| Re: [GMCnet] Primary and Secondary brake shoes [message #320641 is a reply to message #320636] |
Tue, 18 July 2017 08:35   |
emerystora
Messages: 4442
Registered: January 2004
Karma:
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Senior Member |
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> Servo and self-energizing action is produced by the hooking the heel of the primary shoe to the toe of the secondary shoe. When the wheel cylinder forces the top ends of the shoes out against the drum, the forward shoe will tend to stick to the revolving brake drum and be carried around with it. As the primary shoe attempts to revolve, it will jam the secondary shoe against the single anchor pin. This stops both shoes and produces a binding effect that actually helps the brakes shoes apply themselves. This servo and self-energizing action reduces the amount of pedal pressure necessary.
>
> The primary shoe on self-energizing brakes generally has a smaller amount of lining. The primary lining is usually also of a different composition. The secondary shoe does more of the braking, and less is needed on the primary shoe."
>
> The secondary shoe always faces the rear of the vehicle
>
> If the shoes are accidentally reversed, there will be adverse wear, more pedal pressure required and poor braking.
>
> So, if any of you are doing your own brake work, remember "Big pad to Back”.
The last issue of the GMC Motorhomes International magazine had an excellent article on this. (I wrote it!).
Emery Stora
77 Kingsley
Frederick, CO
> On Jul 18, 2017, at 6:27 AM, Wayne Rogewski wrote:
>
> Morning to all.
>
> I reviewed my MM and parts book. As we know there is a primary and secondary brake shoe. One has more friction material than the other. I forget at
> the moment which one is called the Primary.
>
> The first drawing with the exploded view in the MM appears to show the shoe with more material on the left side when looking at it (presumably toward
> the front of the coach) with the other shoe, with less material toward the rear of the coach. Is that the correct placement for the shoes?
>
> Ive see a few other photos and it appears the reverse. The parts book, while a drawing not a photo appears to show the shoe with more material
> toward the front of the coach as well.
>
> Just wondering before I put it all back together. I have to believe it makes a difference otherwise all the shoes would be identical.
> --
> 77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
> Mid Michigan
>
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