Brake drum ouch

3

37slantback

Senior Member
Hi,

I had a local shop turn my 37 wheel drums. I guess I didn't make it absolutely clear that if any drum needed more than .060 , stop and call me. I don't blame the guy. In his mind this is the way they used to do it and you just use oversized shoes.

I want to confirm my belief that a .120 turn has made these drums useless. ( dangerous)
 
37slantback said:
Hi,

I had a local shop turn my 37 wheel drums. I guess I didn't make it absolutely clear that if any drum needed more than .060 , stop and call me. I don't blame the guy. In his mind this is the way they used to do it and you just use oversized shoes.

I want to confirm my belief that a .120 turn has made these drums useless. ( dangerous)
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Most/all drums have an oversize number cast into the hat or rim, and is usually the standard .060" oversize. Any shop turning drums (or rotors) should know, or learn, the maximum oversize dimensions before machining, or they should not be doing brake work! Could be the machinist thought .060" was the actual maximum feed cut spec, which would result in a .120" oversize. More reason to find another shop!

I'm not familiar with mechanical brake drums and their specs, but if the design oversize was .060" over, your drums are now "useless and dangerous". The shop could be liable for part or all the cost of new or useable drums.
 
Guy must have been a newby. Even when I was a kid, I understood the value of only removing the amount necessary to clean things up. A friend of mine did most of the drum turning and he would stop at .060 even if there was some shallow grooving left. He would then ask the owner if he wanted to go a little farther at his own risk. Even then he would never go much more than .020 over max depending on the manufacturer of the drum. A little grooving left will usually still allow for normal brake function.

Kerby
 
He came recommended by a guy in the EV8 club and apparently has been doing it for 30 -40 years. In the "old" days, he said they would hog them out and user oversized shoes. Again, always an education.
 
V8 Bob said:
Most/all drums have an oversize number cast into the hat or rim, and is usually the standard .060" oversize. Any shop turning drums (or rotors) should know, or learn, the maximum oversize dimensions before machining, or they should not be doing brake work! Could be the machinist thought .060" was the actual maximum feed cut spec, which would result in a .120" oversize. More reason to find another shop!

I'm not familiar with mechanical brake drums and their specs, but if the design oversize was .060" over, your drums are now "useless and dangerous". The shop could be liable for part or all the cost of new or useable drums.
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I must have led a sheltered life. I have never seen an oversize number cast into an old Ford drum (pre '48) except for the new reproductions that have been designed to turn .090 and are so marked.

I don't think the shop should be liable for the cost of the drums assuming they had to be turned .120 to clean up (and they didn't make any mistakes). I do think they should pay the cost of turning since they created scrap with their work. Check to see the state law and if it is .060 point that out to them.

Charlie Stephens
 
I tried to get some 36 drums turned when I went back he hadn't done them ,said he was not allowed due to the law ,as they would be over the max allowed .If your guy has been doing them for 40 years in practise he may know the limits.If you are just running around town as a tempery measure maybe they can be used if you are on rod brakes ,.The outer rim can crack away from the inner but you would get a warning noise and unlikely loose all four .The other problem is getting the linings thick enough ,
 
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I had worked at various Ford dealers for many years and any shop manual ( even up to 2011 ) state that .60 is the max to turn a drum or rotor. Now they actually list a minimum diameter size you can go to. With the minimum amount of material they make rotors or drums, 99% of the time they're junk when it's brake job time. If you have a 11 inch drum, then, 11.60 is the max.

Barry

50 F-1
 
Charlie Stephens said:
I must have led a sheltered life. I have never seen an oversize number cast into an old Ford drum (pre '48) except for the new reproductions that have been designed to turn .090 and are so marked.

I don't think the shop should be liable for the cost of the drums assuming they had to be turned .120 to clean up (and they didn't make any mistakes). I do think they should pay the cost of turning since they created scrap with their work. Check to see the state law and if it is .060 point that out to them.

Charlie Stephens
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Charlie, I don't when they started to cast in the max ID dimention in drums, but .060" has been a default standard for as long as I can remember. The shop HAS to know the actual max ID for the drum they are machining, and stop at that point, clean or not, as it's now up to the owner to use it, or not. Drums (and rotors) don't have to be perfectly clean to be usuable, but when they are well over the design ID, they can fail, and are not worth the risk. Add the fact they are over 70 years old, if it was an original!
 
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One of the problems of turning a drum too large a diameter is that there's much less material left in the drum to "soak up" the heat generated when stopping. Get going 40+mph, jam on the brakes and they'll get VERY hot. As they heat up, they expand resulting in greater shoe travel to stay in contact (brake fade.) Are you only going to be loading and unloading the car from a trailer? Or, maybe piddling around town at 15-20mph? If so, you may be fine. Take it out on a highway and keep up with the traffic? Fugget about it!!
 
Is anyone aware of new drums for 36-39 Fords? I specifically haven't had the drums on my 37 turned because of this problem.
 
Barney with the red light on top said, if you want to keep your inspection licence you can turn drums to only .060" over and must junk them when they wear to .090" over unless they are stamped otherwise.
 
ANY guy in the bussiness has a drum mic... And enough experience to tell what he can turn out in the way of a job on a brake drum, (Been there) and the difference between radius and diameter. For myself, I would look at the .120 over and see what the remaining thickness is- and IF I lived on a big hill, take that into account... Cast iron BREAKS, it does not bend, so if you feel anything, it's too late to take warning...
IMHO... Karl
 
If you are running .120" over drums and you run over someone. Then the investigation finds oversize drums were the cause. Is it worth it, you make the call. Bubba just found a new *****.
 
I'm going to offer a little 'conflicting' opinion, here.... And, I'm well aware of the current thoughts about .060-over as max, etc, etc. In my view, the previously posted thoughts are 'right-on', and reflect a conservative, safe approach.
However, in my 'old-days', meaning back in the 50's when I worked in a few independent shops, we routinely saw brakes that were more than .060 over, and fairly often .120-over. I'm not saying that I recommend this. I AM saying this has happened, and I never saw failures, and the shops that I worked for never had any 'come-backs', or complaints, that I am aware of.
My suggestions, for your case.... Do some measurements yourself, and determine what percentage of the original metal has been removed in the 'critical' areas. Think, and decide for yourself if you feel this is significant.
In-any-event, to get back on the road, put it back together. Then, do what I would call a 'proof-test' (as we would call it in the industry I worked in). That is, sitting still on your own property (or wherever the car is), stand on the brakes VERY hard, and see if you can break anything, or feel any 'flexing'. I'm thinking of a brake-pedal force of 1.5-to-2 times the force you might ever produce in your worst-imaginable panic stop. Assuming this 'passes', then do another test, in a safe, road condition. Get the car up to speed, maybe 35-40 mph (or more), and do the strongest panic stops that you can. This would be 'short' of skidding the tires - I'm suggesting the strongest stop you can do WITHOUT skidding. Repeat at least twice (total 3 times). If you have a 'down-hill' to do this test on, so much the better.
Then, re-think, or re-evaluate whether or not you feel comfortable with your brakes.
If the drums are marginal, or flexing, you might be able to feel 'pulsing' after this test, indicating that you may have distorted a 'weak' drum. (Better to find out this way, as opposed to a REAL panic situation.) And, be advised, with the mechanical brakes on my own early Ford, after three of these 'panic-stops', the brakes will be in the 'fade' condition - ie, hot!
Finally, keep your eyes peeled for drums that are closer to standard... I am aware of TWO recent cases of friends that GAVE-away sets of these style drums, because they were changing to the 5-on-5-5 style, and they couldn't find anyone willing to pay for the old, take-off parts. Find a 'rodder', or rod-shop.
 
Something that I've seen done to compensate for an over-oversized (like the .090" or .120") drum since no one arcs shoes anymore(most brake lathes used to have a shoe arcing attachment) and under-lining shims are very scarce: Hold the new shoe in position in the drum and note how much it 'rocks'. There should be a little clearance at each end of the shoe and solid contact in the middle. When applied, the shoe springs a little and makes full contact. Old shop manuals give the specs. If the shoe rocks too much, hold it on a piece of wood with the lining facing up and smack the middle of the shoe with a rubber or wooden mallet, Check fit in the drum and repeat as necessary. This really works but I can't tell you how I know!
 
I want to thank all of you who have responded. I have a guy that can re-arc some shoes. The bigger story is I needed to get the car where I can drive it to a couple of shops to get some estimates for some other work. I actually have another chassis that this body will be put on. That chassis has updated suspension, etc. My wife has plans for the old 37 chassis so that buys me some time to dig up some drums.

The upshot is slow and easy wins the race.
 
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