[T2] Vacuum assist

[Bob Pratt]

The bus 1971. According to Bentley, the adjustment is on the front side of the vacuum assist as it doesn't have the short adjustment rod like the pre-1972 busses have.

 I disconnected the brake pedal from the shaft that goes into the front of the vacuum assist and there was no movement of the pedal. 

I also noticed that the vacuum hose from the vacuum assist filter had no clamp on it wand was just sitting on the connection. I put a clamp on it, but it made no difference.

I should be getting the vacuum check valve on September 5th.

Bob Pratt

> On Aug 30, 2015, at 3:51 PM, Jamie <jrivers at globalserve.net> wrote:
> 
> 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
>