That's the thing about drum brakes. In the old old old days of relined shoes, there was a machine that would shave them. You'd measure the exact diameter of the drum then shave the pads (filling the area with asbestos fibers) to make the OD of the shoes match the ID of the drums.
Nowadays you install the new shoes into slightly larger drums... at first only the center of the shoes touch the drums since the radius' doesn't match. Think putting a small soup can into a big soup can then laying it on the side (same reason I like tight bearing clearances).
As time goes by the contact patch gets wider and wider. And the center of the new shoe may or may not have gotten overheated while it was doing all the work.
From my motorcycle ATV days I've found that beadblasting the contact area of the drum really helps. The brakes work much better and it helps to 'shave' the shoes to the right shape while smoothing the drums at the same time. That was the only way I could make little 50 and 80cc ATVs stop after doing a brake job to neglected drums.
Nowadays you install the new shoes into slightly larger drums... at first only the center of the shoes touch the drums since the radius' doesn't match. Think putting a small soup can into a big soup can then laying it on the side (same reason I like tight bearing clearances).
As time goes by the contact patch gets wider and wider. And the center of the new shoe may or may not have gotten overheated while it was doing all the work.
From my motorcycle ATV days I've found that beadblasting the contact area of the drum really helps. The brakes work much better and it helps to 'shave' the shoes to the right shape while smoothing the drums at the same time. That was the only way I could make little 50 and 80cc ATVs stop after doing a brake job to neglected drums.
