Brake Drums - Advice Regarding Their Use

Bob Bidonde

Bob Bidonde

Well-known member
Making your service and emergency brake systems 100% operational and effective is an absolute must do because your life, the life of passengers and the survival of your Model "A" depends on them!


Before cast iron reproduction drums became available, it was necessary to drive with used drums that were significantly grooved, worn thin from wear and turning, and also tended to be out-of-round. For 50 years I bought used brake drums that had serviceable thicknesses, but I accepted grooves in the braking surfaces.


My finding was that grooves did not affect braking because the brake linings soon became grooved to match which increased their braking surface areas. I never had a drum turned to remove grooves. Out-of-round drums I cured with press-fit external brake bands.


I conclude by saying that a used original pressed steel brake drum should not be turned / cut to true its braking surface. If you consider cutting original drums is a must do, I urge you instead to replace them with new cast iron drums. Replace the front drums first if money is an issue.
 
Bob,

With a stock Ford rear brake bias and on a budget, wouldn't new cast iron rears be more beneficial ?

Just asking, jb
 
Front bias will give you shorter stopping distance. If you must only buy two new drums, my advice is to put them on the front and bias to the front. If you use the stamped drums, make sure they are not worn or turned too thin. I think the limit is 0.120 inch. And do not ride the brakes down a grade.

Bob, I agree with you regarding the grooves. In fact I do the same thing with the disks for modern disk brakes. If they are grooved, but not worn too thin, I will use them without having them turned. If too thin I replace them.
 
Thank you for your post, Bob. I'd like to add the following from the Service Bulletins:

As per 1929 Ford Service Bulletins, page 332, Ford implemented a procedure to exchange several critical parts, such as any steel brake drums, which were in need of resurfacing. Ford did not state why the exchange procedure was begun; however, removing material from a steel drum would degrade braking performance further and possibly violate state laws.

As per 1931 Ford Service Bulletins, page 514], under the heading of IMPORTANT, Ford states: “Under no circumstances should Ford steel brake drums be turned down, as they have a special rolled braking surface, and this surface must not be touched with any kind of machine tool.”
 
IMO, Bob is correct about the grooves, nkaminar is correct about replacing the front drums and Rob is correct about never machining steel drums. Bob gives the answer on what to do if they are out of round.
I have never had to cut more than about 0.008" - 0.010" to true up cast drums when I have fitted them and never had one go out of round during use.
If we look at all of the posts ever on here, the number dealing with getting or keeping your car running well or even better than original waaaay out number those dealing with better brakes. I don't excuse myself from that but at least I make sure the brakes are as good as can be. IMO, not enough do.
 
Rob Doe said:
Thank you for your post, Bob. I'd like to add the following from the Service Bulletins:

As per 1931 Ford Service Bulletins, page 514], under the heading of IMPORTANT, Ford states: “Under no circumstances should Ford steel brake drums be turned down, as they have a special rolled braking surface, and this surface must not be touched with any kind of machine tool.”
Click to expand...

Do they roll the surface to create a structure similar to what you get using cold rolled steel (CRS) from the mill? I know machining CRS will release its built up stress from the rolling operation and cause it to change shape. Are they concerned that the drum would go out of concentricity once machined?
 
OK, after quoting miscellaneous unrelated chapters & verses from the Service Bulletins, still no real reason why front drums vs rear drums.

Henry had 15 years of rear brake experience before the Model A and it was for a world mostly covered in dirt roads. This to me explains his rear drum braking bias. Rears drag & fronts guide.

Today with heavier cars cruising faster on solid pavement, rolling on wider tires, front biased brakes are necessary to control 'weight transfer'.

As the Model A has none of that, cast iron drums on the rear still seems optimal.
 
jb-ob said:
OK, after quoting miscellaneous unrelated chapters & verses from the Service Bulletins, still no real reason why front drums vs rear drums.

Henry had 15 years of rear brake experience before the Model A and it was for a world mostly covered in dirt roads. This to me explains his rear drum braking bias. Rears drag & fronts guide.

Today with heavier cars cruising faster on solid pavement, rolling on wider tires, front biased brakes are necessary to control 'weight transfer'.

As the Model A has none of that, cast iron drums on the rear still seems optimal.
Click to expand...


Do your self a favour and run a little test:
- take a little model car, like a scalextric
- take some tape and bock one axle so it does not turn but the other axle turns freely
- let this car run down a slide, first with the rear axle in the back, then the blocked ale in the front
- what you will see is that with the blocked axle in the rear, the car goes sideways and is out of control. Blocked axle in the front, the car goes straight on.


Getting the front axle to block first is what's called 'sichere Blockierreihenfolge', 'safe blocking order' in modern automotive design. And it's just physics, so it applies to Model As too.
 
Now we are getting closer.

The flaw of the slide experiment is the vehicle is accelerating as it descends.

Rather the question is which would decrease speed faster, cast iron front or rear drums on a stock Model A as built??
 
jb-ob said:
Now we are getting closer.

The flaw of the slide experiment is the vehicle is accelerating as it descends.
Click to expand...


I don't agree, the slide does not change the behaviour. Try it with your emergency brake. Go to a gravel road, accelerate and bring your rear axle to block with the emergency brake. Try to keep control of the car...


Rather the question is which would decrease speed faster, cast iron front or rear drums on a stock Model A as built??
Click to expand...
My experience: I live in a hilly part of germany, when i got my car i had huge problems with brake-fade. Both axles were equipped with the thin brake drums. I swapped the front against cast-iron drums and the fade went away. Months later i swapped the rear axle drums against cast-iron ones but did not notice a change.


My vote goes to equipping the front axle with cast-iron drums first.
 
veggie said:
TOM I think i miss spelled BLOCKLLERRENRRFOLLGE .Thats what makes the leaves fall in the Fall.
AL
Click to expand...


You wanna play Hangman with a german?

Blockierreihenfolgenregler

Blockierreihenfolgenreglereinstellung

Blockierreihenfolgenreglereinstellungsbeauftragter

Blockierreihenfolgenregler-
einstellungsbeauftragtersicherheitsausweis
 
Tom,

If I attempt to stop my car with the emergency brake, the car stops straight while destroying the E brake carrier.

Ultra high speed race cars at Bonneville use drag chutes to stop, always deployed from the rear.

In my lethargic Model A, I'll keep the 'anchors' in the rear. Thanks for your thoughts.
 
jb-ob said:
Tom,

If I attempt to stop my car with the emergency brake, the car stops straight while destroying the E brake carrier.

Ultra high speed race cars at Bonneville use drag chutes to stop, always deployed from the rear.

In my lethargic Model A, I'll keep the 'anchors' in the rear. Thanks for your thoughts.
Click to expand...


And it will be fine as we are not going 'a mile a minute' in our cars. At least i am not. But i am also a physicist, so i have to make my comments and remarks. Sorry about that.
 
Sorry veggie, not surprisingly you missed question as not a contest.

I suspect both Tom and the original poster ( I respect), would dismiss anecdotal evidence as insufficient to draw an intelligent conclusion.

Your mileage will probably vary.
 
"Henry had 15 years of rear brake experience before the Model A and it was for a world mostly covered in dirt roads. This to me explains his rear drum braking bias. Rears drag & fronts guide."

The Model T had the worse brakes in the automotive history. They were in the transmission, bathed in oil, and had cotton bands run on CAST IRON drums. The rear wheels had formed steel drums with cast iron shoes, no friction material. This was a parking brake and useless for slowing down the car. In fact they did not even work for parking. You will see drivers of Model T's carry blocks to put under the wheels to keep the car from rolling on the slightest of slopes.

Locking the brakes will decrease the stopping distance, rear or front or all 4. The ideal situation is to have all 4 wheels just on the verge of skidding. The brake on modern cars does this with the aid of a computer. If you bias the brakes to the rear the rear wheels will skid way before the front. Biasing to the front will put more braking on the front where the "weight transfer" has put more downward force on the pavement. And it will keep the rears from skidding until more force is put on the brake peddle.

In stopping tests I have done with my 1930 Fordor, the stopping distance at 20 mph went from 22 feet to 17 feet with the bias in the front. The rear brakes still left a black mark on the asphalt. This is a 29% improvement in stopping distance. And I can tell the difference in normal driving too. There is no tendency to spin 180 degrees.
 
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Following what another member of this forum did, I bought two rear brake arms and replaced the two fronts on my Coupe with the taller rears. I haven't tried to see how much better they are with a bunch of panic stops on rain slick fresh asphalt, but just ordinary everyday driving I have to admit the brakes do a better job of stopping the car and the few times I have hit them rather hard, the car slowed in a straight line, unlike the thrill that used to produce. so I'm inclined to think the stronger stopping power to the front is a good thing on my Coupe. Your results may vary. Not for Shw cars.
 
Davey, On a '31 Fordor recently for sale it appeared that a previous owner used early (AR) front activating arms (taller) with the double clevis on the brake rods, no doubt hoping for an improvement.

Four wheel brakes on asphalt are a vast improvement ( lease a new Lexus) over what Henry created for his world.

Very long a go it was drilled into my head never weld suspension pieces or hamster with brakes. Concept still hard to shake.
 
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