Brake Drum Thickness

Leathernek

Leathernek

Senior Member
What is the original thickness of the steel front and rear brake drums? How much can you turn them before you have to have them replaced? Tried searching the forum and Andrew's book with no luck......

thanks,

Josh
 
I searched as well and there used to be results that would come up under that search. I was going to supply you the link. If memory serves, and I’m at work and don't have my reference material. Stock thickness was 0.140" and the thinnest you should safely run them is 0.110" or just under a 1/8" thick. I have seen them run thinner but I wouldn't recommend it.
 
Call your local brake shop and ask if there is a law/practice on how far they can turn them. I think .060 on the diameter is max in California (meaning 11.060 on a Model A drum) unless otherwise marked. This means regardless what the thickness is, the max is .060 on the diameter.

Charlie Stephens
 
Charlie Stephens said:
Call your local brake shop and ask if there is a law/practice on how far they can turn them. I think .060 on the diameter is max in California (meaning 11.060 on a Model A drum) unless otherwise marked. This means regardless what the thickness is, the max is .060 on the diameter.

Charlie Stephens
Click to expand...

I took my 91 Olds front rotor in to a local parts store to have it turned for a slight pulsing. They told me it was too far gone. My dad bought the car new and replaced the rotors shortly before he passed and I knew they were plenty thick, so I went down the road to a good brake shop and had them turned for $10.

As mentioned I think .060" over on the rolled steel drums is about the limit.
 
Yes, I should have explained it that way, I’ve worked in Machine shops for years and 0.140" - 0.110" is a difference of 0.030" on a radius, or 0.060" diameter. So 11.060 is the largest you should go on the steel drums. I don't know about the new iron ones.
Thanks for clearing up my answer guy's. lol
 
When I see that ".060" is mentioned as the legal limit I was curious, in looking at the wording in state laws I find that an actual size is not mentioned, just "manufactures" specifications"

---an example of brake drum "law"-

6. Brake drums or disc brake rotors must not be contaminated in such a manner as to change the frictional qualities of the friction face or show mechanical damage to the friction surface other than wear.
7. Brake drums must be free of any external cracks, except when the drum is properly banded to prevent the crack from expanding to any degree upon the application of brakes or otherwise. Any bands so used must be free of cracks.
8. Brake drums or disc brake rotors must be free of any substantial cracks that reach an edge of the bore of the drum or periphery of the rotor.
9. The diameter of the brake drum at any point must not exceed the manufacturer’s allowable maximum, discard, diameter.

It is sometimes hard to find the spec, .060 is a common american spec for 50s, 60s, 70s brake drums, but some are .080, some .030, and I have also seen .187 as a spec on a drum---I think 1971 is the first year the drum itself had to be marked with the max size

For the model A --on page 514 of the service bulletins it says---

"Under NO circumstances must any attempts be made to turn down brake drums on A cars and AA trucks."

Therefore if the manufacturers specifications are used it can be reasoned that ANY turned A drum is not legal ---

When I was looking for drums I made a gauge out of brazing rod --2 piece 1-6",1- 5.020, another 6.020 --I was looking for some 12" drums for a 36 also.
i figured that I didn't want any drums over .030 if I am to have "good as new" brakes, the .040 drums went out of round quick on the front. ---
 
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