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Date:         Wed, 16 May 2012 17:06:47 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Recoined Brake Shoes. Means: Arced ?
Comments: To: neil n <musomuso@GMAIL.COM>
In-Reply-To:  <CAB2Rwfh=-3CuwatLSUdKGQq9FFqcOsaGMxfj7Fa=2Kp8KHsfDw@mail.g
              mail.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 01:09 PM 5/16/2012, neil n wrote: >think the wear patterns indicated that the top 1/3 of shoes were contacting >drums but I haven't looked in some time.

Look in the archives for Dennis Haynes' discussions on spacers for the bottom pivot.

If the lining material is of constant thickness, there's no possible way for it to have full effective contact throughout its life in a setup with a fixed pivot point. Whatever point touches first will start to wear in a small patch which will gradually spread as the brakes wear in. The better the initial fit, the larger that initial patch (or perhaps two patches) will be. Perfect fit requires that the lining radius of curvature precisely match the drum in its present condition of wear, and that the pivot be shimmed until as nearly as possible the entire lining contacts the drum simultaneously when the brakes are applied. This will quickly wear into full contact. At the end of service life the cylinder end of the lining will be worn to minimum thickness, while the pivot end will be considerably less worn. The cylinder end of the lining will always do more work, and because our brakes are set up in a leading and trailing shoe arrangement the shoe where the cylinder end faces the oncoming brake drum will do more work.

Back when drum brakes were used for front wheels where most of the work gets done and cars didn't have vacuum-assisted brakes I believe they had more elaborate arrangements for some, with double leading shoe setups with (I presume) two cylinders and such; and there were brake shops that would individually fit shoes to drums and so forth. And my grandmother's (late '50s/early '60s) Studebaker had band brakes.

The (front) disk brakes on my Saab 96 took this wear thing to an extreme. They were Lockheed brakes, single-cylinder with a pivoting instead of sliding arrangement, and new pads looked like a ski slope. When they wore down to level, they were used up.

Yrs, d


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