Re: Thoughts on how to fill pinholes in a disk brake backing plate...

Posted by HH56 On 2017/9/26 17:32:18

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.