Jeff,

I'm pretty sure the front and rear circuits are independent on the master
cyl, so that if the rears have a problem, you will still have the fronts and
vice versa. The front portion of the piston in the ms is for the front
brakes and the second half of the piston is dedicated to the rear circuit.
   If your van is pulling while braking, it can be several things:
    1) friction variances on the rotors, ( make sure both are turned , just
to clean
       them up evenly. install new pads
    2) caliper piston binding, probably coroded, try rebuilding them, it's
easy
    3) possible worn ball joints
    4) possible worn tie rod ends. if bad I think you can install 911 turbo
tie rods

It sounds like caliper error

Malibu Tony  85 Westy.....Jeff email me and I'll tell you where to get some
calipers cheap.

Date:    Sat, 17 Mar 2001 07:50:03 -0600
From:    Larry Alofs <lalofs@ENTERACT.COM>
Subject: Re: Brake pedal pumping/master cyl Q

Jeffrey R wrote:

> But if the master cylinder is going or leaking internally are there
"zones"?
> Meaning would only the right front caliper and left rear shoes work and
would
> that cause a pull ro one side?
>
> Truth is I think I got off too easy adjusting the rear shoes--so how do I
> check the master cyinder and how to I check if the right is braking harder
> than the left?
>
> Any education appreciated.
>
> TIA
> Jeff
> 83.5 Westy
> LA,CA
>

Find a gravel surface.  Open the windows so that you can hear when the
wheels are
sliding.  Try some hard stops from various speeds.  By checking the skid
marks,
you can tell which wheels are locking up first.
  I may be wrong, but I believe that the "zones" are front vs. rear rather
than
the diagonal system used in other cars.  Comments anyone?

Larry A.