The spec is to grind the shoes .010 to .024 UNDERSIZE of
the drum so that they contact at the center of the shoe arc first and then are
hydraulically pressed to a full contact fit. From there during wear they
theoretically remain about the same and wear evenly for their life.
If they were ground to the same size as the drum they
would then tend to be forced out at the outer ends and loose most of the center
arc contact. Since most replacements were never arc ground, we have
seen this wear at the outer ends over and over on cars we've worked
on. Such brakes were not doing their job across much of the
shoe. The result is ongoing complaints of bad brakes ongoing 50 years
later.
For clarification, I've only personally found that
grinding spec in a '57 DeSoto tech service bulletin although it almost certainly
is the engineering standard intended for all center plane Mopar brakes and must
have been elsewhere in print. Anyone else support that from their
library?
W
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