Re: Dan's emergency brake again

[jlandry@domain.elided (John A. Landry)]

In a brilliant stroke of genius, cookiedan@domain.elided (Daniel Nees) blurted
out:

>   The rear shoe of the Scout drum brake is the e-brake shoe. (Or is it
>the front one?) Either way, it is the shoe that is never worn down when
>you replace your brakes and the one that you always put in the wrong
>spot the first time.

Dan,

This statement is not technically accurate either.  There's no such thing
as the e-brake shoe.  However, I can see why you might want to call it that
because the lever that the parking brake cable is attached to is on the
*secondary* shoe.  The other shoe is called the *primary* shoe.

The parking brake lever works by forcing the parking brake strut against
the *primary* shoe (the shoe opposite the lever).  The strut in turn pushes
the primary shoe against the drum.  At the same time, the parking brake
lever also forces the secondary shoe against the inside of the drum through
a camming action on its pivot point.  The net effect is a "spreading" of
*both* shoes equally against the inside of the drum... not just the one
shoe.

However, when you apply the regular brakes in a moving vehicle, the primary
shoe is forced "primarily" against the inside of the drum and the rotation
of the drum helps to further wedge it in tight.  The rotational movement
and wedging of the primary shoe is transferred to the secondary shoe
through the adjuster assembly, which in turn causes it to get wedged
against the inside of the drum even more so.

Because of this inherent shifting and wedging action of the brake shoes,
the *secondary* shoe performs most of the braking action and wears faster.
Since the parking brake lever is attached to the secondary shoe and here
the wear is the greatest, one might be led to believe only the secondary
shoe is used for the e-brake.  This is simply not the case.  Both shoes
play an equal part when the parking brake is applied.

Take care,

John L.
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