Like you didn't already know, Rear brakes self-adjust poorly Options

[mskala]

Even though I have a Garretson proportioning valve that keeps the
pedal feel pretty good, there's always a bunch of free play before
the brakes start really working.

Anyway, I had an excuse to get into the rear wheels, and I adjusted
all the adjusters like 1/32 of a turn back from where they grab the
wheels. The pedal free play was much much less and all was right
with the world. Of course about 3 days later we did the autocross,
and by the time I was driving home the excessive free play was back.
. (IMG:style_emoticons/default/smash.gif)
(IMG:style_emoticons/default/headbang.gif)
If this wasn't a street car in a stickler inspection state, and a sort-of
'classic' car that I want to keep close to normal, I'd go to a real rear
caliper design.

[SLITS]

I set 0.004" and they stay great for a period of time. I didn't look, but you're running a /6 - the pistons are a few mm larger and put more pressure on the pads. Maybe they just wear faster. (IMG:style_emoticons/default/confused24.gif)