Heya folks I have a 4x4 E350, 1996. Posting here as the front axle is 96 Dana 60, ala the trucks. 4x4 conversion was done by Quickly when the vehicle was new.

I'm in Ecuador with the vehicle and we replaced the discs and pads. Only pads we could get were semi-metallic. Then 5-8k miles later we were checking everything and the pistons were disintegrating under the little steel heat shield. So a mechanic found us pistons and we replaced all 4. However they wet sanded inside of the caliper in the piston bore as one piston seemed reluctant to go in. Then driving in the mountains I had a brake start dragging. Took the wheel off, it was plenty hot, let it cool down, pushed the piston back in, brakes behaved OK after that... was the same piston they had sanded. Now at a mechanic for another issue and we started looking at the brakes in more detail and the piston that had been problematic is crumbling under the steel shield, only a few hundred miles after replacement. Presumably the heat when it dragged damaged it quickly, or it was a POS part, or both.

Questions- are there significant differences in piston quality?

Is it likely that the semi metallic pads add enough heat to damage pistons?

If the caliper is warped is it realistic to sand the piston bore and get it working well or should I look for a new caliper (which could be very hard to find here)?

Is it possible old/poor brake fluid could contribute to this?

Thanks in advance for opinions, they are much appreciated...

Josh