This may help us all to understand how a servo works. If anyone knows how to import the diagram direct into the form I'd appreciate the tip, rather than posting just the short cut.
http://auto.howstuffworks.com/auto-p...wer-brake2.htm
If you click on the pedal, it shows the valve at the rear opening to allow atmospheric pressure against the back of the diaphragm, whilsyt there is a vacuum on the front, creating the assitance to the pedal pressure.
As the pressure on the pedal is released, the valve at the rear closes and allows the vacuum to reform at the rear of the diaphragm, equalising the pressure on both faces, and allowing the pressure on the master cylinder to be released.
There should be a small amount of movement in the pedal from its rest position to allow this valve to open, before it meets with pressure from the diaphragm plunger and starts to apply pressure to the master cylinder.
The message appears to be do not try to take out the slack movement between the pedal at rest and the servo. ie do not set the brake switch too close to the pedal to prevent it coming back as far as it is intended.
Quote:
Originally Posted by Grey V8 Pete
Slightly off topic but, when I first apply the brakes after starting the engine there is a noticable “clonk” from the dual servo. This only happens the once and does not recur until after the engine is next started. All mounting bolts, clevis and pedal bolt have been checked and are secure. The servo operation remains the same and braking efficiency remains the same i.e. brilliant! 
As a theory: The diaphragms seem to be on two in-line but physically separate push rods. I guessed this from the fact that before fitting the unit I could move the primary push rod sideways (when fitting the clevis over the fixed pedal bolt) which would not be possible if the rod was attached to both diaphragms. I wonder if there is more residual vacuum in one sevo chamber than the other so that as soon as the engine starts and supplies more vacuum, pressing the pedal makes one of the diaphragms respond a little faster than the other to take up the slack. Has anyone else noticed the same? Peter. |