My shop was inundated by the Harvey flood (Galveston County Texas). I was just out in it today and picked up one of my backsaws.
It is a Disston D-4. The saw plate has grunge on it that I will never be able to make go away. It has a sound handle and needs to be
re-finished. It is 14 tpi filed crosscut, sharp with fine uniform set, but not pretty. I put a scrap of quarter round in a bench hook and
sawed an inch off the end and it cut smoothly, quickly and left a smooth end.
I do not remember setting or sharpening the saw. If I set it, it would have been a screwdriver set. If you have never done a screwdriver
set, you should learn to do it. I have Lie Nielsen back saws, but the old D4 is equal to them. If you run across a D4, pick it up. You will not
be disappointed, it just feels right when you use it. It has mass to it and tracks true.
OBTW, sand paper, steel wool, and Johnson's floor wax does a good job of de-rusting but will leave grunge.