[T2] Vacuum assist

[Jamie]

i dunno.. the way I understand the valves in the braking system,, the port 
valve inside the booster causes the diaphram to assist the movement of the 
application rod
once you cover that port ,, the vac removes the air on one side of the 
diaphram ,, and allows atmospheric pressure to assist in applying the 
movement to the brake pedal

so,, if the master cyl wasn't installed with the correct clearance,, and it 
is already in a state of application.. it will be difficult to impossible to 
bleed,, and it may cover that port valve already,, so as soon as the vac is 
applied,, the pedal will move toward brake application.

OR
if the old master cyl leaked fluid into the booster,, there will be fluid in 
the booster...
once there is enough fluid,, that fluid covers the port valve ,, the vac 
starts to be unequal on each side of the diaphram , and atm pushes the pedal 
toward the master .. applying the brakes and it will appear all on its own.. 
if you turn off the vac [engine] the spring in the booster will return the 
brake pedal to normal position

the check valve holds vac in the booster while there is little or no vac 
coming from the engine,, during open throttle situation ,, the check valve 
doesn't apply the brakes, it will allow equal vac on both sides of the 
booster diaphram.. ... or if installed wrong.. no vac to the booster ..  or 
if it isn't present or malfunctions so it breathes both ways.. you will have 
vac avail at closed throttle and not at open throttle... but the pedal will 
not move until the port inside the booster is covered.

the port valve inside the booster will apply the brakes if it gets covered.. 
and it normally gets covered with the application of the brake pedal... but 
it can appear to be covered by the booster being full of fluid.

the booster can be a bugger to drain in place..


----- Original Message ----- 
> Jamie -
>
> I believe Bob indicated in his original post that he had replaced the
> master cylinder.  Sounds like 1-way check valve in the engine compartment
> to me, at least that's been my experience.
> On Sun, Aug 30, 2015 at 9:31 AM, Jamie <jrivers at globalserve.net> wrote:
> <SNIP>
>> old master cyl can leak out the seal that is between the master and the
>> booster,, and you will have a fluid leak that you can't see..
>> Jamie