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Hi,

I have a general resto question... This is for a disc brake backing plate. ...so think 20-22 guauge sheet metal. The plates were in the junk yard and have rusted thin. ...rusted thru in some areas, and pin holes in others. I can't get replacements. I am bout to bead blast them. ...hopefully there is enough good metal left for that!

So I figure that my options are leading, lab metal and/or possibly soldering. I plan to prime and paint them afterwards. Any thoughts or suggestions?

There is too much contour to completely re-fab replacements.

Thanks,

Mark

Assuming it is just a fill coat for pits to provide a smooth finish so no strength is required, then as it is not structural and if the metal is clean with all rust killed with some kind of treatment, I think I would go for the lab metal.

Something like steel reinforced JBWeld would work or Bondo makes a steel reinforced filler. Either could be skimmed on and sanded smooth much easier than lead or solder could be finished and would probably adhere just as well.

If the plate flexes probably the Bondo would be the more likely to flex with it. The Bondo says it can be drilled and tapped but I have no experience with it's strength.

If there was some minor reinforcements or thickening of rusted away areas required I would probably opt for a combination of maybe brazing or silver solder for strength and a thicker layer of tried and proven JB Weld as a smooth coat. I don't think there would be as much strength with lead fill but I could be wrong.

With any heat I would be worried about warping the flat sheetmetal so that would need to be carefully watched. It might even be better to bond on a reinforcing plate rather than try to use heat.

Yes, to be clearer, I am looking to give it some strength back.

I did think about the lead further and figured that with the amount that I would use, I would be melting the stuff that I just put on, as I go.

I'm not sure that it could withstand the heat of brazing either.

I did think about JB weld. I think that I have some of that around. ...somewhere.

My fallback would be rusty metal primer and Rusto over that.

What year and model P are you talking here? Some outside company made those brake parts, so you may find elsewhere.
There's always parts, if you're willing to search and pay.
When a piece is stamped out, it's often difficult to repair to resto quality. But can usually be done, just takes a long time to fit, weld, and finish so it doesn't look like it's repaired. So the cost of parts is a big savings in time.

por15.com/Putty-Fillers-Undercoating_c_15.html

Either the patch or the putty