[Mgs] B master cylinder

[Paul Hunt]

A brake master consists of a cylinder and a piston.  The cylinder has two 
ports in it - an inlet port that is only open when the piston is fully 
released which lets fluid from the reservoir fill the cylinder, and an 
outlet port that is 'open' all the time and is what the piston pushes fluid 
out of to operate the brakes.  As soon as the piston starts to move the 
inlet port is closed off by the piston so all the pressure is applied to the 
outlet port.  So if no fluid is coming out of the outlet either it is 
blocked, or the inlet port is blocked and not letting any fluid into the 
cylinder.  Obviously the dual circuit with pressure differential switch is 
more complicated, but I'd expect that with dismantling you should be able to 
access and check both ports for each circuit.  From Haynes the rear section 
seems to feed the front brakes and the front section the rears, and the two 
pistons are not physically connected except by fluid, so it seems possible 
that the front section could be empty of fluid i.e. its inlet port is not 
allowing fluid in.  I take it there is enough fluid in the reservoir to fill 
both sections?

PaulH.

----- Original Message ----- 
> In trying to bleed my 79 B's brakes, I found nothing was happening at
> the rear brakes.  I checked each connection back toward the master
> cylinder and found the same thing.  Finally, I disconnected the line
> from the master cylinder and found that no fluid comes out of that
> port on the master cylinder.