Front brakes questions

[Bob Johnson]

I am trying to better understand the operation of the original Model A brakes. Right now I am looking at the front brakes. I have a couple of questions about adjusting the brakes. I have ideas on possible answers but would like information from anyone who knows the details on why.

1) Most instructions on adjusting the front brakes say that the brake actuating arm should be angled forward 15 degrees. Why is this important?

2) Why is it important to "center" the shoes? How do you bend the roller track and still keep it parallel to the ground?

Hopefully I can figure out how the brakes work and use that to determine what are the important adjustments needed to get good brakes.

Bob

[Patrick L.]

1. If the lever is allowed to come back past vertical it loses mechanical advantage so it needs to start out forward of vertical.
2. These are not self centering or self energizing brakes. They should centered pretty well to allow proper shoe contact.

These are important adjustments as well as the wedge, the cross shaft, the rod length to fit the clevis' correctly.

[Purdy Swoft]

A 15* forward lean to the front brake levers allows the lever to pull through an arc. Pulling through an arc gives the needed leverage. Centering the shoes gives equal contact with the drums when the brakes are applied. If the shoes are way off center it will cause drag at one point or another inside the drum, or installation of the drum may not be even possible. I usually build up the tracks with welt and grind as needed to center the shoes. The older guys that worked on model A's in the day told me that they bent the tracks. Channel lock pliers work well. The tracks don't necessarily have to be parallel with the ground. The roller pins don't travel the full length of the tracks. The area that the pins move is what is important , where the brake tracks are concerned . If you study worn brake tracks you will see that the dipped or wear spots on the brake tracks are not that wide. I gas weld the worn spots on the tracks and proceed as necessary to center the shoes . A brake centering tool of some type will be needed. I use the one from Snyders PN A-2020 price $39.95 .

[Bob Johnson]

Please explain "pulling through an arc". The lever is always going to be pulled through an arc. Where it starts just determine where on the are it is pulled. How does 15 degrees help?

Bob

[George Miller]

The levers have maxim leverage when straight up. Ahead of or behind straight up, they act like a shorter lever. So when the brakes are fully applied they should be straight up.

[ericr]

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Originally Posted by Bob Johnson

Please explain "pulling through an arc". The lever is always going to be pulled through an arc. Where it starts just determine where on the are it is pulled. How does 15 degrees help?

Bob

supposedly it creates more leverage, I'm kinda like you, I wonder how much of an improvement it actually makes.....maybe somebody with an engineering background can sell the story better than me.

[Purdy Swoft]

I really should have known better than waste my time.

[Bob Johnson]

Purdy,

I do not think you have wasted your time. I am just trying to understand better what you have said.


Bob

[Joe K]

Originally Posted by Purdy Swoft

I really should have known better than waste my time.

Patience my friend.

Think torque wrench. You hold the wrench at 90 degrees to your line of pull - this way to get the MAXIMUM torque with the least effort.

In the case of the brake lever you start out AHEAD of 90 degrees so that when you reach 90 degrees your shoes are fully contacted to the drum.

Centering the shoes is more a function of placement ON the track rather than bending the track. You want the shoes to start equally distant from an imaginary center of action of the hub. This so the wedge can push directly down and not have to do any side to side weave and bob to self center. (although some self centering ALWAYS happens anyway.)

But best to start centered.

Joe K

[ericr]

Originally Posted by Joe K

Patience my friend.

Think torque wrench. You hold the wrench at 90 degrees to your line of pull - this way to get the MAXIMUM torque with the least effort.

In the case of the brake lever you start out AHEAD of 90 degrees so that when you reach 90 degrees your shoes are fully contacted to the drum.

Centering the shoes is more a function of placement ON the track rather than bending the track. You want the shoes to start equally distant from an imaginary center of action of the hub. This so the wedge can push directly down and not have to do any side to side weave and bob to self center. (although some self centering ALWAYS happens anyway.)

But best to start centered.

Joe K

the thing is, I don't think I have ever read how much actual travel there is to the brake rods.... could it simply be that positioning the lever forward creates more travel space for when the brakes get hot?

I'm in my foxhole and awaiting incoming rounds on this subject.

[160B]

Quote Posted by Bob Johnson"
Please explain "pulling through an arc". The lever is always going to be pulled through an arc. Where it starts just determine where on the are it is pulled. How does 15 degrees help?"



Visualize the brake actuating arm shaft cup where it contacts the operating pin. As the clevis arm is moved from the 15 deg forward to vertical the maximum mechanical advantage will occur when the clevis reaches vertical.

[Purdy Swoft]

Maybe I was quick to judgement. Anyway here goes again. If you visualize The front brake lever leaning 15* forward, The front and top of the lever will actually be at a lower point. As the brake rod pulls backward, the front and top of the brake lever will rise and move in a semi circle arc as it moves back to the point that the lever is standing straight up. This is the arc and leverage that I speak of. If the pull started from the straight up position , it would not pull through an arc. If the lever only moved straight back there would be less leverage and the brakes would be poor or non existant. I don't have BS credentials and this is the best that I can explain it. I didn't invent the arc term but do understand it.

[Barber31]

Purdy, if it makes you feel better to know , I haven't even looked at how the brake system works in there nor any of the mechanical parts that y'all are speaking of but with your description in your posts I can actually visualize what you are talking about.

[Bruskie]

good explanation. hope he gets it.

[Purdy Swoft]

Originally Posted by Barber31

Purdy, if it makes you feel better to know , I haven't even looked at how the brake system works in there nor any of the mechanical parts that y'all are speaking of but with your description in your posts I can actually visualize what you are talking about.

Thanks Barber !!! I try . I've worked on model A's for most of my life. I had to learn how to repair them myself, thats the only way that I could have them.

[Purdy Swoft]

Originally Posted by Bruskie

good explanation. hope he gets it.

Thanks Bruskie!!!

[Growley bear]

Originally Posted by Bob Johnson

Please explain "pulling through an arc". The lever is always going to be pulled through an arc. Where it starts just determine where on the are it is pulled. How does 15 degrees help?

Bob

Geometry. Once the lever passes vertical it assumes a drop over center position and has no mechanical advantage. In order for the brake rod to do its job, it would need to be repositioned. All adjustments and wear points in the Model A brake system are important. A properly installed and adjusted mechanical brake system on a Model A operates very well.

Chet