No vacuum ?

[Stevejaguar]

Series 1 2+2
New master cylinder, new servo.
Bled brakes and a good pedal. However. If I press the pedal then start the engine the pedal doesn't go down slightly.
With the engine off I cannot hear the servo working off the vac cylinder for 2-3 presses.
Master cylinder or servo problem?
How do I test the 3 way vac valve ?
Any thoughts?
Steve

[mgcjag]

Hi Steve there are very detailed drawings and explenation of the brake system operation in the service manual..vacume and fluid flow etc.......you can test the 3 way by just blow/suck through it.....also check out the Reaction/air valve on the end of the master.......is the small piston in the end of the master operating the valve.....Steve

[politeperson]

You might have your pipes on the servo connected the wrong way around.

The rear servo pipe should turn from vacuum to atmospheric pressure when the pedal is pressed.

Pull off the rear servo vacuum pipe and have an experiment with the engine running.

[Stevejaguar]

Hi and thanks for the replies.
After 24 years of owning my 2+2 the pages with the brake system on are well thumbed, second only to the section on carburettors.
All the pipes are connected correctly and the vacuum to the rear of the servo changes to atmospheric when the brake pedal is pressed.
The puzzling thing is still that if I press the brake pedal then start the engine, the pedal doesn't go down slightly as it used to. With the engine switched off and pressing the pedal I used to hear about 3 movements of the servo before the vacuum in the tank was exhausted. That's not there anymore.
Any thoughts?

I cant take the car out for a test as there are no doors on at present .
Steve

[mgcjag]

Hi Steve.....so are you getting vacume when you start the engine to the servo....valve problem?...blocked/collapsed hose......hole in vac tank (not sure what symptomes you get).....Steve

[Stevejaguar]

Hi , yes when the engine is running I have vacuum to both sides of the servo. When the brake pedal is pressed the vacuum is lost from the rear portion of the servo.
Steve

[mgcjag]

So is there vacume in the vac tank......possible valve issue

[politeperson]

Maybe it is working perfectly?

[Stevejaguar]

I have vacuum in all the right places. There are no leaks and the check valve is working as it should.
When I depress the pedal with the engine running the rear section of the servo changes from vacuum to atmospheric.
So all seems good.

I wonder why when I depress the pedal and start the engine the pedal does not go down slightly as it used to.
Also the servo does not seem to exhaust itself with the engine switched off when pressing the pedal 2 or 3 times as it used to.
I cannot road test the car at present but would like to be happy with the brakes until I can test it whilst I get on with all the other jobs that need doing in the meantime.
Steve