Dual brake systems work like two singles, with two differences.
First, there are two pistons in the master, not one, Each operating a
circuit.
Two, the pistons aren't connected firmly to each other. The rear circuit's
piston is operated by the front circuit's piston. There is a spring between
them that controls (at least partially) the pressure differential between
the circuits.
If one circuit is bad, the pedal will be lower and more pressure will be
required to stop the car.
Possibilities are: air in line, blocked line, or a defective master.
When you rebuild a dual circuit master, both cup seals have to go on the
pistons in the same direction. It sounds simple, but is a common mistake.
Doing this will allow fluid to be pumped out of both circuits only when
there is no resistance as when the line is disconnected.
Another possibility is that one of the ports is blocked.
When you disconnect a line and press the pedal, fluid should literally shoot
out. If it doesn't, there is either a problem with the master or you have
lots of air in it. If you haven't bench bled the master, you can still do
it in the car. Get plastic fittings that go into the master where the lines
attach. There will be plastic hoses that attach to the fittings. .Place
the other end of the hoses into the reservoir. Pump slowly, and all the way
down until there are no more air bubbles. Attach the line and bleed
normally.
If there is still no fluid to the rear, bleed at every union.You will find
where the blockage is.
|