Hi there,
I would say that it could be either one.  I'd pump up the pedal, and hold
solid pressure against it for a while--if the pedal slowly drops away, I'd
suspect the master cylinder.  If not, I'd look to bleeding.  You should
renew the fluid every two years anyway, so look at is as a chance to kill
two birds with one stone!
As to procedure, do you have a Bentley?  If not, I'll email you their steps.
bmc  :)
"Faith will move mountains, but you'd better bring a shovel...."

> From: John Lunetta <blun1432@OPTONLINE.NET>
> Reply-To: John Lunetta <blun1432@OPTONLINE.NET>
> Date: Thu, 28 Feb 2002 15:48:06 -0500
> To: vanagon@GERRY.VANAGON.COM
> Subject: help ; brake bleeding
>
> Does any one know the procedure for bleeding the brake system on a 1990
> vanagon gl, w/power brakes?
> I replaced the rear brakes, Drums, shoes, hardware, the whole thing. But I did
> not open any lines, I still can't get a high pedal, and I adjusted the shoes
> to fit the drum. If a pump the pedal it comes up but as soon as I aply the
> brakes the next stop the pedal goes nearly to the floor. I have replaced the
> rear brakes in the past and this never happend. Does it sound like I need to
> bleed them, or is my master cylinder bad. Any ideas would help. Thanks, John
> 1990 vanagon gl
>