Well I stand corrected. Apparently they do adjust in the reverse direction in addition to going forward. The Dexter site has very little in explanation but here is what I found:
Self Adjusting Feature
(Not available on all sizes)
Dexter electric brakes may be equipped with a forward self-adjust feature. This will allow the brakes to adjust on both forward and reverse stops. Brake adjustment occurs when lining wear results in enough gap between the shoes and the brake drum surface. This added clearance will allow the adjuster mechanism to rotate the screw assembly at the bottom of the brake. That action expands the distance between the shoes and thus closes the gap to the drum
surface.
Ref: Page 6 of
https://www.dexteraxle.com/docs/defa...4.pdf?sfvrsn=0
