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Primary vs secondary brake shoes


dep5

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The early (pre1935) Chrysler owners manuals and parts books show the long shoe forward and short shoe to the rear. These cars used a thru-bore wheel cylinder with each shoe anchored at the bottom.

This flies in the face of the conventional practice of short (primary) shoe forward and long (secondary) shoe to rear.

I wonder about other cars of the era . . .were the early references wrong 'in the day' or did theory evolve?

Edited by dep5 (see edit history)
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I believe that the difference is in the mechanical setup of the shoes:

On the Lockheed (Chrysler products) each shoe is anchored at one end. The front shoe will tend to be pulled out by the drum rotation (the primary) and rear shoe pushed back (secondary). Except, of course, on those vehicles equipped with two single acting wheel cylinders where, I think, both shoe would act as "primary shoes".

On Bendix style (typical newer stuff) the shoes are connected so that the rotational force will tend to put more force on the rear shoe. Basically once the shoes meet the drum they tend to be self-energizing, wrapping in the direction of drum rotation and loading the rear shoe more than the front. Chrysler did not like this, at least according to their advertising, as it tends to make the brakes grabby.

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