Brake Adjustment

[Tom Wesenberg]

What are 'original 4 wheel parking brakes'?

The early 28 Model A's didn't have seperate emergency (parking) brake linings, and the parking brake handle pulled on the same crosshaft that the foot brake pulled on, so when you set the parking brake you set all 4 wheels.

 

[Marco Tahtaras]

The point that some of us are trying to make is that in the last 80 or so years, we have learned something more about braking. Between the T and the A, we learned that you can actually HAVE front brakes. Since then, we have learned that setting the fronts to lock first is better and safer.

Steve

Anyone that knows brakes (and simple physics) understands that to be a fact. However it's a moot point with original brakes as it can't be changed with adjustment.

BTW, drive an A every day including in heavy rain as I did 35 years ago and you will learn very quickly.

 

[SteveM]

...as it can't be changed with adjustment.

Please explain.

If you can adjust the bias rearwards so that the rears lock up first, then you should be able to go the other way.

Steve

 

[Ross/Kzoo]

Thanks "modelaer". I had never thought about the fact that the rear lever arms are longer and therefore exert a different force as they are applied.

 

[Tom Wesenberg]

Plus since the rear brake cam has a floating pin I would think it is more self energizing than the fronts.

 

[SteveM]

OK, I see the point about the rear vs front levers and the floating pin (I didn't realize that one), but the process is still adjusting so that the rears come on first. If we adjust so that the fronts come on first, then there will be more braking in the front, no?

I'm not trying to be think-headed, but I'm still not getting why we can't improve the braking by making the front wheels share more of the load.

Steve

 

[anut]

hey guys and gals drive thes old fords 35 to 40 like ford made them to do and you wont have any brake trouble enough said

 

[Marco Tahtaras]

Plus since the rear brake cam has a floating pin I would think it is more self energizing than the fronts.

Somebody published an article some years back claiming the equalizing cam on the rear was "self energizing" and doing something similar on the front would accomplish a similar effect. This is not true. For a two shoe system to be self energizing it must have a floating heel.

The reason the brake bias is toward the rear is simply a leverage issue. The front brakes actually actuate at a faster rate (more motion per inch of pedal travel) than the rears. However the result is less leverage (more pedal pressure required).

If you attempt to adjust the front brakes to come on earlier you begin to defeat the rear brakes and the brake pedal becomes stiff (front shoes already seated) before the rear brakes can do their job.

In 1932 Ford changed the leverage to an equal 50/50. If I recall correctly they said to adjust the brakes so all four would skid under hard braking at 25 mph. Having a specific speed was a necessary point of reference. The faster the car is traveling, the greater the weight shift toward the front under hard braking. Assuming you could lock the tires a slow speeds, the fronts would lock first below 25 mph. Over 25 mph the weight shift would be sufficient for the rear brakes to skid first.

As a side note, many folks express significant improvement adding an equalizer to the front brakes. This is simply due to the fact that VERY FEW folks ever get close to having the shoes positioned equally within the drum much less centered up and down. Anything that does either job for them makes a significant improvement.

The 40/60 brake bias in a Model A is rarely an issue as the brakes are pretty amazing when working as they should. However panic stopping on a rain soaked road requires some driving skill to keep the car facing forward.

 

[Paul from Maine]

Here we go again. I am not going to discuss the merits of front brakes locking before rears. We are discussing the Model "A" Fords here. Unless someone can show me a specific Model "A" Ford Service bulletin that supersedes the 1928 and through 1931 issues with a major change in brake adjustment method then, any modifications beyond that is not recommended and can have all sorts of ramifications as pointed out earlier. If one is going to adjust brakes in an un-recommended method, then why not just put in hydraulics?

Pete

Sorry, but I was trying to correct the misinformation about being able to steer with the front wheels while the rear brakes are locked. Maybe a professional driver can, but most normal drivers can't. If they think they can, then they are under the misconception that their rear brakes are locked when they really are not. The physics just won't allow it. I was concerned that someone was suggesting to Model A drivers that it is better to have your rear brakes lock up first than the fronts. This is dangerous, and perhaps lethal advice. I own three Model T's and understand the ramifications of locked rear brakes oh too well. And before someone tells me that is impossible with a transmission brake, don't forget the "improved Model T of '26 and '27 came with 11 inch drums and fabric lined shoes in the rear, plus a much wider brake drum in the transmission. Applying the emergency brake along with the pedal can lock 'em up good. Plus the front wheels have no brakes.

 

[Bruce Adams]

Show me where there is a bulletin that supersedes the owner's manual requirement to put only "clean fresh water" in the radiator


Steve

Gee, my "MODEL A INSTRUCTION BOOK" says "In freezing weather it is necessary to use an anti-freeze solution in the circulationg system to prevent freezing of the water, and bursting the tubes in the radiator."

 

[Jim Parker Toronto]

"What are 'original 4 wheel parking brakes'?"

I have an Early 28 Roadster. (some call them AR's) When I pull on the E-brake handle, it activates the Service Brakes, and all four wheels will be locked. I do not have a separate brake system located in the rear wheels. The drums on my car are interchangable front to rear. (not the hubs of course)

 

[David Cockey]

Somebody published an article some years back claiming the equalizing cam on the rear was "self energizing" and doing something similar on the front would accomplish a similar effect. This is not true. For a two shoe system to be self energizing it must have a floating heel.

......

I seem to recall a discussion involving both of us and others on the Ahooga forum nine or ten years ago about the effects of adding brake equalizers to front brakes. At the time I did an analysis and determined that the brakes were more effective with the bottoms of the shoes floating rather than fixed. My recollection is it was due to non-linear way "self energizing" works. The front shoe brakes less but the rear shoe brakes even more and the net is increased braking for a given pedal force. I'll try to find time to go through it again but it won't be in the next several days.

 

[Tom Wesenberg]

I seem to recall a discussion involving both of us and others on the Ahooga forum nine or ten years ago about the effects of adding brake equalizers to front brakes. At the time I did an analysis and determined that the brakes were more effective with the bottoms of the shoes floating rather than fixed. My recollection is it was due to non-linear way "self energizing" works. The front shoe brakes less but the rear shoe brakes even more and the net is increased braking for a given pedal force. I'll try to find time to go through it again but it won't be in the next several days.

I've been thinking about Marco's statement about the floating heel. It seems to me the heel of the top shoe is floating due to the cam and rollers, therefore the friction on the top shoe should add braking effort to the bottom shoe with it's toe also floating on the cam and rollers.

 

[Marco Tahtaras]

I've been thinking about Marco's statement about the floating heel. It seems to me the heel of the top shoe is floating due to the cam and rollers, therefore the friction on the top shoe should add braking effort to the bottom shoe with it's toe also floating on the cam and rollers.

Keep in mind, if the upper shoe drags on the drum and shifts forward it is no longer seated at the heel. If it is no longer seated at the heel then there is no tension against the drum at any point except the toe. You would in fact loose active surface area. Also you would clearly see this in the long term wear pattern of the upper shoe as the majority wear would be near the toe.

Even if you were talking about only a few thousandths shift in the upper shoe would likely have a "grab and release" chattering effect. Now, let's assume what I say is incorrect. How much motion is required to "energize" the second shoe? There is only .015"-020" shoe clearance at the toe. When the brakes are applied this clearance is gone. How much motion of the first or "primary" shoe is required to apply pressure on the secondary shoe? .005"? .010"? Most folks are running at least that much clearance between the front brake wedge and the wedge stud so any such impact would be similar on the front if the shoes are properly centered.

For those interested, below is a little additional history on Ford mechanical brakes.

 

[skip]

skip.
http://i259.photobucket.com/albums/hh299/1930fordroadster/Coupleoftricks-1-1.jpg

 

[V4F]

ive had my floaters for like 5 yrs & love em ................. no scientific reason , just how they work ............... steve

 

[FlatheadTed]

I did some calculations on the shoe movement at the wedge end ,verses the clevis moment the shoes move 3 -1/16 to one inch of clevis arm moment the front is the same as the back ,The rashio front to back is determined by the equalizer bar or cross shafts clevis arm length or the ratio between the two .On the rear brakes its 100 mm long on the clevis arm on the bar its 70 mm this is a reduction ,On the front its 65mm on the bar and 60 mm on the front clevis ,Because on the bar its longer this brings the front on first ,I agree with Steve you can change the bias front to back ,The 37 Ford relied a lot on the springs to give the self energizing affect. The photo on the right is a self energizer on a 34 Chev (not joined at the heal ) there were many forms of self energizers around in the 30s ,as far as I can tell Ford didn't use them because he did not want to pay royalty's,

 

[rons49]

That is why I said "here we go". Thanks Marco for showing the 1932 bulletin:

In 1932 Ford changed the leverage to an equal 50/50. If I recall correctly they said to adjust the brakes so all four would skid under hard braking at 25 mph. Having a specific speed was a necessary point of reference. The faster the car is traveling, the greater the weight shift toward the front under hard braking. Assuming you could lock the tires a slow speeds, the fronts would lock first below 25 mph. Over 25 mph the weight shift would be sufficient for the rear brakes to skid first.

 

[ericr]

has anyone besides me ever seen a historical reference in one of the Clymer books from years ago to the effect that Mr. Ford opposed front-wheel brakes on the Model "T" because he believed the had a tendency to grab and lock up?