Miles Posted July 23, 2004 Share Posted July 23, 2004 I have completetly rebuilt my 72 240Z brakes over the last year. All parts are new and stock except for the hard lines. The MC is US built and installed three weeks ago. The MC was bench bled, bled on the car and all four corners have been bled using standard bleeding procdures and then using a power bleeder. The problem is I can not get a firm pedal with minimum travel before brakes start kicking in. The pedal doesn't seem to sink past a certain point and pumping doesn't improve the firmness. I just replaced the vacume booster and adjusted the push rod that goes into the MC cylinder. As measured from face of the spacer on the booster the length of the push rod is 9 mm. The depth of the stock 7/8 in. MC cylinder as measured from the face of the mounting flange is 10 mm leaving 1 mm space between the end of the push rod and the bottom of the hole it goes into. Still the pedal travels a good 2 inches before noticable braking action. While the brakes stop the car it takes increasing pressure to really get the car to slow down. I know there is something wrong because at one time the pedal was firm with a 1/4 in. of free travel and the brakes would put you up against the seat belt with just normal pedal pressure. It almost seems like the fronts are doing all of the braking. Should I increase the length of the push rod? From searching old posts this is a common complaint for both stock brakes and brake upgrades. I am about to rip out the stock stuff and do the complete vented rotor, 15/16 in. MC and rear disks. By contrast, I rebuilt the stock brakes on my son's V8 72 240Z almost two years ago. The brakes work well and I have not had to do anything to them since. Any help is appreaciated. Miles Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 23, 2004 Share Posted July 23, 2004 Sounds like another reaction disk problem to me. See below: http://hybridz.org/nuke/index.php?name=PNphpBB2&file=viewtopic&t=34709&highlight=reaction+disk Quote Link to comment Share on other sites More sharing options...
Miles Posted July 23, 2004 Author Share Posted July 23, 2004 It does sound like a reaction disk problem, but I just installed a rebuilt power booster last week. How can you tell if the reaction disk has fallen out? There is a seal around the push rod. Does that seal pop out? Miles Quote Link to comment Share on other sites More sharing options...
Guest Chez Roban69 Posted December 9, 2004 Share Posted December 9, 2004 I'm having the same issue - and the shortcut doesn't work. This thread could REALLY help me out... Searched "reaction disk" and got nothing specific and way too much to handle w/ my dial-up connection. Help. John can you try shortcut again? Or clue me in on how to yield narrower results on a search? Thanks, Robin Quote Link to comment Share on other sites More sharing options...
Miles Posted December 11, 2004 Author Share Posted December 11, 2004 Robin What kind of problems are you having? I ended up buying a max vac from Autozone for my 72 240Z. I checked to see if there was a reaction disk in the new max vac. There wasn't. But the place were the reaction disk sits was also redesigned and different then my stock unit. Evidently the reaction disk was designed out of the replacement. Which was good news since I was always a bit afraid to adjust the push rod that engages the MC fearing that I might drop the reaction disk. With a stock MC my brakes improved somewhat, but they were still not firm. I suspected that my MC might be leaking internally so I replaced the stock MC with the larger bore MC from a 79 280ZX. The 280ZX MC was also cheaper. I carefully bench bled the new MC by hooking old rear brake bridge tubes with clear plastic tubes pushed onto them from the outlets on the bottom of the MC. I connected clear plastic tubes from the bleed screws and then bent all four plastic tubes so they returned fluid back into the proper reservoirs. The plastic tubes were held in the reservoirs with clothes pins. You can just take one old rear bridge tube and cut it in half and then fit 1/4 in. clear plastic tubing over the cut ends. Make sure there are no leaks in your connections. I took my time and pushed in the MC piston slowly watching the bubbles get smaller in the clear plastic tubing as I continued pushing the piston in. I had to close the bleeder screws after each pump at first because bubbles would get sucked back into the plastic tubes initially. I let the MC sit for about ten minutes and then pumped more very fine bubbles into the reservoirs. When I was ready to onstall the MC in the car I closed the bleeder screws and plugged the outlets with rubber stoppers I bought for that purpose from the hardware store. I left the stoppers in until I was absolutely ready to hook up the hard pipes so as to minimize fluid leaking out of the MC. I then bled the brakes using a power bleeder ( messy, but effective). The brakes were firm, but there was still too much pedal travel so I pulled the MC loose from the max vac while leaving the brake lines attached. (Just push the MC and the connected lines away from the max vac.) Then I adjusted the push rod out and tested the pedal feel while driving and then repeated the push rod adjustment 2 or 3 more times. Be careful not to adjust the rod out too far as it can cause the brakes to lock up. With the the new max vac, new large bore 79 280 Zx MC, proper bleeding and push rod adjustment I now have very firm brakes. They are not great, but better then my old stock brakes. One factor in going to the larger bore MC is that I plan on installing large vented rotors and Toyota calipers soon. The larger MC did improve my brakes and gives a firmer pedal then my stock MC. With the larger bore MC you do have to apply a little more pedal pressure due to the change in bore size. Miles Quote Link to comment Share on other sites More sharing options...
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