32-34 ford brakes drums

Every modern drum I have ever turned has been stamped “maximum .060” over, or it has an actual discard specification.

I have all kinds of original early Ford brake literature and nowhere does any of it mention machining brake drums or maximum oversize limits. I even checked an old Motor’s Manual and they do not even discuss brake drum inspections???
Years back, some guy wrote in the Early Ford V8 Times that the drums could be safely turned to .100 over but I have no idea what he was basing his info on? I would think .060 would definitely be safe and .100 might be pushing the limit.
 
I had a '34 sedan that the brakes were found to have been turned +3/16" (0.187")! It still stopped, after a fashion, I guess because they had an extra set of linings bonded to the shoes.

When I discovered this, I swapped them out for some good, uncut drums (and matching shoes): when examining the old ones I could actually see daylight through a section of one of the rear ones, where the machining had broken through!
 
The problem is that the brake drums heat up very rapidly when they are turned too thin. As they heat, they get bigger meaning that the shoes have to travel further out resulting in the pedal going closer and closer to the floor. They may stop you fine running around town, but don't dare drive down a long hill at moderate or higher speeds!
 
I adhere to 12.060" because my understanding is that unless cast into the drum otherwise, that is the maximum safe and/or prudent limit. The new USA drums have a maximum on them of 12.090" which means that they are thicker to begin with and can be machined more, although most of us will not ever wear them out... In addition to the heat buildup issue, there is also the issue of "cross-section thickness" where the shoe surface adjoins the drum face. I heard about a guy (supposedly had a bow-tie pickup?) who had machined the drums waaaaay out beyond. He had to make a hard stop one day on the freeway here in Southern California (where all the brakes you can buy are essential...) and all four shoe surfaces supposedly sheared off of the drum faces. In my searches for good used drums, I have found some that had been run at 12.200" which is insane. No matter what the book says (I know I saw it somewhere) the thicker the better, with the fronts being more critical.

I have some good used/usable 32-34 drums that were removed when converting to hydraulics. Good fronts are scarcer than good rears.
 
Some guys will turns drums until all the bad spots are cleaned up, check them to make sure they are not oversize but they do not match the diameters of the drums on the same axle. You should keep the drum diameters on the same axle within .010 of each other, otherwise they will not brake evenly and will pull to one side. Drum brakes are real finicky compared to discs.
 
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