[ROVERNET - UK] P6 Vacuum servo ???s

Steven Dibdin sdibdin at hotmail.com
Mon Mar 17 02:15:43 GMT 2008

Hi Patrick,

Is this on a 2000 or a 3500? I had the 'pleasure of repairing both servos on 
my NADA 2000TC a two years ago.

On the 2000 TC the air valve is opened by small psiton in the servo cylinder 
body (it's the one that sticks up at 45 degrees to the main part of the 
servo cylinder). When that opens it allows atmospheric pressure on one side 
of the big diaphram you saw in the main vacuum chamber when you took it 
apart. When you have a vacuum (from the inlet manifold) on the side of the 
diaphram by the cylinder and atmospheric pressure on the other side it will 
push the main piston forwards. This basically adds the pressure from the 
diaphram to your foot pressure in the hydrolic system. Sounds more 
complicated than it is really.

Answers to your questions:
[1] No, the valve should have been open. Sounds like someone forgot or the 
servo kept jamming on the brakes. This can happen if the small air valve 
operating piston is stuck or stiff in operation. One of my servos had been 
disconected from the vacuum line for that reason when I got the car.

[2] Keep asking questions here, what this lot don;t know on this sort of 
thing isn't worth knowing. Also check ebay for a factory manual, it's pretty 
clear and has fantastic drawings of this and other systems.

Hope this helps,


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