Actually, the whole discussion isn't a matter of voting, it's a matter
of physics. Also, the question might be clarified if the "old fashioned"
terminology were used: forward ACTING shoe, and reverse ACTING shoe.
Here's the picture: You have a brake backing plate with the single
double-acting wheel cylinder mounted at the top, and the brake shoe
anchor pin mounted at the bottom. When the brakes are applied, the top
of the forward acting shoe, which happens to be toward the front of the
vehicle, is forced out by hydraulic pressure. Assuming that the vehicle
is moving in a forward direction, the rotation of the brake drum tries
to force the forward acting shoe to rotate in the same direction. This
can't happen because the lower end of the shoe is held stationary by the
anchor pin. Since the shoe can't rotate, the friction of the lining
against the drum forces the shoe even more tightly against the drum.
This is called self-actuation. Conversely, when the vehicle is moving
forward and the brakes are applied, the reverse acting shoe is pulled
away from the anchor pin (slightly) by the rotation of the drum,
resulting in NO self-actuation and very little braking effort. If the
anchor pin was on top, and the wheel cylinder was on the bottom (I've
never seen this), then the forward acting shoe would be mounted to the
rear of the backing plate and the reverse acting shoe would be mounted
to the front.
Since the vast majority of the wear on brake linings occurs from braking
while moving forward, it follows that the forward acting shoes have the
longer linings. Simple, eh?
As a matter of possible interest to some, some of the OLD Chrysler
products had two single-acting wheel cylinders on each of the front
wheels, each actuating a forward acting shoe (no reverse acting shoes on
the front), and the brakes still weren't worth a damn!
Ed Greeley
Mobile, AL
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