I have a pair of front drums of a 1942 Chev 3/4 ton truck. I would like to have them machined but I need to find out what the service limit for these drums are.I know all newer drums have this cast into the drum. If a limit was never specified what is the general consensus on the limit for these drums?
I know I can buy new ones but being in Australia the freight will most likely cost more than the drums.
How do you know they need turning, might be best to try them out first since they are so hard to find. Many shops here just turn everything as a matter of course, not considering they might be hard to get.
Hy reidy, .060" is the usual maximum oversize for standard car/light truck brake drums, hope that helps.
.060" for passenger car drums, and .090" for most light trucks was the rule of thumb back when I was making a living doing brakes. You can get by with slightly larger dimensions if you grind the linings to match the radius of the drums, but don't make it a habit of hauling heavy loads if you do that. Since most brake shops refuse to grind linings any more, a shade tree method that works well is to glue a piece of coarse sandpaper inside a drum and scuff the linings to a good fit. Using water-soluble glue on the sandpaper makes it easier to remove with boiling water when you're done with the fitting job.
With the scarcity of these drums, I would only have them turned if they where horribly scored (probably not salvageable if that were the case) or not round. A little bit of scoring will not affect braking, as the shoes will form fit to the grooves fairly soon.
Thanks for the replies. The ones I have are currently .070 oversized and are mildly scored and well weathered. There is a shoulder at the top. I will give them a cleanup and de-rust.If they can have the worst bits knocked of and come in at under .090 I will be happy to use them.