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How much throw to fully engage master cylinder

peakandscoot

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I am changing my single reservoir to a dual reservoir with dual brake booster and there are 3 different rods to chose from that mount to the pedal. The shortest one seems to fit the best but im concerned that i am fully engaging the master cylinder. The engine is not in so i cant play with it. I can measure the travel distance of the rod coming out of the booster before i attach the master cylinder. It looks like im a little over an inch but if i depress the master by hand it seems like i can depress it closer to an inch and a half. Should i change to the longer rod which would bring my pedal further off the floor, should i be able to move the rod the full distance.
 
What I have done in the past for this is to put a dab from a grease pencil on the end of the booster pushrod and it enters the master cylinder. Then you can pick the right one and adjust the end so that it basically just touches the inside of the master cylinder shaft hole when the master cylinder is bolted to the booster. I viewed that as my rough adjustment.

Now...a couple of other things...what I wrote above should work just fine. It is possible that given different brands of master cylinders some might still have a little bit of play even with the push rod touching when in a neutral state. In that case, a bit of trial and error works. Too much engagement and the brakes could drag a bit which is of course undesirable. The alternative of too little is simply too much pedal travel to get good braking action which will hurt your reaction time in a crisis...again, I simply just play with it once the car is running, getting the rod to be a little tighter from trial and error (little is the key word, the adjustment is like half a turn).
 
Gap should be .020" and tool to measure it.

booster_gap.JPG Booster pushrod_adjust_tool.gif
 
Choose the length of rod to get the pedal at the correct height from the toe board to be comfortable and give you enough movement to stroke the master cylinder.
Do not worry about burying the master right at the end you just want enough movement to move the secondary piston which will allow you to bleed the brakes correctly and apply pressure to both circuits of the master.
In my opinion I set the clearance at zero to 0.004"
The pedal has to move a relatively long was to move that push rod 20 thou.
You run the risk of ending up with a low pedal before the brakes start operating.
 
Make sure you have a gap. Keep the gap as small as possible, but MAKE SURE there is a gap. If you have none or, in other words, the rod is always applying pressure, your M/C wont function right and will fail on you.

follow the measurements given above
 
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