FT: Frame (Twin) New 7" Brake Shoes

Chris Launders

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Would there be an advantage using elliptical instead of flat cams ?
I'm sure some clever programmer could work out a shape and the force applied to the shoe.
 

vibrac

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As regards the H48 one of the few good design features of the AMC line is the pad at the shoe/cam interface
1584783173123.png
There is not a lot of meat in a vincent shoe end but I wonder if an option like this is possible/
 

Bill Thomas

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I would have thought the longer lining would get rid of heat better ?,
So you could use a very soft lining ?,
Or we would all be using linings about 1/2" long ?.
If I can find some money, I would give it a go.
 

Vincent Brake

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Hi David,

In your drawing;
The forces on the brake are true only, if you have a standing still brake drum.

Its a total different situation when you let that one roll
Than you see the Trailing/Leading effect.

Specially the leading one should have its lining as far possible to the cam side.
 

davidd

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Vincent,

I should have been more specific about the source of this material. This is not my work. It is the work of Newcomb & Spurr, who were the top engineers at Ferodo. It is in their book: Braking of Road Vehicles.

The pressure lines are a relatively accurate drawing of the pressure on a fully lined leading shoe in motion. If there were a corresponding trailing shoe in motion opposite the leading show it would look the same, but the force lines would be only about 1/3 the length of the leading shoes. The drawing is done to demonstrate the relative difference between the center of pressure and the areas of lower pressure on the same shoe. It does not show the difference in pressure between a leading and trailing shoe.

Brakes_simplex_SLS_explained.jpg

This is a good example of the difference between leading and trailing shoe forces. on the left is a pivoted system. I think it is a good example of showing that when you trim the lining back you do not lose a lot of force, but you certainly start to "square it off" in terms of the graph. Volvo did not like the wear in the leading shoe, based on their scheduled service intervals. By tuning the lining (cropping it back at the leading edge) they decreased the servo action of the leading shoe and made the wear on the shoes a bit better. This is also a rear brake and manufacturers tend to detune the rear brakes, on motorcycles particularly, to keep the rear braking at a minimum.

There is nothing wrong with wanting the lining as long as possible at the cam end even though the maximum force is closer to the pivot end. Instead, at the cam end, of a leading shoe you have some control of the servo effect. It is difficult to get too much servo effect, but when you do the front brake will be
dubbed "grabby". The compromise is usually in the lining material. It is difficult to make low friction lining grabby.

Would there be an advantage using elliptical instead of flat cams ?
I'm sure some clever programmer could work out a shape and the force applied to the shoe.

Chris,

The cam design of the Vincent is difficult to work with because it is flat. Because it is flat, it lifts each of the shoes to different heights and pressures. On the front, the lift favors the leading shoe. On the rear, the brake arm is turned so the lift favors the trailing shoe. This is part of the detuning the rear brake that I mentioned.

The shape of the cam can be changed to an equal lift and pressure using an "S" involute cam.
3-s2.0-B9780750651318500129-f11-14-9780750651318.gif


I do think you could fool around with the shape of the stock Vincent cam and get some beneficial effects. Many years ago an owner from Chicago named Wozney, if I remember correctly, came up with a design.

David
 

oexing

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VOC Member
Sorry for showing another BMW part, they have come up with a redesigned brake cam for their twin leading shoe brakes in the fifties and used this up to /5 series drums as well. No steel capped shoes used, no need for that. The motion is mainly lifting the shoes, only minimum rubbing effect. The shoes are same but cams are different because no rod link between cams with push/pull operation cable outer and inner. I am planning to do four leading link 200 mm brakes with these shoes. In the photo two new shoes laid over a used brake set.

Vic
P1050633.JPG
 

Vincent Brake

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Vincent,

I should have been more specific about the source of this material. This is not my work. It is the work of Newcomb & Spurr, who were the top engineers at Ferodo. It is in their book: Braking of Road Vehicles.

The pressure lines are a relatively accurate drawing of the pressure on a fully lined leading shoe in motion. If there were a corresponding trailing shoe in motion opposite the leading show it would look the same, but the force lines would be only about 1/3 the length of the leading shoes. The drawing is done to demonstrate the relative difference between the center of pressure and the areas of lower pressure on the same shoe. It does not show the difference in pressure between a leading and trailing shoe.

View attachment 32969
This is a good example of the difference between leading and trailing shoe forces. on the left is a pivoted system. I think it is a good example of showing that when you trim the lining back you do not lose a lot of force, but you certainly start to "square it off" in terms of the graph. Volvo did not like the wear in the leading shoe, based on their scheduled service intervals. By tuning the lining (cropping it back at the leading edge) they decreased the servo action of the leading shoe and made the wear on the shoes a bit better. This is also a rear brake and manufacturers tend to detune the rear brakes, on motorcycles particularly, to keep the rear braking at a minimum.

There is nothing wrong with wanting the lining as long as possible at the cam end even though the maximum force is closer to the pivot end. Instead, at the cam end, of a leading shoe you have some control of the servo effect. It is difficult to get too much servo effect, but when you do the front brake will be
dubbed "grabby". The compromise is usually in the lining material. It is difficult to make low friction lining grabby.



Chris,

The cam design of the Vincent is difficult to work with because it is flat. Because it is flat, it lifts each of the shoes to different heights and pressures. On the front, the lift favors the leading shoe. On the rear, the brake arm is turned so the lift favors the trailing shoe. This is part of the detuning the rear brake that I mentioned.

The shape of the cam can be changed to an equal lift and pressure using an "S" involute cam.
View attachment 32971

I do think you could fool around with the shape of the stock Vincent cam and get some beneficial effects. Many years ago an owner from Chicago named Wozney, if I remember correctly, came up with a design.

David

Mmm David, i dont believe all thats written.
I do belive the force normally thoeratically applied to the shoe will create an even force over the surface, n than when elasticity in materials are taken into account the middle would have less force left.
As its not more than a beam onto two points.
Thats where the original vinnie brakes fail.
But its not a true two points its laying on.
There is a great deal of dynamics going on here.

I will dive into my old design notes to show later.
If i remember it still, to do later.
Or did that come sooner.....

Cheers

Vincent
 

oexing

Well Known and Active Forum User
VOC Member
This s-shape cam would require hardened rollers on the shoes, otherwise there would be a LOT of friction in the motion, some complication. The BMW shoes have been proved for decades to work allright, even no steel caps necessary as only minimal rubbing effect, mainly lifting. So my choice for own brakes in my brain.

Vic
 
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