VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 33 turning drums

I would like to know what the minimum thickness for the brake drums on a 33 master is. I have one of the fronts on and ready to start machining. Is it even OK to turn the pressed steel rims?
Thanks Don

[img:center][/img]
Just thought some of you might find my antique lathe interesting. This is where I'll turn my Brake Drums. This lathe actually came from a shop that used it for just that purpose.
Don

I have a South Bend 13" I use for brake drums and flywheels also...I also use thee slowest speed and very fine feed , high speed steel tool w/virtually no radius. Takes awhile but finish is excellent . Kevin

Hi Don,

Don't know about a 33, but on Chev 4's it is not advisable to turn pressed drums.They are allready thin and reducing the thickness will generate more heat and reduce your braking effect. Other readers may have more experience with 33 drums. With mine I mounted them on a bench grinder and just cleaned up the surface with a pad mounted piece of emery paper.I would suggest replacement rather than machining.

Cheers

Ray

I have a '34 with pressed drums also. I vaguely recall being told that steel drums were ground and not turned, yet I've never seen a place that does it. Seems to me if they're too thin to turn, then they'd be too thin to grind as well. How much of that is legend?

My 1935 Kent-Moore Tool Manual shows a brake drum lathe KMO-114
The advertising claims it can machine Chevrolet, Pontiac, Buick, and Cadillac drums, and truck drums to 24-1/2 inches in diameter. What is interesting is the drum is held in place and the cutting tool revolves around the drum. (eliminating chatter) Could also machine drums with axle mounted-four standard sized passenger drums in 35 minutes. How many dealers had these machines is anybody's guess. Base price was @ 350.00

The steel drums should be ground and not turned. However, I did have my 1930 brake drums turned on a lathe by a fellow that knew how to do it correctly and they came out great! Can't take much off though because the steel drums are too thin. And, if the steel drums have been turned before then you shouldn't turn them a second time.

I would agree on the grinding. Years ago I also had a pair cut on a lathe by a pro and never had any problems, but would rather grind. Don't know if a machine is available to grind the rears with the axle attached though.

Talking about drums getting too thin to turn.

What they did in Greece years ago when labor was not so expensive:
On drums that were hard to find or expensive to replace they buildup the inner diameter of the drum with a layer of metal (with the correct electrodes ) and then turn them to the required diameter.
Was this method ever used in the United states?

Jianis

JianisNl, In the rebuilding of aircraft engines they have a process where they "chrome" the insides of the cylinders to build them up to original size. After the chroming process they are bored to the proper size. I had also wondered if the same process could be used on brake drums. I'll have to look in to who might be able to answer the question.
Don

Hi Don,

There is a guy in OZ who rebuilds drums for Chev 4's by cutting of the face from the cylinder on a lathe, welds on a bit of continuous piping with no seam, and machines back to true. But thats only on the rears that dont have the return lip as the fronts do.

Cheers

Ray

I'm beginning to understand why many don't bother restoring 33 Chevrolets.
Don

Ah Don,

But think of the fun your having, not to mention the challenge.

Also in a year or so when you are motoring down the road with the wind in your hair, presuming you will still have hair by then from the stress, you will say

"These are the good days"

Cheers

Ray

The issues are pretty much the same with any old car that is restored.

I like the idea of adding metal and then machining as I have a '36 standard with a couple drums that are not quite round. I have found some NOS rear drums but no fronts as of yet.

You know me as if you were my brother.

I've had an interesting replay on the hard chrome process. I'll continue to look into this.
Don

I'm sure it's expensive.

Don

I am an aircraft mechanic so I am aware of the hard chroming process. Thats expensive work, Here in Europe the same process is used on 2stroke motorcycle cylinders but thats only a minute thickens car drums should need lots more!!

Jianis

Getting the bore of the drums hard chrome plated wouldn't be any good,as the chrome would be too "slippery",and the co-efficient of friction between the brake lining and the chrome,would be entirely different to the original pressed steel.You'd probably have a good hard brake pedal,but would have to push so hard on the pedal to try and pull the car up.
If you could find a brake lining compataible with a hard chromed lining face,then the chroming may be the way to go.
Going by the picture of the drum in your brake drum lathe,it appears to have a "stiffening" lip around the edge?If it does,another possible alternative would be to have the drum bores metal sprayed,then you could machine them back to standard size.Again you'd have to find a metal spraying powder that would be compatible with the old type of linings used on mechanical brakes to gain the friction between the linings and the drums.
Failing that,you could try as 1928 is Great said,machine the old piece of the drum off leaving the axle flange face,get a piece of seamless thickwall steam or hyraulic mild steel pipe cut to the right width(with a little extra for final machining)
fully weld it,inside and out,then machine the bore and outside diameters back to standard.It would be best to turn the outside of the drum first,then wrap some rubber strip arond the outside(up to at least 1/4" thick),then bore out the inside of the drum.The rubber will tend to stop the steel drum from "singing" as you machine the bore out to its proper size,and the wall thickness is reduced back to standard.

CJP

You are right.
I forgot to mention in my last post that hard chrome is used in the cylinders to reduce friction between the piston rings and the cylinder walls so it should not be any good for braking.

Don
By the way I thought my lathe was old but yours is even older

Jianis

Don ... I'm sorry we got so far off your original question : What is the "Maximum ( Inside ) Drum Diameter Size"? Of course more modern drums have it printed on the side but...maybe we can find it written some where's...

Depending on the model,here is some brake drum bore dimensions I found:

1933 CA Master Front & Rear 12" internal bore(new drum)

1933 CC Standard Front & Rear 10" internal bore(new drum)

Lining width front & rear Master CA 1 3/4",thickness 3/16"
Lining length(total per wheel)front & Rear Master CA 35 11/16"
Lining width front & rear Standard CC 1 1/2",3/16" thick
Lining length(total per wheel)30 1/2"

Hope information is of some help.

This has been great information. I'm sure others must have similar questions. If possible keep the ideas coming.

Thanks CJP...At least we have a starting point . Now if Don can check what he's got on his drums...I would imagine you can go .125-.150 over the new dia. (max.) or less if it'll clean-up...

With pressed mild steel drums,you can't afford to remove very much out of the bore,or the drums become too thin and springy,and the pedal will feel "spongy" when you apply the brakes.
The drums would possibly have about 3/16" wall thickness when new,and a 0.005" - 0.010" cut would probably all I'd take when machining.
The Bendix brake book I have gives limits for drum thickness when machining/grinding,depending on the drum size,and for example on my '27 & '29 Olds,the minimum drum wall thickness when machined from an original wall thickness of 3/16"(0.1875"),is 0.137",making the bore larger by 0.050" on the cut radius,and the overall drum bore increasing by 0.100".
If the drums are machined o/size,you can run into problems getting the right thickness of brake lining,or you either have to place special packing shims between the shoes & lining to compensate for the larger bore,or go for thicker linings,and have them radius ground so the lining conforms to the drum bore perfectly.