clayton 260Z Posted August 31, 2007 Share Posted August 31, 2007 Heres the problem.. I HAVE PLENTY OF BRAKE PEDAL ITS VERY FIRM BUT NO BRAKING POWER, I HAVE REPLACED, BRAKE BOOSTER, MASTER CYLNDER, CHANGED TO TOYOTA CALIPERS CROSS DRILLED ROTORS UP FRONT, MAXIMA CALAPERS IN THE REAR. I HAVE WHAT I WOULD BEST DESCRIBE AS NO BRAKING POWER, IT SEEMS THEY DO NOT WANT TO GRAB. I CAN NOT EVEN LOCK THEM UP UNDER FULL PEDAL. I DO NOT LOOSE PEDAL UNDER BRAKING. THE CAR WILL STOP BUT WITH LITTLE CONFIDENCE. ANY SUGGESTION? Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted August 31, 2007 Share Posted August 31, 2007 Pump the pedal about 5 times with the engine off, then holding your foot on the pedal, start the engine. The pedal should fall a couple inches when the engine is started and pulls a vacuum on the booster. If the pedal doesn't drop, your booster isn't working. Could be a booster issue or it could be simply lack of engine vacuum. You need at least 18"/hg of vacuum for the booster to function properly. If you don't have that much, the pedal may drop when you start the engine, but it won't provide enough assist to be effective. Edit: and turn your caps lock off. Quote Link to comment Share on other sites More sharing options...
e_racer1999 Posted August 31, 2007 Share Posted August 31, 2007 ^ya, since i installed a hot cam, i have to have the choke on to get reliable braking power. try braking with the revs up. Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted August 31, 2007 Share Posted August 31, 2007 I'm using a vacuum pump from a mid '80s chevy celebrity....they are mounted right below the battery tray with Torx bolts. The automatically turn on at 15"/hg and shut off at 23"/hg. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted August 31, 2007 Share Posted August 31, 2007 I would suspect the booster. You could remove the vacuum line (then plug the line going to the motor) from the booster, and if nothing changes, then I'd focus my attention on it. Quote Link to comment Share on other sites More sharing options...
e_racer1999 Posted August 31, 2007 Share Posted August 31, 2007 I'm using a vacuum pump from a mid '80s chevy celebrity....they are mounted right below the battery tray with Torx bolts. The automatically turn on at 15"/hg and shut off at 23"/hg. i was wondering if such a creature existed! thanks for confirming it and giving me a new project Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted August 31, 2007 Share Posted August 31, 2007 I would suspect the booster. You could remove the vacuum line (then plug the line going to the motor) from the booster, and if nothing changes, then I'd focus my attention on it. All that will confirm is that the booster is not working, not why its not working. Another thing you can do is pull another car up next to it and run a hose from the other manifold to the booster on your Z...then try the brake pedal. The proper way to diagnose it would be get a vacuum gauge and confirm at least 18"/hg at the booster vacuum hose. If there is not 18"/hg of vacuum, fix that first, then go from there. Quote Link to comment Share on other sites More sharing options...
clayton 260Z Posted August 31, 2007 Author Share Posted August 31, 2007 As It Stands I Have +18"/hg Vacuum And Have A Very Strong Pedal With No Fade It's Hard To Describe But Again It Seems That The Calipers Aer Not Grabbing The Rotors. This Thing Should Stop On A Dime. I Have Bleed The Brakes Checked For Leaks (none ) They Work But Are Weak. Will Check Everything Again And Many Thanks For Your Help.... ..frustrated... Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted September 1, 2007 Share Posted September 1, 2007 I am gonna jump on here and post as well. I have precisely the same problem, so I know how the OP feels. I have new MC, new booster, new pads and rotors up front, new stainless brake lines and speed bleeders all the way around. The brake pedal is nice and hard, but it requires a LOT of pressure to get it to stop. I can stand on them and they will start to lock up the front, so I know it's working semi-closely. I went to my local autozone in desperation to see what they said. One guy said that maybe I still have an air pocket between the MC and the lines (from installing it), but I doubt that since the pedal is hard and doesn't move much at all. They said (and this is where the OP and I MAY have the same problem) that there could be dirt in the lines causing them to do this. I have a hard time believing that, though, since it doesn't pull to one side or anything. Any guru's out there have any ideas? What will the car do with the checkvalve on backwards? You should be able to blow through it from the booster side, no? Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted September 1, 2007 Share Posted September 1, 2007 i was wondering if such a creature existed! thanks for confirming it and giving me a new project Lotsa old skool nasty domestics use them. Some are belt driven and some electric. Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted September 1, 2007 Share Posted September 1, 2007 Have either of you 2 with the hard pedal problem checked for booster function using the method I described in my first post? Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted September 1, 2007 Share Posted September 1, 2007 Have either of you 2 with the hard pedal problem checked for booster function using the method I described in my first post? Yes, I did. I figured my problem. The check valve had been installed backwards. I guess when the old (broken) booster was being stupid we were trying to figure what it could possibly be and ended up leavin it in backwards. They work now although they feel like I don't have stainless lines. I probably just have to bleed it again. Quote Link to comment Share on other sites More sharing options...
clayton 260Z Posted September 7, 2007 Author Share Posted September 7, 2007 Well went back and reworked brake system, and found that I had a booster problem replace it and everything is now in great working order. Thanks for the help...... Quote Link to comment Share on other sites More sharing options...
z-ya Posted September 9, 2007 Share Posted September 9, 2007 Do you have the stock 7/8" MC or a 15/16" one? Quote Link to comment Share on other sites More sharing options...
S30TRBO Posted September 11, 2007 Share Posted September 11, 2007 On my 240Z I just did a similar upgrade. ~Toyota 4-Runner Calipers ~240SX Rear Calipers ~'79 ZX Master I re bent the brake master lines to allow the ZX master to work. A side note: on the 240Z the front reservoir is for the front brakes and the rear is for the rear drum brakes. On the ZX they are reversed front is rear and rear is front. When upgrading to rear calipers first take the guts out of the proportioning valve in the rear as it is setup for drum brakes. Break brake lines loose, take mounting bolt out and bring to work bench much easier. Put in vise, remove bolt on the bottom, remove the c-clip and pull the small valve out, reinstall the bolt. This allows more fluid to flow for the rear disc brakes. I upgraded to the '72 or later brake booster since the rod is longer than my '70. The early booster has a shorter rod and won’t push the plunger in the master all the way. You need hog out the pedal clip for it to fit and the pin to slide back into place. With the brake upgrades minus changing out the booster I had no pedal. I had minimal in the front and no rear brakes. All is very well now. Hope this helps. Quote Link to comment Share on other sites More sharing options...
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