If the wheel cylinder pistons move out on there own, that indicates air in
the system to me. 
Which also would explain a mushy pedal. 
If you work on 'any' brake, even just one rear, I would as a minimum also
bleed that brake. 
Brake fluid should be changed every two years. It's seldom done.
The very minimum to me, is bleed any brake you work on.
For example, I would never in a million years put in new front brake pads
without bleeding the front brakes.
Same for the rear, if you went in there to inspect - 
I usually empty out the dust, and often tweak up the self-adjusters a few
clicks.  The self-adjusters only keep them to about maybe 90 % adjusted, I
can get them closer than that without dragging.  Don't overdo it though-
things expand with heat.  
Then after I put the drum back on, I bleed that brake, always, just about. 

If you intend to work on your own vanagon, including brakes, you should be
able to bleed the brakes as handily and easily as you'd change a tire, like
no big deal.  There are tricks I use, nothing complicated, and
equipment.......a clear bottle with a clear hose, nothing fancy at all. 
But there are tricks to getting it right, bleeding by one person by
themselves. I'll post those if anyone asks. 
There are 4 brake bleeding methods I can think of off the top of my head.  I
use just the first two, and mainly only one simple 'by yourself' brake
bleeding method, and I get really firm pedals. Use Dot 4 brake fluid. If
your cheap, use Dot 3, but it's hardly worth it. Do not use silicone brake
fluid. Traditional brake fluid is just fine. 
Scott
www.turbovans.com 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Shawn Wright
Sent: Monday, September 17, 2007 10:26 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Causes of rear brake soft pedal

Tonight I replaced the rear shoes on my '88 Westy, which were last done by
the dealer about 100k km (60k miles), but more than 10 years ago. I have
receipts from the PO showing all new drums, cylinders, shoes, etc were
used. The rear wheel cylinders show a fair bit of corrosion, but no weeping
under the seals, and they do seem to have the springs to prevent creeping,
as they extended slowly on their own when shoes were removed.
With everything all back together, I still have the soft pedal syndrome,
where
one or more pumps is required to get a firm pedal. I was hoping this was the
rear wheel cylinders lacking those elusive springs. Front pads and calipers
are new in the spring. So the problem must lie in the booster or the master
cylinder, right? Tips on narrowing this down appreciated.

Thanks.
Shawn Wright
http://members.shaw.ca/vwdiesels
'88 Westy 1.6TD 5 speed
'85 Jetta Diesel 1.6NA