daddydonuts Posted March 31, 2014 Share Posted March 31, 2014 (edited) I have searched diligently and can't find any definitive answers. 73 240Z, ZX rear caliper disc conversion w/maxima offset brackets, Toyota S12+8 front 4 piston caliper conversion, new 15/16 MC, new booster for a 240Z. Problem is my brake pedal has no clamping force when the brakes are applied when the engine is running. Brakes are bled properly, I think its a bad booster, but I got that new from O'Reilly auto. MC pushrod is adjusted properly. I am ordering a new check valve to eliminate that. No leaks on any vaccum lines. No leaks anywhere on the car. Any suggestions as to why my brake pedal goes all the way to the floor when the engine is running? The brakes will build pressure when the engine is off, by pumping the brakes. Edited March 31, 2014 by daddydonuts Quote Link to comment Share on other sites More sharing options...
Miles Posted March 31, 2014 Share Posted March 31, 2014 (edited) Go to the brake/FAQ forums and read up on "missing reaction disk". Many many threads on your exact problem. Example: http://forums.hybridz.org/topic/69706-reaction-disk-pictures-and-walkthrough/?hl=%2Breaction+%2Bdisk Edited March 31, 2014 by Miles Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted March 31, 2014 Author Share Posted March 31, 2014 Go to the brake/FAQ forums and read up on "missing reaction disk". Many many threads on your exact problem. Example: http://forums.hybridz.org/topic/69706-reaction-disk-pictures-and-walkthrough/?hl=%2Breaction+%2Bdisk Thanks, I had a new, (reman) booster...will be checking that tonight. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted March 31, 2014 Author Share Posted March 31, 2014 Took my booster off and took out the push rod and my reaction disc is there and is held in place by grease as it should be. What is my next place to look...? I am going to replace some hard lines, but that is not an issue with my pedal going all the way to the floor. Could it be the check valve? Quote Link to comment Share on other sites More sharing options...
Miles Posted March 31, 2014 Share Posted March 31, 2014 A defective check valve would not cause your problem. Check list: Did you bench bleed the MC? Many threads on this. Did you get all of the air out of each caliper? On my 240SX calipers I had to remove them and tilt/shake them to get the air out. Do you know that the 15/16 MC requires adjusting the push rod out i.e., longer? Many threads on this. Did you install the aluminum spacer between the booster and the MC? I have seen people do this and then wonder why the pedal throw is so long. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted April 1, 2014 Author Share Posted April 1, 2014 (edited) <p> A defective check valve would not cause your problem. Check list: Did you bench bleed the MC? Many threads on this. Did you get all of the air out of each caliper? On my 240SX calipers I had to remove them and tilt/shake them to get the air out. Do you know that the 15/16 MC requires adjusting the push rod out i.e., longer? Many threads on this. Did you install the aluminum spacer between the booster and the MC? I have seen people do this and then wonder why the pedal throw is so long. Yes to everything except I'm going to go back and recheck to make sure I have all of the air out of the lines. I have a friend who is a mechanic and he said that sounds like my problem. Edited April 1, 2014 by daddydonuts Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 1, 2014 Share Posted April 1, 2014 Did you add the part about pumping the brakes, in the first post? Didn't see it yesterday. That says air in the system. These types of swaps, in general, seem to be notorious for not having the bleed hole at the very top of the caliper's internal passages, when mounted. Even off just a little bit, the air will sit there while the fluid flows out the bleed hole. The external hole may not be a direct shot to the internal high point either. They all seem to take some finagling. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted April 1, 2014 Author Share Posted April 1, 2014 Did you add the part about pumping the brakes, in the first post? Didn't see it yesterday. That says air in the system. These types of swaps, in general, seem to be notorious for not having the bleed hole at the very top of the caliper's internal passages, when mounted. Even off just a little bit, the air will sit there while the fluid flows out the bleed hole. The external hole may not be a direct shot to the internal high point either. They all seem to take some finagling. I will move the calipers around when I bleed tomorrow. It has to be air in the system, everything is new or reman'd or rebuilt with new seals. Quote Link to comment Share on other sites More sharing options...
seattlejester Posted April 2, 2014 Share Posted April 2, 2014 Tighten all the brake line fittings? How are your brake lines? If possible you should try and bleed both the rears at the same time and both the fronts at the same time. Easily done by yourself with a piece of tubing submerged in a reservoir of brake fluid. That was my final solution to my problem after everything was checked. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted April 2, 2014 Author Share Posted April 2, 2014 Tighten all the brake line fittings? How are your brake lines? If possible you should try and bleed both the rears at the same time and both the fronts at the same time. Easily done by yourself with a piece of tubing submerged in a reservoir of brake fluid. That was my final solution to my problem after everything was checked. That's how I plan to do it Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted April 3, 2014 Author Share Posted April 3, 2014 (edited) OK if anyone has this problem that I did, where there was no brake pressure with the engine running while applying pressure to the brake pedal and weak pressure with the engine off. Look for small kinks in your hard brake lines and replace as needed, ensure your brake pedal height is adjusted very very very close to specs, 7.99 inches from the front of the brake pad to the floor pan that is perpidicular to the pedal, not the firewall. This was my two issues that I overlooked and I will be beating the crap out of myself later for that. Thanks for giving me advice HZ! Edited April 3, 2014 by daddydonuts Quote Link to comment Share on other sites More sharing options...
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