam-welded to the inner wing (to make it effectively a single panel as it was when it left the factory), the spring seat can (and should) be plug-welded, equivalent to the original spot-welds.

Honestly, I would replace like-for-like. You'll probably find it's about 1mm for the inner wing. And as Octo says, you might want to look into the feasibility of re-making the spring seat or part of it. And try very hard to get rid of as much rust as you can. Rust treatments and converters are nowhere near as effective as the manufacturers would have you believe.

The problem with going over-thickness on repair panels is that the new panels will flex less and put more stress on other parts of the original structure. This can lead to fatigue, often at the welds.

I notice my dad's 9000 has a little bit of underseal lifting in that spot (nothing as bad as yours ) and I think I'll have a closer look now, so I have a vested interest in you proving a decent repair

I've never looked very hard at that part of the car. I assume it isn't accessible from above?

[Edit] Reading again, are you saying you have a problem with the lower spring seat on the trailing arm as well? If so, simply replace it rather than repair. Try to make sure the donor is from a bit farther south. In my experience, Scottish cars suffer far more from rust than those down here.