I had the same thing happen to me on my wifes 52 GMC .The brake lining had came unglued from the metal part of the shoe.It would work fine one time you stepped on the brakes and then it would make the pedal hammer your leg the next time the brakes were stepped on eek eek
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When I pulled the rear drum,the shoes were nice and shiney,,,,but no lining and no groves or grinding marks.I looked in the drum and both linings were sitting in the drum(Complete!!!).they were only slightly chewed up on the ends of the linings.
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I installed new shoes and went on my way.
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4onthefloor,,, the brake pedal would not have an intermittent thumping or pulsation if it was a warped drum, it would be consistent. cool

There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us.
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Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!