<VV> Long and short brake shoes

[Dennis & Debbie Pleau]

When my employer sent me to brake school back about 1970, I learned a lot 
about drum brakes and not a lot about disks, because there weren't a lot of 
them around.

Back then, the primary shoe (front) not only had a shorter lining, but it 
was a completely different compound than the secondary shoe.  The primaries 
were usually a reddish color vs. a gray for the secondaries.  When you 
applied the brakes going forward,  both shoes move out just the same since 
they have the same sized piston.  When they contact the drum, the front 
shoe, rotates around because of the friction with the drum and transfers 
this rotation through the star wheel assembly to the secondary shoe, making 
it press much harder against the drum.  Since the top of the secondary shoe 
is against the pivot point it cant rotate.  On most stops the secondary 
shoe will push the piston back in and exert all the force against the 
pivot. The rotating friction which causes the front shoe to apply more 
pressure to the rear shoe is what is known as the servo action.

Now in this day where drum brakes are almost obsolete and asbestos is the 
worst thing ever mined, all the different compounds which were used for 
brake shoes are not available.  Their was no compelling reason to reproduce 
them in an non asbestos formula as most cars had gone to front disks and 
the change to FWD had begun.  A front wheel drive car does 90% of its 
braking with the front wheels, so the rear brakes don't need to be optimal.

That leave us with older drum brake cars a bunch of comprises.  For the 
most part we are stuck with a equal length shoes of the same lining 
material, Since the primary shoe isn't softer, it need to be longer to 
transfer the same (or maybe a little less) servo power to the secondary 
shoe.  The secondary shoe may not have as much friction with the drum as 
the old asbestos shoe would and will not have the same fade resistance.  On 
top of that the new compounds will wear drums faster.

One more note on linings, I was looking for linings a couple of years ago 
at my local FLAPS and NAPA had in stock some shoes in their line for 
classic cars, when I asked about the classic car designation I was told 
they were adequate shoes, not really for daily driving but adequate for a 
collector cars.  I passed and found shoes at CarQuest in there normal brake 
series for everyday driving.

Dennis
At 05:46 PM 4/8/2004 -0400, Ewell Mills wrote:
>I don't claim to be any expert on brakes, but thought I would throw in my 2
>cents worth.
>
>Back in the late 50's (when I was a whole lot younger) I replaced the brake
>shoes on my wife's 52 Kaiser. (Anyone remember those?).
>Of course auto adjusters were not available way back then.  Out of ignorance,
>I put the shoes on backward on all 4 wheels.  Couldn't hardly stop it in a
>ballfield.  Sold it to my Pa-in law who had the good sense to take it to a
>brake shop.  All they did was reverse the shoes (correctly) and it started
>stopping like it should. Incidentally, the shoes were not of equal length even
>way back then, so now I am more confused than ever.
>
>Cecil Mills
>Cocoa, Fl.
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