I have a decent pair of '40 front drums that measure 11 15/16" inside lining to inside lining with a tape measure. I want to know what the stock original inside measurement is from the factory, and how much material can you safely remove to clean them up?
Your wording is a little differenet so I will answer in my own words. The inside diameter of the '40 Ford drum was 12.000 inches. Ford didn't have a spec but the accepted max is usually 12.060 diameter (unless otherwise marked, some newer replacements are marked 12.090 max). Charlie Stephens
Thanks Charlie. I guess I need to take them to a machine shop to be measured accurately....note to self...never trust a tape measure.
Larry any shop with a drum lathe should have a drum gauge that you just set to the right diameter and stick in the drum to measure it.
If you've seen lots of Ford drums, it should be easy to spot the ones that are way oversize, just looking at the thickness. The best way is to have a new shoe handy to set inside the drums to see if the curve fits, or does the shoe rock like a rocking horse.? If it rocks at all, it's probably over specs, and you will go thousands of miles before it ever seats in, to get a full wear pattern and stop better....or get the shoes re-arched to fit the drums. Old cars are fun
Size does matter in braking efficiency , we had four used f100 drums machined with new radiused shoes to match the drums. Never really stopped great , kind of pedal went away with moderate pressure. Measured the drums and all were approx 3/16 over stock dimension. So drums were growing with braking force. Fitted new drums and it's like night and ay as far braking and peal feel. So don't always trust the brake shop to get it right.
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