The Stovebolt Site Forums The Shop Area General Truck Talk Minimum Thickness on Rear Drums?

Does anyone know what the minimum thickness is on the rear brake drums (very likely stock) for a 1946 3/4 ton?

I think that mine are shot, but I'd like to know for sure. There's a pretty good lip at the edge thats gotta be about a 32nd of an inch high on both of them, and they're pretty scored.

If I can get 'em turned, I will. Otherwise, I'll start looking at finding some replacements.

Any advice is appreciated.

brendanm720,

I would think a 32nd would be very minor. Unless you plan on running at Indy, the drums don't have to clean up 100%. It sounds to me like they would work fine.


Stuart

if you still use the truck for work (i.e. hauling big loads), i'd recommend tracking down some better drums with a little less wear. not an easy task but safer if you're bringing a big load to a stop.

if you're using it just as transportation, you could probably get by with cleaning them up a little and putting new shoes on.

one thing i found when i was working on the rear brakes on my 50 3/4 ton was that i couldn't find a shop that would even clean up my existing drums because they were out of spec. liability issues for them so they wouldn't take the responsibility.

look for a bone yard in your area and see if they have any less worn drums. i had to go through about a dozen drums and pick the best two. most 3/4 tons were really used for work trucks so they seem to have taken more abuse than 1/2 tons.

good luck and i hope you find some good ones!

The general rule of thumb is to replace drums if they're .090" over standard diameter. You might get away with .125" over (1/8") if you can get any machine shop to turn them that far. Most won't because they're violating federal laws (DOT rules) if they do. Nobody is going to put his business at risk so you don't have to pony up for new drums.
Jerry

Thanks guys.

I am already planning on putting all new shoes on all the way around. The front linings aren't in the best shape (and they're not exactly still attached, either).

It will be my truck for when I need to move something large, but it won't used for that very much, and the loads won't be heavy too often. It will primarily be a driver for on the weekends or if my regular car is in the shop.

Could someone refresh my memory as to what years I could use as a replacement?

Thanks in advance.

Yup!

Typically, on modern drums, max machine is .060 over stock. This gives you .030 for final wear. After that, the drum may work but, eventually, issues of the wheel cylinder working past design and heat build up from thinner drum material will be something to worry about amongst other things.

Except for some weird drums put on late 70's to mid 1980's GM trucks and SUV's and a few others, most all drums were done in even numbers. So if you have a 12" drum, max machine will be 12.060, discard 12.090.

Of course, I could be wrong about them little drums. Lately I've only been working with the 15" to 20" drums ( big trucks.) Tolerances might be greater for those smaller drums. I'd have to look up the specs on Monday.

Personally, if I had drums in the .060 to .090 range, I would go ahead and turn them. Especially since, generally, only .010 is removed. Considering that I would have a brand new set of shoes with max material on it and the brake wasn't seeing daily / constant use, I would feel comfortable with the setup.

Don't forget to lube the wear pads behind the shoe. Make sure they are smooth, too.