Tom Del Rosso wrote:
"John R. Carroll" wrote in message

"DrollTroll" wrote in message
...
I seem to remember something called a "proportioning valve",
between front and rear brakes.
That's correct and some are adjustable. On those units it is
necessary to balance the system after changing out the master
cylinder.

But aren't the front and rear independent systems, with separate reservoirs
and all? It sounds like this valve is a single point of failure common to
both systems.

Most cars have two independent systems,
right front/left rear and left front/right rear.