Maximum diameter of cast iron drum?

7_Zero

7_Zero

Senior Member
What is the maximum allowable diameter of cast iron brake drums?

My brakes were pulsating so I had them turned, they ended up being 11.060". Everything that I found here on the barn states that the limit is anywhere from .060"-.070" so I decided to get some new drums. The new drums arrived and they are already .065" over. I called the supplier and they said that it was fine as the new cast iron drums are thicker and can be turned .195".

If this is correct, I just wasted some good drums! If it is not, then I just received some drums at their limit. Any insight would be appreciated, thanks!
 
Did you already scrap the old drums?
I would have no problem using .120" over on cast iron drums.
Have you checked the accuracy of your measuring tool?
It does seem strange that new drums would come oversized.
 
Something is getting lost somewhere. Not knowing better I would assume the limit on the original cast iron drums is .060. The new cast iron drums are thicker and I believe they are marked .090 max (not .195) but will stand corrected if someone has one to look at. Don't go by what I say, read what it says on the drum. A good set of new drums should be slightly less than 11 inches to allow for a clean up cut after they are mounted. If someone sold you a set of drums .065 over representing them as new I would suggest you return them. If they won't take them back after you ask them to do so, check to be sure all of your facts are correct and then post who it is to protect others.

Charlie Stephens
 
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I don't like cutting smaller automotive/car drums beyond .060". If the maker says they can go more than that, then fine. But, I'd feel nervous about it.
 
So who is the supplier? If you trust them for their product quality, and they tell you what is the acceptable oversize tolerance, I would run them.
 
Did you use a brake drum micrometer to measure the drums?

Bob
 

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I was under the impression that new cast iron drums are actually under sized (under 11") and designed to have them turned, if using original hubs, to true the drum to the hub; you should end up very close to11" inside measurements which allows you to use stock size lining on your brake shoes; your last operation would be arcing the shoes to the drum ?

If I am wrong please let me know.

Ron
 
Charlie Stephens said:
The new cast iron drums are thicker and I believe they are marked .090 max (not .195) but will stand corrected if someone has one to look at. Don't go by what I say, read what it says on the drum. A good set of new drums should be slightly less than 11 inches to allow for a clean up cut after they are mounted.

Charlie Stephens
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I have a new set of Bratton's Rear cast iron drums sitting here. I don't see any Maximum size marked on the drum but they are marked .008" and .010" for clean up after being mounted to the new hubs with new hub bolts.

IMO .065" is too much for clean up.
 
Ron in Quincy said:
I was under the impression that new cast iron drums are actually under sized (under 11") and designed to have them turned, if using original hubs, to true the drum to the hub; you should end up very close to11" inside measurements which allows you to use stock size lining on your brake shoes; your last operation would be arcing the shoes to the drum ?

If I am wrong please let me know.

Ron
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Your right on
 
Ron in Quincy said:
I was under the impression that new cast iron drums are actually under sized (under 11") and designed to have them turned....
Click to expand...

This was my impression as well, so I was surprised when they were not 11".

I did use a micrometer, in fact it is the same one Bob posted. I just had a shop double check my measurement today and they came in a little over 11 1/16" which is about .062" so my mic looks accurate.

I got the drums from Burt's so needless to say I am very surprised they are over as much as they are.

I have looked over the drums and cannot find any imprint on the drum indicating its maximum diameter. Where is this usually stamped?

Also, one of the drums has pits in the inner edge of the contact area, is this something to be concerned about?

Thanks!
 

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Did these drums come from Burts like that, or, where they cut by someone else ?

I don't like that row of pits.
 
I'm not that much of a car mechanic, but would they have turned the drums trying to remove the imperfection/pits??
 
I must say that I am a little confused. Can someone clarify, please? I had always thought that the issue was what the wall thickness of the brake drum was, not necessarily the inside diameter. Obviously, the I.D. matters within a certain tolerance range, but I have never heard of a brake drum being discarded because of an oversize I.D., only for a wall thickness that was too little. Educate me here? Thanks!
Chris
 
I put a set - all four - of AR drums on my 28 pickup about a year ago. They has no markings on them when I started. They were - all four - .010 to .015 under sice and had to be turned to exactly 11" dia on the inside after the hubs were swedged on.

I have installed severl sets of the Mel Gross drums on customers cars and never seen any markings on them indicating diameters. They have all been 11" from Mel (now Randy). After swedgng the hubs on they are returned to get then True Round. Usually .002 to .005 has to be turned go get then perfect after swedging. Never more than .005

I installed a set of hubs on NOS Plasmeter drums last week for my own project,. Again no markings. Hubs swedged on and then turned. The brake turner - not me - had to turn off .020 or more to get then down to 11" inside diameter. He has only turned the front drums so far. The rear drums , unturned - measure 10.080.
 
I'd have rejected that drum with that many pits, or at least have sold it as a second for a much reduced price. If the air pockets were due to a cold pour I'd reject it.
 
It seems like you received defective drums so just have those replaced at no cost. No big deal and nobody's fault these things happen..

Those pits are an issue also
 
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Greg,

To clear up a couple things here regarding the brake drums we installed for you.

A few months back we switched to Brattons drums, since the nodular iron they are made from is designed to last longer then the Snyders drums we used to use. These drums you have are Brattons drums. The flaw in the Brattons drums ,is the ID BEFORE they are trued is 11.030. The Snyders drums are 10.980. Since the drums are larger ID, they must be trued around .020-.030 , which makes them larger OD. We may switch back to Snyders drums , since they are 10.980 before truing. Many, of both manufacturers drums, have small air pockets in the casting, which are viewed in the above photo.

If you would like us to re install new drums on your hubs, we will do that for free, and if you want the smaller Snyders drums, then I can get some of those and put them on instead.

Regarding your old drums. We spoke yesterday about them, and I was confident, but not sure, that they were steel drums. We removed them , per your request, to replace them, and threw them in the scrap trailer, which we took to the scrap yard last Monday, since it was full. I did not look at the drums in the scrap trailer, since there were around 50-60 of them in there, that we had removed from other drums we removed and installed for other people in the last few weeks. So, since you wanted them removed, we threw them away.

I will talk with Brattons next week,and see why they make these drums larger ID. I had not noticed this, but it does make them easier to install, as the biggest complaint we had on the Snyders drums, was we would true them to exactly 11.000, and most folks had a hard time getting them on the shoes (particularly the rears).

So, let us know what you want to do. I can send a call tag to pick them up, and we can solve this any way that works for you.

Steve Becker
Bert's Model A Center
 
I guess if customers don't fit their shoes to the drums they will have a hard time. We have been using Snyders drums for a while and yes after mounting on the hubs they have to be trued and sized to 11 inches.
 
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