Cripes Barney. What the hell do you do for a living? I have never met
anyone who is so car-oriented in my life. Very eloquent elaboration.
I wonder if the Triumph list has a mental - powerhouse like Mr. Gaylord.
I'm glad he's on our team.
Thomas James Pokrefke, III
pokrefke@netdoor.com
Audentes fortuna iuvat
Barney Gaylord <barneymg@ntsource.com> wrote (and I quote):
> At 07:46 PM 9/4/99 -0700, Bud Krueger wrote:
> >.... The shoes are asymmetric, i.e., .... There is more shoe showing at
> one end of the lining than at the other. ....
> >
> >Long story short .... The part of the shoe with the most metal not covered
> by the lining, i.e., the part with the tapered ends goes into the adjuster
> side toward the front of the car. ....
> >
> >.... I'll bet that Barney can give us a good explanation about why ....
>
> Why sure, glad to be of assistance. Thought you could catch me on this one
> late at night, huh? Brace yourself.
>
> Forward motion of the car being most common, think of drum rotationin that
> direction. Drum brakes by their nature are self-energizing. When you
> apply the brakes, the force of the hydraulic cylinder pushes the shoes out
> against the drum. Friction between the drum and the shoe wants to force
> the shoes to rotate in the same direction as the drum, so that force is
> going in a circumferencial direction along the surface of the drum. The
> anchor point for each shoe is an inch or so inside of the drum. For the
> leading shoe this is bearing against the adjuster. For the trailing shoe
> this is bearing against the abutment at the top. The distance between the
> anchor point and the inside of the drum is a mechanical lever arm that
> creates a rotational force on the shoe, wanting to rotate around the anchor
> point, so the shoe wants to push outwards more against the drum. This is
> the self energizing affect.
>
> Now lay a right angle with one leg running through the anchor point and the
> other leg being always tangent to the drum. As you move this arrangement
> around you notice that at tangent points farther from the anchor point the
> tagent leg is more distant from the anchor point, making a longer lever arm
> for the circumferential force to work on. That means that the end of the
> shoe farther from the anchor point sees a little more force against the
> drum, while the end closer to the anchor point gets less force against the
> drum.
>
> Locating the friction pad more toward the far end of the shoe effectively
> puts more area of lining there where the force is higher, and less lining
> at the end near the anchor point where there is less force. This should
> lead to more even wear on the lining. If not for this arrangement the end
> of the lining farthest from the anchor point would wear faster and get down
> the the metal base first. As the linings are shot when the thickness
> anywhere along the length approches nil, even wear along the length is a
> noble goal.
>
> Did anyone actually understand that? The idea here is that when you
> understand the function you don't have to go looking for the pictures any
> more to get the proper orientation.
>
> Barney Gaylord
> 1958 MGA with an attitude
> http://www.ntsource.com/~barneymg
>
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