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Brake booster push rod adjustment


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from what i see on youtube i am supposed to turn the little nut on the end to extend it out (its not long enough). Can someone confirm this is correct. I put vice grips on it and the wrench wont budge it....it could be its frozen up, just nervous to put too much force. I have broken things previously doing that 🙂


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  • 2 years later...

So, I'm nearing completion on my 73 restoration and I'm having problems with the brakes.  They just don't feel right and when applied will not lock up the wheels.  I'm not running the engine but they hydraulic action should work with or without the booster having vacuum on it, otherwise you wouldn't be able to stop the car if the master vac failed.  I've been working on brakes for more than 50 years and have never seen a system where the brakes would fail if the power booster failed.  There's not that many components in this brake circuit so I can't believe I'm having this many problems. Searched the forum and though I may have found the issue being the reaction disc.  So here's what I've done so far:  all new brake lines, new master cylinder, rebuilt proportion valve, rebuilt brake light switch, adjusted pedal height, bled entire system numerous times.  No leaks anywhere and flow out the bleeder plugs on each wheel. The proportion valve is on the fire wall not at the rear brakes. Retested master cylinder to be sure it was not defective.  It is not. Disassembled the master vac to check the reaction disc.  It was in the proper position.  Cleaned it up and glued it on just to avoid future problems.  While I had it apart, I freed up the threaded end of the push rod using the thermal wrench (that was a real nail biter}. I'm kind of leaning towards insufficient travel of the master cylinder piston. Looking at the pic posted by Zed Head I need to know what dimension "B" is.  I'm not sure which FSM the pic came from, but I checked 71-72 & 73 FSMs and cannot find that pic or the dimension.  My 73 fsm says 3.5-4.0 mm from flange surface (which I assume is the front surface of the spaces that goes between the master vac and master cylinder) to the end of the pushrod. Well even with the pushrod end screwed all the way in, it sticks out more than 4mm, more like 8-10mm. So if anyone knows what the "B" dimension should be, let me know.  I'm thinking with the problem I'm having, more stick out of the pushrod would be better. I'm considering backing the pushrod all the way out until it touches the master cylinder piston, then turning it in an 1/8" or so.  Any thoughts suggestions or other things I should be checking?????

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Yea, that's the same pic I have, but like I said even with the end screwed all the way in it still sticks out mor than 4 mm. Do you think my logic makes sense that more extension on the pushrod would help my problem?.  I just get the feeling the master cylinder piston is not being pushed far enough forward to lock up the wheels.

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What does the brake pedal do?  The play in all of the mechanical parts gets taken up when you press the pedal.

There's a tool for adjusting the master vac.  But getting it properly adjusted probably won't make the brakes work differently with no vacuum.


If it's the rear wheels that won't lock up it might just be poor quality shoes.  I found when I replaced mine that the shoes seemed to be designed for oversize drums.  They only contacted on the ends.  I couldn't lock up my rear wheels at all and the parking brake was definitely not an emergency brake.





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