John,

It sounds like you've installed a leaky mastercylinder. The seals tend to dry out and fail when they are not immersed and swelled up by brake fluid. The symptoms you describe certainly appear to me as a bad MC (& not the rapper/hiphop type).

BenT

sent from my electronic leash

On May 29, 2011, at 12:07 PM, John Jensen <bluesbug@VERIZON.NET> wrote:

> I don't know how to diagnose my brake problem.  I changed master
> cylinders and bled the brakes already.  Anyway the basic symptom is if I
> pump them up and push hard the brakes hold pressure.  If I ease off on
> the pressure the slowly go to the floor.  Sometimes if I quickly push
> the brake pedal it goes to the floor, but a quick pump will make it hold
> the pressure.  There are more symptoms but that seems to be the main
> one. I don't see any evidence of leaking around the wheel cylinders.
> Now fact is I substituted an old master cylinder I had lying around from
> parting out van a few years ago. The symptoms from the replacement MC
> are more or less the same as with the one I replaced, except the one I
> replaced wouldn't hold pressure at all.
> Any clues or tutorials from the wise members of this group?
> 
> 1980 Aircooled Westfalia
> 
> John Jensen
> johnjensen@johnjensenartist.com
> http://www.johnjensenartist.com
> bluesbug@verizon.net