WHY "Self-Energizing" Drum Brakes Work So Well....

[V8COOPMAN]

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..... And Lockheeds SUCK Hugely!


Old Denny Odoms (our favorite"tubman" here on the 'Barn) kinda started this last night with a couple of comments in reply to a question by "SoCalCoupe" The question and tubman's reply were as follows:



"SoCalCoupe" asked:

Why are the Lincoln brakes better? I'm guessing they're just bigger and have a wider range of pedal pressure before they lock up.


"tubman" was absolutely correct with his short answer:

"Mainly, because they are self-energizing, unlike the original Lockheed types.

This means that the action of braking itself increases the pressure on the shoes, rather than relying on just your leg."


Well, that's when I just had to come-up with a long-overdue explanation of exactly what "Self-Energizing" brakes means. When it finally dawns on you just what all the excitement is about, it's clear as night & day why the "Bendix" (Self-Energizing) brakes are all the stir. So with all that, tubman is correct, but let's dig just a little deeper. This is a little tutorial of sorts that I stirred-up a while back in an attempt to make it more clear just how "SELF-ENERGIZING" (also known as "Bendix-type") brakes work. BELOW is a perfect example of a Lockheed - Ford "non-self-energizing" brake assembly. Simple as it gets with two shoes, each shoe fixed to rotate on a pin at the bottom. The top half of each shoe produces some friction against the drum, depending on how hard you can push.




Most-assuredly, there is NO "Self-Energizing" going on here.


Then, Bendix came-up with a revolutionary design that once you get the shoes to touch the drum and ROTATE (as an assembly) in the direction of rotation of the drum. Picture BELOW is of an early Bendix brake backing plate. I chose it to easily illustrate the pieces involved in an early, simple, Bendix (or "self-energizing") drum brake.





They will bolt to the early Ford spindles and early rear end with no fuss. Without the shoes being directly tied to the backing plate, the whole shoe mechanism is able to rotate in the forward direction of the drum as the shoes begin to expand at top and succumb to friction with drum. In this typical "Bendix"-type configuration, I figure the MOST important part of the whole assembly is the ANCHOR PIN. It is the TINY-Looking piece at the very top to which the two springs are hooked. Actually, the pin looks more like this picture BELOW.



When properly centered and locked-down in the CORRECT location on the backing plate, the pin is immovable. It also determines how far inboard the brake shoes will retract, as each shoe has a corresponding rounded surface which should match the proper geometry when the shoes are centered in the DRUM. In other words, there SHOULD be some provision for adjusting this pin upward, or downward BEFORE tightening in place.

After you watch this short video below, you will see how that pin allows no CIRCUMFERENTIAL movement of the REAR shoe. The REAR shoe can only be jammed into the rear half of the drum by the FRONT shoe being rotated by the forward rotation of wheel. The REAR shoe cannot be rotated because that pin restricts the rotation of the REAR shoe. Rear shoe's friction surface just gets pushed harder and harder into the rear of drum's stopping surface. Click the link BELOW for short, 3-minute video - THE MOST-IMPORTANT PART. Easy-peazy!

https://youtu.be/n0OFhyxo4As


Coop

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