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Selecting iron for brake drums

Just me, but I'd start with medium truck drums and modify to fit. I could find a pair of 14" drums, narrow them, skim the outer surface for the contracting band and be done before RFQs would be back from the foundries.

For instance Studebaker, Dodge and Ford 1.5t '50s trucks use a 14" ID drum.

If one just wants brakes, originality not withstanding, 12" ID trailer brakes are everywhere and can be made to fit and a 12" contracting band can be ordered from truck brake shops as many '40s-'60s trucks used external contracting parking brake drum on the rear of the transmission.

jack vines,
 
I'd love to start with a commercial part, but the mounting surface has to be practically right against the friction surface edge - in other words a 2" wide friction surface, and a completed drum that's a total of around 2 3/8" deep.
 
I know a guy who was doing that with a very specific brake pedal setup for a somewhat commonly built collector's car. Did decent selling them, usually came in little batches of sales. He wanted a setup for his own car, so he made some extras and ended up selling quite a few over the years.
That is 90% of all my shop does, make niche components for niche markets.
 
From over 40 years of experience using Durabar products, go find you some one like Windy Hill Foundry to cast you a pair of brake drums. He can cast them using a old drum for a temporary pattern. Durabar is good for many things but don't use it for brake drums or rotors. Such a large bar you're talking about using, it will only have a yield strength of around 20K psi if you're lucky. Most brake drums and rotors are much closer to a class 40 or even 50 gray iron. Which has at least double the yield strength you will ever get out of Durabar. Others may say differently.
I understand what you're saying here and in your follow-up post, but is their ductile not an option or are there other factors coming into play? Just reading on their site, the yield numbers come out a bit more than double that of their gray. I'm not questioning you here, just looking to get educated as to options.
 
I understand what you're saying here and in your follow-up post, but is their ductile not an option or are there other factors coming into play? Just reading on their site, the yield numbers come out a bit more than double that of their gray. I'm not questioning you here, just looking to get educated as to options.
I don't have a lot of experience with the 55-06 ductile they sell. Mostly in the smaller diameters under 3" OD. These run close to what 80-55-06 tensile requirements. The larger sizes I'm sure follow with similar results as the G-2 has but with ductility. These can be heat treated to get better tensile results if needed. If you go in this direction, rough out the parts before sending them out for heat treatment. The G-2 will respond to heat treatment, but you cannot temper it as you can with ductile iron. Not easily anyways.
 
i would definitely make this out of free machining steel.

in brakes gray cast iron is used most often, because it has the highest thermal conductivity. maleable is over 20% lower and ductile 10% lower still. "gg25" is popular, strenght usually is not of particular importance in cars (locomotives use ductile). however there are important details/secrets that make the particular alloys even more conductive and heat resistant.

(besides, designations like "gg25" are extremely broad categories anyway, defining one property only. it comprizes cast irons varying considerably in composition and even more so in structure and they might even differ from batch to batch.)
 
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Thanks dian for that reference - very interesting. It does seem to imply that gray cast iron, with lamellar or flake-shaped graphite, is a better choice for drums than nodular or ductile, with spherical-shaped graphite. I looked at a number of papers which model or test the thermal behavior of brake drums, and their samples are always gray iron. This may well be because that's what was available to them as commercial products, but even at that, it shows what the industry is choosing.
 
This is getting too difficult. If the hand/parking brake is on the ID then it likely is OK. I'm having a hard time rationalizing a lot of wear there. Check the ID and if it will be OK then you can shrink a new wear surface on the OD. You don't have to clean up the OD surface, just get a surface that will grip the Hoop that is being shrunk on. It would surely be adequate since you will not likely be dogging a 1911 car with 2 wheel brakes. Maybe some pics of what you have to work with?
 
The goal is to stay with a one-piece drum, but change from stamped steel to iron, for better friction and better heat management.
 
Hi kelfy:
You commented that the Paige has steel drums now but you want to go to cast iron for better driveability and better heat management.
So the car will be driven.

If the OEM brakes were pressed steel and you switch materials to any grade of CI, you are on your own as far as product liability is concerned, even if you adapt some other brake to your application unless you go through some kind of rigorous and legally defensible engineering study blah blah blah etc etc etc.

So unless you're prepared to do that, you can reasonably make it out of anything you want and the liability you embrace will probably be the same.

Setting aside the legal question, this is a 1913 vintage car...how fast and how far do you actually expect to drive it?
If CI is acknowledged to give you more of what you want, and if casting something is going to be hard and expensive, I'd just get the grade of Durabar ductile iron with the highest tensile strength, turn the bloody things and stick them on the car.

You know best of all of us, whether your use case will allow you to do so with a reasonable expectation you won't have a failure that trashes the car or worse, hurts or kills somebody.
Either way, from a liability standpoint, you're already in the shit up to your eyeballs if this thing ever crashes...even if the brakes were not the source of the problem, so if you've got the balls to accept all this, just buy the Durabar and start turning...it'll be fine...what could go wrong! :D

It'll be the cheapest, the fastest and no better or worse than any other choice.

Just as a reality check...I can buy a foot of 12" diameter ductile iron from McMaster for a thousand bucks give or take...not to suggest you should buy it there, but unless you build the pattern yourself, you sure ain't gonna get a patternmaker to make you even a loose pattern for that money, and since cast iron shrinks about 1/8" per foot as it cools, you can't just Bondo up the drum you already have in order to give you some machining allowance and go to town...there's more to it than that, especially casting a big, shallow, thin walled pan, like a brake drum.
Yeah, the foundry has to decide how to gate, vent, riser, and pour it, but if you don't give them a pattern they can use easily they will either refuse the job or charge you the earth to do them for you.
Either way, I predict you're not gonna get two usable castings for a thousand bucks.

Of course it'll be dirty as shit, to hog out all that ductile iron on the lathe, but you only gotta do it twice, and then it's done forever.
On a stout manual lathe you can do it in a day.
So buy and rig up a vacuum...a good one.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
Steel makes terrible brakes. That was one of Kosman's revenue streams, replacing steel with cast iron (meehanite in this case).
When one shrinks an iron hoop onto the steel drum, presto, iron friction surface. I hope he's not going to need enough braking to expand the hoop.
 
I'd like to get iron brake drums made for an antique car, 14" ID (2-wheel brakes). It has been suggested I start with material from Dura-Bar and get the drums machined out. I see that they supply 5 grades of ductile iron and 3 grades of cast. How would I choose what would give the best combination of lining friction and heat dissipation? Thanks...

Contact AlfaGT, highly likely he's been down this road before
 
Setting aside the legal question, this is a 1913 vintage car...how fast and how far do you actually expect to drive it?
Somewhat related .... had a customer named Scott Newhall. Along with 1890's paddlewheel steamers that he sailed across the atlantic, through the canal and up to the bay, he had a few old cars. Teens studebakers. He made sure they looked original but liked to do stuff internally, like electronic ignitions, modern pistons and higher compression ratios, better water pumps and so on.

So I delivered some parts one day and he said, "Let's go for a ride." I think this was the '17 ... got in, there's a nice stretch of freeway between san rafael and san quentin, these cars are not small. I'd say about fifteen feet tall and fifty feet long, when you're sitting up there on that wooden seat ... overlooking the 30" wheels that are about 2" wide.

These cars will easily do seventy. I guess the lack of brakes didn't matter because there was no tire to speak of anyhow.

How far do they go ? Scott used to drive the car to rallies but his friends kept giving him trouble - the old "what if it breaks on the way ? what if you get three flat tires and run out of spares ? what if what if what if ? You should really trailer to the event ! It's safer !"

So he finally gave in and told them he'd tow. Next event he kept his word and did tow - the '17 on a trailer behind the '13.

Some rich guy customers are too much fun, it almost makes up for the rest of them.
 
" I'd just get the grade of Durabar ductile iron with the highest tensile strength":

maybe read what i posted? you want (hypereutectic) ci with a low modulus.

as to steel: what are motorbike brakes made from? even ss. mild steel will perform not much different from ci, even with the same friction material. it will crack/deform in a high performance application due to thermal stresses.
 
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as to steel: what are motorbike brakes made from? even ss. mild steel will perform not much different from ci, even with the same friction material.
Maybe you missed where I mentioned that a major product for Kosman was cast iron rotors ? Back then steel was pretty common, the iron outperformed both steel which was stock on Harleys and maybe some others and the stainless rotors that the early jap bikes came with.
 
Hi dian:
You wrote:
"maybe read what i posted? you want (hypereutectic) ci with a low modulus."

Yes I get it, and if you were engineering this setup to make the best performing brake system possible, and had lots of cash and could find a foundry who could give you the material you specified and would certify to that, you'll get no argument from me...your design choice may well be the best possible...the safest, the best performing the strongest, the toughest...all those good things.
I don't know and I wouldn't dream of arguing with you about your recommendation.

But, and this is a big "but"...the OP is restoring a 1913 vintage jalopy and want's a practical choice he can get readily, and (I'm inferring here) something he doesn't have to put a pile of engineering and Quality Assurance and testing, and certification, and all that other stuff into.

My contention is he's taking a big liability risk just putting this thing back on the road.
He's taking an even bigger risk modifying things without an engineering analysis.

If he's willing to accept that risk, picking the very best material, although commendable (if it's practical), is almost pointless from a liability POV.
From an engineering perspective, of course you're correct...a better more suitable material is never a bad thing... but only if he can get it for a price he's willing to pay.
If he cannot do that, (and I don't know that he cannot but I certainly suspect so), then even casting his drums out of whatever grade of CI the foundry can conveniently provide is going to cost more and give no assurance he gets a better or safer outcome.

That's where I'm coming from...no dispute with your assertion that a hypereutectic CI with a low modulus is going to be a better engineering choice.
I'm just not confident he can find someone who'll cast only two drums for him and assure him in writing they've been made of that material...not for hobby kinds of cash outlays.

From a purely practical perspective, if he just bolts the original steel drums back on the beast, he dodges all that potential liability, but he says he wants "better" than what he can get that way, and is convinced some grade of CI is going to give it to him.
I don't know if that's true, but I'm certainly not gonna argue.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 








 
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