NCZZZ Posted October 24, 2009 Share Posted October 24, 2009 1971 240 push rod dilemma. I put on a new brake master & vacuum booster. I have almost no pedal. I bled the master cylinder initially and once again when it was on the car--was getting no air bubbles. Bled all other lines. Fluid was pushed through OK when bleeding, though it was not forceful. I verified that the reaction disc is in place in the booster. My question about the push rod is the adjustment. The factory service manual states as follows: "Upon completion of the assembly, adjust push rod end height so that depth from the flange surface to the push rod end is 3.5 - 4 mm." Go figure, I did not pay attention before I took the old core back -- it is long gone. Is this adjustment measured with the push rod end adjusted towards the inside or outside of the flange mounting surface? I took the word "depth" in the manual to mean the push rod would be measured from the end to the flange surface from inside the booster. Is it possible I have the push rod adjusted the wrong way? Any input would be greatly appreciated! Quote Link to comment Share on other sites More sharing options...
Miles Posted October 24, 2009 Share Posted October 24, 2009 Per the Haynes manual it is 3.5mm - 4mm from the face of the mounting flange. Turn the adjuster out until the tip of the push rod is 3.5mm - 4mm from the face of the flange. Don't extend the push rod adjustment out too far or you will lock your brakes up. The MC piston has to return far enough to allow fluid in the MC to drain out through a relief port inside the MC. Long story, but there are threads on this issue in the brake section. If you should lock your brakes up by over extending the push rod simply open the bleed screws on the MC with a 10mm wrench to relieve the pressure and limp home. And then back off the rod adjustment in small increments until no more lock up. Miles Quote Link to comment Share on other sites More sharing options...
NCZZZ Posted October 24, 2009 Author Share Posted October 24, 2009 Thanks, Miles. Sounds like I probably did adjust in the wrong direction. Guess I'll be disassembling. For some reason the word "depth" in the FSM description got me turned around. The Haynes description does sound like the rod end would be out in front of the flange instead of inside. I'll post tomorrow if that is the case. If some other dumb schmuck happens to read the manual the way I did, here it is... I've been over every inch of this car over the lat 15 months...I think I am almost at "burn out". I'm ready to drive this thing. It is 99% except for the brake issue. Later... Quote Link to comment Share on other sites More sharing options...
Miles Posted October 24, 2009 Share Posted October 24, 2009 (edited) Another tip on adjusting the push rod. You don't have to remove the MC to adjust the push rod. There is enough flex in the hard pipes that connect to the MC that you can just remove the nuts from the MC mount, pull it forward and gently push it aside to allow access to the push rod adjustment. When I swaped in a 280ZX MC into my 72 240Z I used this technique to fine tune the length of the push rod. There is also an adjustment on the break pedel under the dash you can adjust to get less or more pedel throw. Miles Edited October 24, 2009 by Miles spelling 1 Quote Link to comment Share on other sites More sharing options...
NCZZZ Posted October 27, 2009 Author Share Posted October 27, 2009 Well, I readjusted the vac booster push rod to 3-4 mm past the face of the mount flange towards the master cylinder. Afterwards, with the car off, pedal was solid (as it should be). Started the car up and felt the pedal soften (as it should). Took a couple of test drives around the neighborhood and sure enough after each one the brake were now dragging to the point of lock. Starting adjusting the rod back. Seemed OK. Took the car out for a pretty decent run and had to stop 4 times and readjust. When it was all said and done, the push rod is essentially back to where I started. I am certainly no expert, I just don't get it (well, I did get it straight anyway). The car was started before and had vacuum but I had no pedal at the original adjustment per the FSM. Can anyone explain? In conclusion, it appears the FSM description of adjusting the rod to a depth of 3-4 mm from the face of the mounting flange was correct. They sure did not tell you you would have to start from the other end and then adjust back to it. Hope this helps someone else out there. Quote Link to comment Share on other sites More sharing options...
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