Model A brakes

Synchro909

Synchro909

Well-known member
We all know that by today's standards, Henry got it wrong with the brakes on the Model A. He gave the rear brakes too much bias. I have gone a long way to correcting this by putting cast iron drums on the front and fitting those wedges with the floating pins. It's not bad now but another idea has occurred to me and I'd like to know what others think.
The brake actuating arms on the back wheels are longer than the ones on the front. What about putting a set of rear arms on the front? Does anybody see any obvious problems with this, like the shafts are different diameters etc?
Now I'll sleep while you guys mull it over!
 
The physics of your idea is good, that is, the longer brake lever will provide the larger applied braking force. However, I do not remember if you can interchange the front and rear brake arms. Also, the front brakes should engage first because that is where more of the car's mass is situated.

It has been my experience that the largest improvement in braking is had by modifying the brake shoes to find their own centers in the drums, like Chrysler's center plane brakes. Flathead Ted's brake floater kit works very well.
 
"Also, the front brakes should engage first because that is where more of the car's mass is situated."

all "A" brakes are adjusted so that the rear start being applied before the front, having it the other way could start skidding and lose control of steering,
same principal with all bikes, always start braking with rear brake first.
 
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By putting the longer arm on the front (and yes some adapting of the shaft must be done - but easily done) the brake rod that pulls the lever must now travel a longer distance to get the same rotation at the shaft. Now rotation of shaft determines travel of the push rod inside the king pin which in turn, in turn determines travel of the shoes to contact point.

Length of lever at brake crossover rod may also have to be lengthened to get the desired effect you are looking for.

As Bob alluded to in above post the physic can get complicated.

If it were mine I would make sure EVERYTHING was working correctly, my tires could slide on the pavement, then go to floaters and other minor brake adjustments. Tires sliding on the pavement - does not get any better than that. ken
 
Even on modern cars, the rear brakes are applied first. This balances the car, and then the front brakes come on, but a bit harder so the fronts brake harder than the rear. The A is sort of the same, the wedges inside the drums expand the shoes at a different rate, so the rears come on first, balancing the car, then the fronts come on a bit quicker than the rear, but not to be nore than the rear brakes, but returning them close to 50/50. If you look at the rear wedge rod device, the ramp changes rate by not being a constant radial sector. The front wedge ramps also have a visible change in rate when you look at them.
 
Synchro909 said:
We all know that by today's standards, Henry got it wrong with the brakes on the Model A.
Click to expand...


Would you please show me proof of your statements with actual data?

Are you sure that the front and rear systems activate the brakes at the same rate?

I ask because I have found conflicting statements from people on this subject.

I have not located any data to show the rates from the mechanical ramp system between the front and rear are equal. That is what has to be true for the statement that the rears are to take more of the braking action.
It is not clear (verified repeatable data or Ford's detailed prints) at this point that the statement is true.

If the rear wedge moves the shoes at a slower rate per angle of level rotation then you will need the rear drums moving sooner to equalize the application. I have not been able to confirm this.

What we do know is many brakes systems are put together incorrectly. All the pieces need to be put together exactly as what I certain of is the fact that Ford built them to .001" tolerances. A person who frequents the archives looked up some info on brake print (the diameter of the shoes) and was shocked to find many prints covering the operation of the brakes with .001" of accuracy in the movement of the shoes.

So with so many brakes put together incorrect, it is tough to make any proper conclusions. We do know those who take great pains to make the system like it came from the factory report excellent brakes.

So anyone going to Benson archives want to take some time to look up the brake prints and see if there is any info on the application rates of the brake wedges for angle of lever rotation?

Until then all we have is people talking and no proof. It is all just wind.
 
Totally agree with you Kevin about " where's the proof of the data"... and furthermore if the brake system was put together with a tolerance of just .001" I wonder how long it lasted at that accuracy ...A week of normal motoring perhaps?
 
Here are instructions on how to adjust Model A brakes...

To insure correct equalization have 1 man only check the brake pressure by rotating the wheel. If the above adjustments are correctly made the brakes should operate as follows:
1- Rear brakes should just start to hold when brake pedal is depressed approximately 1 inch.
2- Depressing pedal about 1 \2 inch farther should tighten but not lock rear brakes and cause front brakes to just start to hold.
3- Depressing pedal approximately another 1\2 inch should lock rear wheels and hold the fronts very tightly. With properly adjusted brakes they should not exceed 1\2 of the total possible pedal movement.
4- When brake pedal is applied with full pressure, rear wheels should slide and fronts should make a heavy impression or road print, which condition is obtained just before sliding.

It is obvious from these instructions that when adjusted properly, the rears come on first and continue to outperform the fronts through full brake pedal travel. Also, on a Model A, the front and rear brake shoes and drums are the same size.

On a "modern" car, most of the braking is done by the front brakes...75% in most cases...the opposite of our Model A's. This is done by a combination of smaller brakes in the rear and lower hydraulic pressure to the rear brakes. Rear brakes do come on first on modern cars like our Model A's, but only for an instant. Then the majority of the braking is taken over by the fronts.


There are plenty of articles on the web describing modern brakes. Google "brake proportioning" or "front vs rear brakes". Here's one for starters...


http://knowhow.napaonline.com/front-brakes-vs-rear-brakes-whats-the-difference/

Ted's Kit is brings the braking of our A's closer to the physics of a modern car (at least in terms of front vs rear braking) by allowing the shoes to float and self energize. Here's an article explaining how it works...

http://www.ocmafc.com/techarticles/BrakeFloaters.pdf

Again, plenty more info on the web about Flathead Ted's Kit. Google "Flathead Ted".
 
If you want to try longer front arms use some from an 30-34 AA or BB.

Bob
 

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Dick Steinkamp said:
Here are instructions on how to adjust Model A brakes...


It is obvious from these instructions that when adjusted properly, the rears come on first and continue to outperform the fronts through full brake pedal travel. Also, on a Model A, the front and rear brake shoes and drums are the same size.



Ted's Kit is brings the braking of our A's closer to the physics of a modern car (at least in terms of front vs rear braking) by allowing the shoes to float and self energize. Here's an article explaining how it works...
Click to expand...


Please explain how the instructions show that the rear brake are providing more force of braking to the rear wheels?

What if the rear wedge expanded at 20% less rate then the front wedge? What if you were to start the rear sooner so it would be braking at the rate needed for the 60/40 split to the front?

I do not know if that is true or not. You are telling me it is true, how do you know? Please show me the evidence. Until then you are just second guessing some pretty smart engineers that Ford paid to design the brake system.

I am looking at this from the view of a scientist. I have NOT found evidence to prove either side. So until then I build them like the factory built them. We know that works great.

As for Flathead Ted and his system.

Ford did eventually move to a similar system with the late 36 Ford brakes. I have not used his system, but when Brent Terry says they have issues and he will not install them- well I give some weight to what he says. He seems to find a full correct rebuild back to factory specs works best. He stands to loose a lot in litigation if brakes do not work.
 
If there is more weight in the rear and the wheels lock up first, is there not more braking force in the rear?

Older people still to this day can have problems riding a bicycle because they were taught that the front brake makes you go over the handle bars!

If you modify a brake system for a paying customer, then end up in court, what could happen?
 
Bob's post (No 9) shows that Ford themselves went the way I was thinking about and the instructions in Post 8 confirm that there is too much braking on the rear wheels of a standard Model A. Like I said though in my first post, I have achieved a good balance by other means, a balance I have absolutely no intention of changing. I have driven about 50,000 miles with the setup I have. This thread is just throwing another idea out there.
 
Syncro yeah we wouldn't have all the innovations in autos if nobody tweeked things to attempt improvements, think hotrods and race cars. Kinda like NASA bringing us miracles from space.

My brakes are set up as factory with the exception of cast iron brakes. I get a skid if my leg chooses one!
 
My $.02

A few years ago I set up my brakes (1931 ccpu) according to the process in "Model A Mechanic's Handbook". Shortly thereafter I had the need to make a panic stop and found that all 4 wheels locked up from about 30mph or so. A short time after that I had to do it again (what was I thinking?) and the same thing happened.

The lesson? If the brakes are properly set up and adjusted, they do the job quite adequately without the need for after-market add-on doodads.

Just sayin'...
 
I think that originally Model A were set up with rear break bias because roads were largely dirt. If I was driving mostly on dirt I would set them up that way. However I drive mostly on paved roads so I have the bias in front. Works for me and I'm not about to change it.
 
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