Spec for machining brake drums

Started by Gary Vickery, January 04, 2025, 02:49:42 PM

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Gary Vickery

49 Plymouth (long ago)
35 Plymouth PJ Deluxe
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TodFitch

#2
I have never found that information in the early 1930s service manuals. I understand that some brake drums are marked with the maximum they can be turned but, again, I see no sign of that on my drums.

From what I have read and from the adjustment range of my AAMCO brake adjusting tool, I think 0.100" is the absolute maximum. I am not sure about the '35 PJ drums but the '33 PD drums are scarce as hens teeth and my opinion is that the less the drums are turned, the better. I'd rather have a little pulsing on the brake pedal than a drum that is so thin it overheats easily or becomes bell mouthed.

By the way, if the drums are not standard size then the brake shoes should be arched to match the drum they will be in. If you don't arch them it will be impossible to get them adjusted properly and you will have poor braking performance until the shoes wear in. I used a roll of sticky backed sandpaper from my local hardware store. The steps I used were:

1. With the drum off the car. . .
2. Cut a strip of sandpaper to the circumference of the inside of the drum.
3. Stick the sandpaper to the drum so that the abrasive side faces the brake shoes.
4. Mark the face of the brake shoe lining with so that you can track progress.
5. Rub the brake shoe around the inside of the drum until the markings you made are erased and the shoe uniformly contacts the drum along the whole surface of the lining.

Each drum will be slightly different which means that the shoes need to be installed with the same drum they were fitted to.
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Gary Vickery

I want to get my brake drums turned on my PJ, both to take out some small ridges and to ensure they are circular.  How far can they machine the drums?  What is the max diameter?  I can't find that info.  Thanks!
49 Plymouth (long ago)
35 Plymouth PJ Deluxe
  •  

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