Mechanical brakes, what i did

When I started working on my model A and read how the brakes were set up with more braking on the rear I was of the understanding that they did this so under normal braking you would not lose steering control while braking. With that in mind, I think that was some of the reason for ABS brakes in modern systems. Just a thought.
 
James Rogers said:
So, let me get this straight. You lengthened the front levers to get more force and leverage to the front brakes but shortened the steering (pitman) arm to get more force and leverage to the steering? Seems like a contradiction here.
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Not really, because the pitman arm APPLIES the force, and the brake shaft arm RECIEVES the force.

I understand the idea of the longer brake arm multiplying the force, but with the shorter brake arm movement, the brakes would need to be kept in closer adjustment; ie, if the brake shoe wear is allowed to accumulate before readjusting, it seems any leverage advantage would soon be lost. I haven't taken much time to think this modified brake arm theory through because I'm satisfied with my stock brakes.

If you want more braking from the front brakes, then it seems installing floaters on the fronts ONLY would be an easier way to go, and it would be easily reversible if it didn't work to your satisfaction.
 
I started to write this yesterday morning but was pulled away. Since then some have thought through the concept.

What Chris did was increase the leverage to the fronts which were technically under leveraged compared to later cars when Ford finally understood the reality of front versus rear needs. Yes, this does slow the actuation of the front brakes. That is normal and unavoidable. Look at the ratios of any block and tackle. The lift capacity is not determined by the size of the cable or rope (although it must be suitably sized), but the the capacity is determined by the ratio or number of wraps of the cable. The more wraps, the slower it lifts but the more it lifts with the same applied force.

Everyone assumes the Model A front brakes actuate or engage at the same rate as the rears. This is not the case. The topic came up about ten years ago regarding an article written suggesting the brakes could be adjusted 50-50 or 60-40 front-rear. I explained at that time it was simply a fallacy. In doing so you are simply reducing the function of the rear brakes and FORCING the much stiffer (less leverage) front brakes to do more of the work. Think of it this way, shortening the front brake rods to make the front brakes come on earlier is the same as lengthening the rear rods to come on later (reducing rear brake function) except the latter lowers the functional height of the brake pedal. I further explained that to even equalize the braking force at the drum (front to rear) you must actually equalize the leverage. This essentially also means making the brakes actuate at the same rate.

Now it's important to note that the simpler linkage of the rear brakes DOES provide a slight mechanical advantage due to efficiency but not nearly to the extent that the the added leverage (and slower actuation) does. Adding leverage to the fronts will similarly slow the actuation which can then be adjusted to engage at the proper time. Wear will not cause any future adjustment issues assuming the modification is not too extreme.
 
Like Marco, I have been composing a reply in my mind; in my case, from my perspective as a professional restorer of vintage brake parts. Marco's comments are as usual excellent and on the money, so I won't try to duplicate them.

The only downside to this change is the slight increase in pedal travel, but it is IMO insignificant compared to the increased braking response and the improvement in braking bias. As Marco mentions, even Ford soon realized he had the ratio wrong. It's much safer for the fronts to lock up first than the rears.

Sure would be nice to see these arms show up in the repop market with the short pitman arms.

Joe
 
somethings wrong here ? see if i got this worng !
at least more than a few (hundred) discussions here over the years. have most concluding/procliaming....Ford got it right, leave it alone stock with mechanicals...yada,etc!
now..'experts' are claiming ford got it wrong and that he realized it! then some A owner comes along with a homebrew mod and its proclaimed that that mod should be offered on the market for general consumption, to 'improve' (correct) fords mistake....'for improved' mechanical brake use. look out floaters...hereyecom!
Q... if improving model A brakes is truly the goal, why not just do the hydraulic bendix system? even ford knew that hydraulics system was the best..and eventually went with that ? yikes...would/could this be considered (gulp)rodding? no pun intended!
 
hardtimes said:
somethings wrong here ? See if i got this worng !
At least more than a few (hundred) discussions here over the years. Have most concluding/procliaming....ford got it right, leave it alone stock with mechanicals...yada,etc!
Now..'experts' are claiming ford got it wrong and that he realized it! Then some a owner comes along with a homebrew mod and its proclaimed that that mod should be offered on the market for general consumption, to 'improve' (correct) fords mistake....'for improved' mechanical brake use. Look out floaters...hereyecom!
Q... If improving model a brakes is truly the goal, why not just do the hydraulic bendix system? Even ford knew that hydraulics system was the best..and eventually went with that ? Yikes...would/could this be considered (gulp)rodding? No pun intended!
Click to expand...
Exactly!
 
Tibor said:
I understand what your saying im only an enigneering student but I did make it to staticts, dynamics, and physics. You are saying is that by lengthing the front brake arms you trade force for distance. Simple mechanics, Like using a pully set up. You have a longer arm so you have more torque but you have to increase the distance in pedal throw.
just out of curiosity what feild of engineering were you in?
Tibor
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You have the picture, Actually, it is a very simple basic concept.

I am a Mechanical Engineer and have worked in the automotive field for about 50 years.

Good luck with your schooling. I found Mechanical Engineering to be a very interesting field, especially if you are into cars.

Chris
 
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James Rogers said:
So, let me get this straight. You lengthened the front levers to get more force and leverage to the front brakes but shortened the steering (pitman) arm to get more force and leverage to the steering? Seems like a contradiction here.
Click to expand...

Steering is the opposite case of brakes. With steering, it takes a fixed amount of force (push or pull) on the drag link to turn the front wheels. To DECREASE the torque of the pitman arm (which is directly related to steering effort) required to produce that fixed amount of force at the end of the steering arm, you SHORTEN the length of the steering arm. Force x Length = Torque. For a given force, as the length decreases, the torque decreases.

With brakes, if you want to INCREASE the torque of the operating shaft without increasing the pulling force on the end of the lever, you INCREASE the length of the lever. Force x Length = Torque. For a given force, as you increase the length of the lever, you increase the torque. Increasing the torque of the operating shaft will increase the braking effort (apply the brakes harder).

It is all mechanics.

Chris
 
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A non-mechanical mod to shift braking to the front is to use woven linings in the front only, harder molded in the rear. Worked for me.
 
Ford went from Model T Brakes, (Rear brakes only) to Four wheel Brakes with the Model A and a 40/60 Front to Rear Bias. This was a BIG STEP. From 32-38, I am not sure if Ford maintained a 40/60 Bias but I suspect they started to shift to more front bias. By 1939 the went to Hydraulics which had a design bias of closer to 60/40. I believe by 1946, they even increased the size of the front wheel cylinders and were probably closer to 65/35.

In 1928, I do not think Ford had a real good understanding of brake bias (no body did) and they felt they did not want to lock up the fronts so as not to loose steering. In actuality, locking up the rears well before the fronts can cause the vehicle to "swap Ends". Have you ever driven an old Pick-up with no load in the rear on a wet winding road and have it turn around on you for what you thought was no reason. The rear brakes locked with light applicatiion and you lost all control.

All I have done, is used a little more modern thinking to improve the operation of the Model A Ford Brakes. This is a VERY simple modification and it really works well. I have another Model A with original brakes in good working order to compair it to.

I guess this is sort of like the shortened steering arms, some of us enjoy easier steering.

Again, This is what I did and I am not suggesting others do the same.

Chris
 
CWPASADENA said:
You have the picture, Actually, it is a very simple basic concept.

I am a Mechanical Engineer and have worked in the automotive field for about 50 years.

Good luck with your schooling. I found Mechanical Engineering to be a very interesting field, especially if you are into cars.

Chris
Click to expand...


But remeber engineers arn't allowed to no anything about cars especially about fixing them. Just ask someone from the general public and they will tell you.;)

I like what you did, Im going to consider doing this modification to my A. Thanks for the luck ill take all i can get.
 
I don't get it? I put my foot on the brake pedal and the cars slows to a stop. I slam on the brakes all four wheels lock up. No spinning around, no sideways sliding.

I guess this whole thread to me falls under it's your car do to it what you want.
 
hardtimes said:
somethings wrong here ? see if i got this worng !
at least more than a few (hundred) discussions here over the years. have most concluding/procliaming....Ford got it right, leave it alone stock with mechanicals...yada,etc!
now..'experts' are claiming ford got it wrong and that he realized it! then some A owner comes along with a homebrew mod and its proclaimed that that mod should be offered on the market for general consumption, to 'improve' (correct) fords mistake....'for improved' mechanical brake use. look out floaters...hereyecom!
Q... if improving model A brakes is truly the goal, why not just do the hydraulic bendix system? even ford knew that hydraulics system was the best..and eventually went with that ? yikes...would/could this be considered (gulp)rodding? no pun intended!
Click to expand...

I am NOT saying "Ford got it wrong". I am saying "Ford did the best they could with the knowledge they had at the time".

Hopefully, the understanding of brake dynamics has increased in the past 80 years. Adding more front bias definately will improve the overall performance of the braking system.

NOW;

This is NOT some "Homebrew Mod".

This is a well engineered, well designed and well executed modification.

I WAS NOT GOING TO GET INTO THIS BUT:

MY BACKGROUND IS:

I am a Degreed Mechanical Engineer.

I have worked in some facet of the Automotive Industry for more then 50 years.

For many years, I was in charge of the Brake Test Division of Clayton Mfg. Co. having designed Dynamic Brake Test Equiptment and Research Brake Dynamometers powered by motors as large as 400 HP.

I have Worked with the major Auto Manufacturers regarding "End of the Assembly Line" and "In the Field" Dynamic Brake Testing Equiptment.

I have worked with the US Goverment and several of the States regarding Brake testing and inspection for "In Service Vehicles".

I have been involved with Motorsports for many years and Vintage Road Racing where I have restored, and competed in Race cars equipted with both Disc and Drum Brakes. If you want to have a challange, try to get a Road Race Car with Drum Brakes to stop consistantly from the start of the race to the end.

I have worked on everything from an early '30s Indianapolis Race Car to a Modern Ferrari.

This is my background, what is yours????

AGAIN, I AM NOT SAYING ANYONE ELSE SHOULD DO THIS, THIS IS WHAT I DID AND THE RESULTS I GOT.

Chris
 
MikeK said:
A non-mechanical mod to shift braking to the front is to use woven linings in the front only, harder molded in the rear. Worked for me.
Click to expand...

This is certainly one way of improving the front to rear bias but in doing so, you have lost some of the rear brake performance and therefore you have less total brake effort for a given brake pedal force.

By increasing the length of the front levers, you not only improve bias BUT you also increase total braking effort for a given brake pedal force.

Again, This is just what I did and am not suggesting other also do the same. (Sorry, but I have to put a "Disclamer" in all my comments)

Chris
 
Before anyone jumps out and just starts modifying their cars let us think a bit about this.

Disclaimer: I am not saying this lever mod is good or bad. It certainly has technical merit, but I think it is not something the average guy wants to do as the brakes have to be done with attention to details as the front brake shoes have to be set up tight to the drums.

My first question comes from the comparison of any mod to original.
Does it really get you any worthwhile advantage in real life?

Do they really work better than factory?
We do not know for fact if any mods are better then factory.

We do know properly restored to original brakes work great.

There needs to be a quantitative set of data to determine if the changes are really anything good. Not just someone who thinks it works better then what they previously had experienced.

For example, using the same body or same type of body (weight distribution is important) one would first restore the brakes back to factory.
Then using a repeatable technique measure the brake power. The car would have to be run until the shoes were fully wore in to the drums. Once max braking is achieved with the factory set up, record the numbers.
Then change the levers and re run the tests.
Then change to the floaters.

Until these types of tests are run the ideas of changing the brake system are a nice novelty. All we know is a person changed the brakes and found them to work great- but compared to what? How much had the pedal travel and effort changed? Saying "it seems to be less pressure" is not very good, the person is comparing against what?

When compared to the fact just properly restoring the factory tolerances is known to give great brakes why complicate matters?
Lets be real. Many have troubles with just bringing the brakes back to factory. Most are doing band aid repairs and then throwing in some mods in hopes of better brakes. In the process skipping steps.


If real science was applied we might find the modified brakes are 10% less braking or only 5% more braking under certain conditions like running 65 MPH. At what point is it worth making the changes given how cars are driven?

Of course, the science may also find the mod significantly improves the brakes.

Again, I am not trying to knock CW's idea as it may be a very good idea.

I am just adding some perspective for all to consider. We should not be running out and changing stuff willy nilly just because one person did a change and he thinks it works great. (I am not trying to put down CW, just put perspective on a larger issue)


From a historical context. We know the A brakes are the Fords first attempt at a 4 wheel brake system. There were several variations during production. If you take the time to surf through the 1928 to 1939 service bulletins you will see the evolution of the Ford mechanical brakes. Ford did go to a floating brake system using wedges front and rear by the end.

The A brakes certainly were not the best that Ford could have produced.
They were learning as they go.
We know for FACT that properly restored the brakes are only limited by the small tire contact patch of the original tires.


Finally,
My opinions based on some facts:
The original mechanical brake system is the best choice if you are using the original wheels and tires.
A car with more HP, 16" wheels and radial tires would make me think seriously about going to hydraulics.
Hydraulics are not the best choice for cars that are not driven much. They will fail if not used frequently.
 
Thanks Chris for a thread about a totally new mod that stirs controversy. That's been missing here for a while. Now someone needs to start one about how they adapted a modern vacuum booster to the cross-shaft for mechanicals.:rolleyes:
 
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