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Old 08-25-2016, 03:52 PM   #1
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Where are the Specs for Brake Drum Thickness?

Purchased a 68 Tradewind 24 and am trying to get it to pass safety inspection in Maryland.

The guy inspecting says that I need new brake shoes due to wear and also that he cannot determine the make of the brake drum from inspection so that he can check if the steel thickness remains within safety tolerances.

I have searched in vain for any reference to brake drum thickness. I suspect that these are the original brakes. Don't mind replacing the backing plates but I would rather not replace the drum (and bearings).

I live near Annapolis. Any thoughts about what to do?
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Old 08-25-2016, 05:00 PM   #2
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Lots of drums have it stamped on the face.
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Old 08-26-2016, 03:11 AM   #3
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Where are the Specs for Brake Drum Thickness

Thank you. The mechanic said that he couldn't find a marking. Don't know if there is one--I supposed the marking could be obscured by surface rust.

The mechanic said his best guess is that the manufacturer he thinks it might be is out of business--which still leads to question as to where is the spec. for drums in general?

I'm somewhat surprised this issue hasn't come up in forum postings before. Are Maryland inspectors the only ones who look for thickness on brake drums?
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Old 08-26-2016, 05:30 AM   #4
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BTW... in NYS if the drum isn't stamped for max internal diameter it can't be failed. I had the same concern when getting our 53' Ford inspected, do the google on your State insp regs to confirm.
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Old 08-26-2016, 12:39 PM   #5
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Minimum drum thickness should be cast into the drum.

Q's: Do drums actually need machining?? Does shoe arc match drum arc??

To correct shoe arc: Shoes can be arced at an old school friction supply company. Back in the day, shoe arcing was done all the time.

When you take this route, bring drums with you. Shoes need to individually arced to custom fit each drum. When arcing is done, you have a shoe-drum "matched set."

I hope this makes sense.

Tom
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Old 08-26-2016, 11:57 PM   #6
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Normal is .060 of an inch over. So a 12" drum shouldn't exceed 12.060" when measured. It is common to push this a bit but if it's going to be inspected, maybe not. Brakes stop you by turning the motion into heat so the less metal there is in the drum the more likely you are to have fade or warping.
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Old 08-27-2016, 01:43 AM   #7
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Quote:
Originally Posted by TomKirk View Post
Minimum drum thickness should be cast into the drum.

Q's: Do drums actually need machining?? Does shoe arc match drum arc??

To correct shoe arc: Shoes can be arced at an old school friction supply company. Back in the day, shoe arcing was done all the time.

When you take this route, bring drums with you. Shoes need to individually arced to custom fit each drum. When arcing is done, you have a shoe-drum "matched set."

I hope this makes sense.

Tom
Quote:
Originally Posted by ijustlee View Post
Normal is .060 of an inch over. So a 12" drum shouldn't exceed 12.060" when measured. It is common to push this a bit but if it's going to be inspected, maybe not. Brakes stop you by turning the motion into heat so the less metal there is in the drum the more likely you are to have fade or warping.

Hi, shoe arcing was made illegal decades ago and the machines were scrapped. Turning drums to a max of .060 is pretty common, but as in Bob's picture, .090 is the limit on some Airstream drums.
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Old 08-27-2016, 06:16 AM   #8
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Maximum diameter will be 12.090 for most 12x2 drums.
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Old 08-28-2016, 06:13 AM   #9
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Thanks to all. In talking to the mechanic, he eventually was able to find out about the internal diameter spec. Problem solved, I do not need new drums.
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