Z24O Posted June 13, 2006 Share Posted June 13, 2006 hi guys, just finished a search with no luck i have just upgraded my front brakes to larger calipers and ventilated discs so as suggested i fitted the larger 15/16 master cylinder off a 280zx(rebuilt) i bench bled the master cylinder before installing it then bled up the brakes the pedal seemed reasonable-resistance from 1/4 to 1/2 on depressing-however upon starting the engine the pedal went from go to whoa without any hint of resistance i checked that fluid was still being pushed through the calipers and it was with no apparent air anyone got any ideas as to what the problem could be?? paul ps i checked the rod depth into the master cylinder by measurement and it seemed ok Quote Link to comment Share on other sites More sharing options...
mark Posted June 13, 2006 Share Posted June 13, 2006 What's on the rear? Quote Link to comment Share on other sites More sharing options...
alexideways Posted June 13, 2006 Share Posted June 13, 2006 I heard that there are 2 different master cyl. models for the ZX and only one will work, check it out, I think they have both pictures in: BRAKES FAQ http://forums.hybridz.org/showthread.php?t=103767 Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted June 13, 2006 Share Posted June 13, 2006 is it possible that the one way vacuum valve [installed inline with the vacuum line from the intake manifold to the vacuum booster-vacuum must flow from intake to booster] is either missing or installed backwards? Quote Link to comment Share on other sites More sharing options...
Z24O Posted June 13, 2006 Author Share Posted June 13, 2006 is it possible that the one way vacuum valve [installed inline with the vacuum line from the intake manifold to the vacuum booster-vacuum must flow from intake to booster'] is either missing or installed backwards? thanks guys booster worked fine before have drums on rear have right m/c Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted June 13, 2006 Share Posted June 13, 2006 You shouldn't need the larger master with rear drum brakes. Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted June 13, 2006 Share Posted June 13, 2006 check for leaks everywhere very closely. Make sure the calipers are installed such that the bleed screws are pointed up. Quote Link to comment Share on other sites More sharing options...
Z24O Posted June 13, 2006 Author Share Posted June 13, 2006 check for leaks everywhere very closely.Make sure the calipers are installed such that the bleed screws are pointed up. thanks guys bleed screws upwards 240z m/c was too small(not enough volume of fluid to operate the calipers) as the pedal was dangerously close to the floor with new pads...would run out of travel when pads wore....i know this for a fact as it happened on another like conversion(these twin pot calipers are off a 4000lb car operating 330mm discs) the main question or clue is why is there resistance on the pedal until the engine is started(vacuum assisted) Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 13, 2006 Share Posted June 13, 2006 I am guessing the booster has something wrong with it. Do the brakes actually work with the engine off? Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted June 13, 2006 Share Posted June 13, 2006 Do the brakes work with the engine running, but the peddle is just a little lower? As long as the peddle doesn't hit the floor, this is normal. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 13, 2006 Share Posted June 13, 2006 Did you check the reaction disk? Similar threads in the past have been posted due to the reaction disk falling out and into the booster. Very common issue when swapping masters. Quote Link to comment Share on other sites More sharing options...
bjhines Posted June 13, 2006 Share Posted June 13, 2006 more information.... Do the brakes STOP the car.... engine running or not... If you have not pushed it and stoped it with the new set up then you have not finished the job... Make sure the rear drums are installed and adjusted with wheels on and lugs tight... rears have little clickers that are activated by the hand brake lever... keep pulling until they stop clicking... reassemble the front brakes with pads and pins... press the pedal hard a few times.... It should not budge beyond half way with your *** hovering from pressing the pedal hard... if it goes beyond this then you still have air in your lines.... you can bench bleed them before hand... but if the resivoirs ever emptied between the bench and the finished installation you wasted your time. If you are a wimp.. or you dont want to cave in your rusty firewall then run the engine and press almost as hard.... 150LBS of pressure on the pedal at least... if the pedal moves more than half way then you have air in your lines... BTW... the pedal should actually support your weight for an extended period of time... it should not sink gradually... I have vented rotors with the S12W calipers and rear drums... I am using the original 240Z master... I run the car on track... the brakes work without problems under extreme conditions... I also flush the entire sytem regularly... Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted June 13, 2006 Share Posted June 13, 2006 240z m/c was too small(not enough volume of fluid to operate the calipers) as the pedal was dangerously close to the floor with new pads...would run out of travel when pads wore.... The stock MC may have been too small, I don't know. But you do realize having worn brake pads should have no impact on pedal travel. As the pads wear more fluid should fill the calipers resulting in the same pedal movement for the same brake movement. There is an adjustable push rod between the back of the MC and the booster that needs to be lengthened when swapping the MC. Or you could have the reaction disk problem Jon talks about. Or maybe there is air in the lines. Quote Link to comment Share on other sites More sharing options...
skipzoomie Posted June 13, 2006 Share Posted June 13, 2006 REACTION DISC.......................Very common problem. Quote Link to comment Share on other sites More sharing options...
Z24O Posted June 15, 2006 Author Share Posted June 15, 2006 thanks guys in answer to recent posts.......... checked the sticky's before this upgrade,the actuator rod in the booster was not disturbed so i don't think the disc is the cause nor the booster when bleeding the calipers i am not getting any air in the line and that is after the car sat over night,i would expect ANY air to have risen to the bleed nipples feel uneasy about seeing if the brakes stop the car when the pedal goes straight to the floor without resistance with the motor running....i figure this is about as close as you get to confirming you have no brakes without actually running into a pole booster worked fine before,i think this is barking up the wrong tree,i may be wrong? what would cause a hard 1/2 pedal and then NO pedal with vacuum assist??? Quote Link to comment Share on other sites More sharing options...
bjhines Posted June 15, 2006 Share Posted June 15, 2006 nothing unususal... It simply will not move all the way to the floor under ANY circumstances (Booster or hydraulic ram or Hercules) unless... the seals are blown, there is a leak, there is air in the line, you have a broken/loose caliper, the pedal box/firewall is broken or the rear brake parts are not assembled... that is it... and I still don't think it will move all the way to the floor even if half the system is nonexistant.. front or rear... Your booster works fine... forget about the fact that it easily moves the pedal most of it's stroke... it is working... the hydraulic system is to blame... all those valves and tees and switch and gack in the system can and will eventually fail... but none of it will allow the pedal to go to the floor without leaking fluid out of the system... look for leaks... check that all parts are assembled in such a way that it LOOKS like it will apply the pads to the friction surfaces... How much fluid did you put through the system when bleeding?... you can waste a lot more fluid bleeding than the system actually holds... I never wait any amount of time when bleeding a dry system.. a little air pressure to force fluid into the master cyl while pumping the pedal is all it takes to get things going... I push hard and fast on the apply stroke.. and I release very slowly to allow fluid to enter the system(3-4 secs)... I try to repeat the strokes as quickly as possible to keep air moving through the system... I use a hose attached to the bleed nipple (thread sealant on nipple threads)... I run the hose into a bottle and keep it submerged... this keeps air from re-entering the calipers when you release the pedal.... works every time... I have YOUR system but with the smaller 240Z master cyl.... ohh and remember to bleed 1. driver rear 2. passenger rear 3. passenger front 4. driver front rinse and repeat.... Quote Link to comment Share on other sites More sharing options...
Z24O Posted June 15, 2006 Author Share Posted June 15, 2006 thanks guys update definately no leaks of brake fluid i have been concentrating on re-bleeding the front brakes as i primed the m/c before fitting and the rear brakes were ok before the pedal stays hard at the 1/2 way point if you keep pressure on it with the engine off....turn it on and it goes straight down with no effort at all....revs rise slightly on pumping brake pedal indicating vacuum being drawn i can't help thinking it's to do with the actuator rod,even though i measured the static depth in the m/c and it was within a bees privates......lets say the rod was too long or too short-what symptoms would i see???? thanks for your patience paul Quote Link to comment Share on other sites More sharing options...
bjhines Posted June 15, 2006 Share Posted June 15, 2006 Don't just concentrate on the front brakes when bleeding... do them IN ORDER(front and rear).. and repeat bleeding IN ORDER...you say the pedal is "hard" with the engine off.... well my panis get's "hard" too... but not as hard as diamond...It is relative... If the pedal can move all the way to the floor... under any circumstances.. there is a problem with the hydraulic part of the system... You may "think" that the pedal is hard without the booster helping... but if you push with your weight behind it I garantee it WILL move all the way to the floor with or without the engine on... don't get hung up on the booster and rod settings until you have gotten the hydraulic part of the system truely "HARD"... not just "dickhard"... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 15, 2006 Share Posted June 15, 2006 Sure sounds like the reaction disk to me. Takes less time to check the disk then it does to bleed the brakes. Quote Link to comment Share on other sites More sharing options...
bjhines Posted June 15, 2006 Share Posted June 15, 2006 I agree that the reaction disk can make pedal ""feel"" inconsistant through the stroke... if that is truely what he is describing... but the fact that he said the pedal moves to the floor with the engine on leads me to believe that there are more serious problems than poor settings or reaction disk. I contend that he has not pushed very hard on the pedal at all with the engine off... or that his description is lacking important observations. Please explain to me how a reaction disk would allow the pedal to drop to the floor... ultimately it has to move hydraulic fluid somewhere in order for the master cylinder piston to move through the bore. reaction disk or not. second.... the fact that he replaced the master cylinder without ever bleeding the rear brakes is a DEAD RINGER for improper bleeding for the service performed... You MUST!!! bleed the entire system when you replace the master cylinder. good luck... I just finished flushing my brakes with ATE and the car is on the trailer for a fun 3 day track event at Roebling Road in Georgia.... I will catch up on this next week..... Quote Link to comment Share on other sites More sharing options...
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