Hi folks, here is my last take on clutch bleeding and fluid reuse. First of
all, there is no reason why "clean" brake fluid can not be recirculated in
a "clean" system. The fluid does not decompose or interact chemically with
any other substance and thus remains chemically stable for quite some time.
The fluid eventually absorbs water and thus losses some of its hydraulic
properties and is no longer inert to system materials. As far as the fluid
goes, it does not remain static inside the system. By design hydraulic
systems are dynamic and every time you press the pedal the fluid moves
inside the system, interacts with the system walls and moves around itself.
Recirculating fluid is thus safe as far as the chemistry of the fluid.
Lets talk particles, there are three important particles that contaminate
the system. Oxides from the system, dirt (in the form of dust, soil, etc)
and micro bubbles. How can you remove these? filtration. I would recommend
to put a filter on the end of the pipe that goes back into the system from
the nipple. Since I have access to laboratory materials I have managed to
use a VW gas tank mesh filter made of polyethylene with Whatman filter
paper No.1. This step will trap most all dirt of significant size that can
cause brake problems and also coalesce micro bubbles. I believe that
flushing the system before doing a serious bleed is of utmost importance.
Recirculation done safely and properly with a good final filter is possible
and can be a safe and fast way to bleed your brakes and clutch. Enrique