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Drum maximum diameter
#1367289 Wed Jul 01 2020 09:52 AM
Joined: Jan 2010
Posts: 32
R
reidy Offline OP
Wrench Fetcher
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.

Thanks

Steve

Re: Drum maximum diameter
reidy #1367300 Wed Jul 01 2020 01:52 PM
Joined: Jun 2011
Posts: 3,612
E
Shop Shark
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.

Ed


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
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Re: Drum maximum diameter
reidy #1367303 Wed Jul 01 2020 02:25 PM
Joined: Nov 2005
Posts: 5,751
3
3B Offline
Master Gabster
Hy reidy, .060" is the usual maximum oversize for standard car/light truck brake drums, hope that helps.

Re: Drum maximum diameter
reidy #1367336 Wed Jul 01 2020 05:20 PM
Joined: Feb 2004
Posts: 20,868
H
Boltergeist
.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.
Jerry


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Re: Drum maximum diameter
reidy #1367342 Wed Jul 01 2020 06:48 PM
Joined: Mar 2010
Posts: 9,401
5
Master Gabster
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.

Re: Drum maximum diameter
reidy #1367425 Thu Jul 02 2020 07:12 AM
Joined: Jan 2010
Posts: 32
R
reidy Offline OP
Wrench Fetcher
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.

Steve


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