Brake drum thickness measurement and with micrometer questions

[12secvx]

Ok I just turned a set of 35 front drums that were rusted. And I measured them after turning them at work. To see if they were still useable. I guess I have wishful thinking that they may work 10k on my Model A sedan. My question is when the spec is .060” maximum that can be machined off doesn’t that actually translate to .120” overall ID? .060” off the braking surface? Mine measure 12.16” - 12.14” ID with a thinkness messured between the ribs of .100” thinkness remaining. I know thin and would replace them but they are 35’s and are hard to find good ones for a decent price and even decent price for shipping once you find some. Ben

[skidmarks]

Isnt a 35 the same as 32 to 34 drums?

[Fordors]

The .060 dimension is the maximum oversize allowed, the biggest cut can only be .030. I think I might try them if they were rears, but it sounds pretty sketchy for the front brakes, those do most of the braking.

[Kube]

Originally Posted by 12secvx

Ok I just turned a set of 35 front drums that were rusted. And I measured them after turning them at work. To see if they were still useable. I guess I have wishful thinking that they may work 10k on my Model A sedan. My question is when the spec is .060” maximum that can be machined off doesn’t that actually translate to .120” overall ID? .060” off the braking surface? Mine measure 12.16” - 12.14” ID with a thinkness messured between the ribs of .100” thinkness remaining. I know thin and would replace them but they are 35’s and are hard to find good ones for a decent price and even decent price for shipping once you find some. Ben

Legally, at least here in WI. your drums are illegal. 12.060" is the maximum. And no, that doesn't translate in to anything other than 12.060".
Yours being .100 over would scare the heck out me.

[Bob C]

When the spec is .060 that means the max drum diameter is 12.060.

[12secvx]

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Unfortunately that is what I wasn’t wanting to believe. .030” Isn’t much at at all that would most all used drums unusable.i though on mechanical brakes you set them up where the rear does a majority of the braking. I’m not
Sure if 32-34 are the same?

[12secvx]

So I was looking for the new measurement of 35 drum and it is exactly 12” or is there a variance?

[Karl]

Originally Posted by 12secvx

So I was looking for the new measurement of 35 drum and it is exactly 12” or is there a variance?

Exactly 12" -You would be surprised - My second hand front brake drums Measured exactly 12" I guess its the linings that wear rather than the drums.
Karl

[deuce lover]

Originally Posted by skidmarks

Isnt a 35 the same as 32 to 34 drums?

Shoe width on the 35's are 1 3/4" and 32-34 are 1.50"

[51woodie]

The comments on the amount that can be removed are correct, 12.060". The thing that was not mentioned is the fact the brake shoes need to be "re-arced" to match the drum I.D. after machining. When I was in school taking auto mechanics, any time we did a brake job (all drum brakes at that time) and machined the drums, we would put the shoes on the arcing machine so they would match the respective drum. Old school. I had to "hand fit" my new shoes when I did my '46 last summer. Granted, the shoe itself is supposed to flex a bit when applied, but if arcing is not done, the braking capacity will not be there. If you are in doubt, set up your brakes, take a short drive at slow speed while applying the brake several times. remove the wheels and drums and check for shoe contact.

[12secvx]

I’m aware of arching shoes to fit drums. I guess I’m in the market for a new used set of front and rear 35 drums. Darn it this just got very expensive

[Flathead Fever]

.060 over is the maximum allowed on any car drum. They are trash at that point. When they get too thin they will flex when the brakes are applied. They could overheat and get warped when the brakes are applied.

When you machine them you need have enough material left to account for the wear from the current brake job. Maybe you would not want to go past .050 so that during the life of these new brake shoes the drums will not go past their .060 limit. Also, drums on the same axle should be machined to within .010 of each other or the brakes might pull to one side. That's was what was recommended back when their were licensed brake adjuster shops. A larger rotating drum, as little .010 larger, sounds like no big deal but a larger rotating surface has more leverage, so the force applied to the shoes will be different. You want everything thing as equal on both sides as possible if you want your drum brakes to stop perfectly straight. They are not as forgiving as disc brakes.

"Always" install new brake springs. The break when they get around ten-year's old.

Remember on early Ford shoes the "long" shoe goes towards the front because these are not "self energizing" brakes. Everybody has been taught the long shoe goes on the rear when doing a brake job. That's true on everything except Early Ford brakes.

Arcing brake shoes became illegal, probably in the early 1980s, Shops were inspected by Osha and fined big bucks if they found a shoe arcing machine in your shop. That was because of the airborne asbestos they caused. I went to a Bendix brake class. The instructor said our brakes do not contain any asbestos but that does not mean what's in them is not just as dangerous. When you buy brake shoes they are arced to be used on a drum diameter from standard to .060 over. That is because on a daily driven car the shoes will rapidly wear into the diameter of the drum. The braking will improve as the shoes quickly wears in. On a collector car that's hardly driven this may never happen. That's why its a good idea to arc them. There is not single shop in my town that does this so I went out and bought my own Ammco one for $100.00, That was dirt cheap, I got lucky. on Craigslist.

I was thinking that if you did not have the machine maybe you could use contact cement (Gasgacinch gasket sealer) and stick some sand paper to the drum surface and use this to arc the shoe to the drum. The long strips of sand paper for doing body work would be good. If I remember correctly, the arcing machine uses an 80 grit drum.

[Kube]

Originally Posted by 51woodie

The comments on the amount that can be removed are correct, 12.060". The thing that was not mentioned is the fact the brake shoes need to be "re-arced" to match the drum I.D. after machining. When I was in school taking auto mechanics, any time we did a brake job (all drum brakes at that time) and machined the drums, we would put the shoes on the arcing machine so they would match the respective drum. Old school. I had to "hand fit" my new shoes when I did my '46 last summer. Granted, the shoe itself is supposed to flex a bit when applied, but if arcing is not done, the braking capacity will not be there. If you are in doubt, set up your brakes, take a short drive at slow speed while applying the brake several times. remove the wheels and drums and check for shoe contact.

Like you, I was taught the ONLY way to [properly R&R brakes was to arc the shoes to fit the drum diameter. I've done quite literally hundreds of brake jobs and every one received properly arced shoes.
The performance when arced properly is amazing vs. shoes that were not properly installed.

[Kube]

Originally Posted by 12secvx

I’m aware of arching shoes to fit drums. I guess I’m in the market for a new used set of front and rear 35 drums. Darn it this just got very expensive

Don't fret. Front drums are fairly common and as such, not terribly expensive. Plus, in the short and long term, isn't your safety worth the cost?

[Brian]

good 35 drums., front or rear are not common; they are a one off year, different to 34, different to 36. It's about time someone stepped up and cast some up.

[12secvx]

If someone cast new drums for the 35 Ford and sold them for around $60-$75 each they would sell them. Guys are wanting $80-$100 a drum used with maybe one turn left on them that is why I’m even considering using the drums I have. .100” isn’t paper thin it is over a 1/16” and 35 drums have ribs around the outside that would help support the material that is left. I’m beating my head against the wall on this one honestly. I run 35 wires on my model A and want to keep the drums to help support the wheel.

[Juergen]

This has been discussed many times, especially when someone claims that .060 is the legal limit. When asked to document, no one responds. Ford never spec'd the limit for these cars even though they did for trucks. And I have a GM brake drum that says the limit is .090. So much for never.

[skidmarks]

Originally Posted by 12secvx

If someone cast new drums for the 35 Ford and sold them for around $60-$75 each they would sell them. Guys are wanting $80-$100 a drum used with maybe one turn left on them that is why I’m even considering using the drums I have. .100” isn’t paper thin it is over a 1/16” and 35 drums have ribs around the outside that would help support the material that is left. I’m beating my head against the wall on this one honestly. I run 35 wires on my model A and want to keep the drums to help support the wheel.

What year axles and brakes are on your model A?

Later hydraulic brakes and drums, you can use a support ring with 35 wires.

[12secvx]

I run a stock model A rear axle. And 35 front axle with 32 spindles and spring perches. It has 35 mechanical brakes all around.

[Tinker]

Originally Posted by 12secvx

If someone cast new drums for the 35 Ford and sold them for around $60-$75 each they would sell them. Guys are wanting $80-$100 a drum used with maybe one turn left on them that is why I’m even considering using the drums I have. .100” isn’t paper thin it is over a 1/16” and 35 drums have ribs around the outside that would help support the material that is left. I’m beating my head against the wall on this one honestly. I run 35 wires on my model A and want to keep the drums to help support the wheel.

I'd think if someone did a good wide five drum setup they could get more then a $100 a wheel. People can spend $1000 a "rim". I would not think a solid wide five drum couldn't be sold for a least $200 a hub. $60-80 would be amazing.