The Stovebolt Site Forums The Shop Area Engine Shop Brake Thumping...

THe brakes on my ol' 48 Chevy 3/4 ton work fine... so far... but about every third time I apply them I get a pretty good thumping through the brake pedal. What is this? Is it serious? And how to I remedy it?

It's a warped drum. You can have them turned by a machine shop for pretty cheap.

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
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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.

Why doesn't it happen every time I apply the brakes? And how can I tell which one it is, or do I need to have all four turned?

Thanks, Mechainiac... I'll check that first.

The only reason I can figure that it only happens intermittently is that the linings will sometimes grab the shoes and the other times (when it makes the pedal bounce), the linings are spinning with the drum.Strange but plausible.
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If you do not want to have the drums turned and there is no pedal surging from out-of-round drums, I would suggest roughing the surface of the drums with sand-paper (LIGHTLY) to give the inner drum surface a break-in finish and not a shiney glassy surface from the previous shoes.
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I know this is not a by-the-book job as required by any brake service shop,but it will work good if the drums are not out-of-round or if they have an uneven wear surface(bell-shape).
.BE sure to inspect for cracks and or heat-checked(small cracks in the surface)or hot-spots on the surface.

Having the brake-drums turned will cost between 8 to $12 each.It is worth it IF they need to be resurfaced.If the drums are worn OR machined too far already, the brake service shop will not turn them(they are regulated by laws).

Those shoes of yours should be rivited not glued. I know, I know!! The glue they use is really good stuff, but nothing beats riveting. Yes, they still do rivet brake shoes. If your shoes are indeed glued on, replace them with good riveted type shoes that a "truck" was meant to have. While you are checking that part of your brake system I would advise going the whole "nine yards" and going through the entire brake system.