I really don't know anything about the BPV, however your problem is probably
improperly adjusted rear brakes or rear brake parts that are out of limits.
BTDT.  I have personally found that adjusting the rear shoes to the point
that they are just touching the rear drums is the proper adjustment.  I do
this by adjusting the shoes with the drum off.  Then putting the drum on (if
you adjust it so that the drum won't go on then you went too far).  Now step
on the brakes a few times.  Turn the drum.  Do you hear any dragging of the
rear break shoes?  If not remove the drum and adjust out a little more and
try again.  Do this until the shoes just bearly make a dragging sound.  Put
everything back together.  You should have high pedal and a great emergency
brake at this point.

I found this out when I had a really hard time adjusting rear brakes on one
of my vans a while back.  Several other folks on the list gave me this advice
and it worked great.

Thanks,
Ken Wilford
John 3:16
http://www.vanagain.com
Phone: (856)-327-4936
Fax: (856)-327-2242