The purpose of the added spacers is to increase the size of the contact
patch. If you look at a bunch of Vanagon rear brake wear patterns like
some of us have it becomes apparent that most of the friction material
never gets used and the shoes wear out only at the far end away from the
fixed pins. Shimming the fixed pins out improves things. The result is a
better match between the two curved surfaces as the shoes wear in.

It has been a few decades since I had any brake shoes arced to match the
drums. That is something that used to be commonly done. But we used to
also replace just the friction linings on the old metal shoes too, and
along with that went the need to match the curve of the new linings to
the drums. In particular this was most essential on front drum brakes.

Mark

Mike Riley wrote:
> it seems to me if the linings are thinner and the metal parts are the same then the brake shoes have the
> wrong radius and this would result in a smaller contact patch. In the old days you could get the shoes ground to the  exact curvature of your drums. all high end shops did this.
> thanks
> mike
>