Posted By: reidy Drum maximum diameter - Wed Jul 01 2020 09:52 AM
Hello all

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.


Posted By: EdPruss Re: Drum maximum diameter - Wed Jul 01 2020 01:52 PM
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.

Posted By: 3B Re: Drum maximum diameter - Wed Jul 01 2020 02:25 PM
Hy reidy, .060" is the usual maximum oversize for standard car/light truck brake drums, hope that helps.
Posted By: Hotrod Lincoln Re: Drum maximum diameter - Wed Jul 01 2020 05:20 PM
.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.
Posted By: 52Carl Re: Drum maximum diameter - Wed Jul 01 2020 06:48 PM
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.
Posted By: reidy Re: Drum maximum diameter - Thu Jul 02 2020 07:12 AM
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.

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