DCZ 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. Maybe a simple question but, how do you "check" the reaction disk with everything installed on the car? Can I unbolt the master cylinder keeping the fluid lines attached, pull it away from the booster and stick my finger in there? Is it possible to look in the booster and see it? Seems like the booster rod is in the way. I have a similar problem in that the pedal is VERY easy to push with only slight braking action for the first few inches and then WHAM! the brakes instantly grab. I'm trying to figure out whether it is just air in the lines, a maladjusted booster rod or a fallen reaction disk. Stock 73 240z brake system. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 15, 2006 Share Posted June 15, 2006 That also sounds like a reaction disk problem DCZ. Search for reaction disk and you'll find a very recent post where a guy took pictures of it. Basically you should be able to unbolt the master and pull it off the studs with everything else still attached, then pull the booster rod and look for it. If you don't see it you can try to fish around in the bottom of the booster, or you can just take the booster off and shake it until the disk comes out. Either way, reposition the disk and reassemble. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 15, 2006 Share Posted June 15, 2006 John, two most common posts for reaction disk are as follows: 1. I've bled my system 437 times and the pedal still hits the floor. Pedal feels great when the engine is off. 2. Pedal has no feeling and goes straight to the floor then all the brakes lock and car screeches to a stop. EDIT--I should also say that I've never actually had this problem myself, but I've seen it so many times that I'm just used to seeing the complaints at this point. Quote Link to comment Share on other sites More sharing options...
bjhines Posted June 15, 2006 Share Posted June 15, 2006 I hear you.... I just dont see it actually happening... I troubleshoot home brake jobs often enough for people in my club... I have never seen the disk problem either... but what I have found is that peoples descriptions of their problems are inaccurate most of the time... If someone understands the system.. they would not have problems in the first place... It is ok to learn the hard way.. better to learn on your own with help from others when needed.... I would not entirely discount the reaction disk (assuming the pedal does not ACTUALLY go to the floor)... but I would suggest that you bleed the entire system FIRST... Quote Link to comment Share on other sites More sharing options...
DCZ Posted June 15, 2006 Share Posted June 15, 2006 I hear you.... I just dont see it actually happening... I troubleshoot home brake jobs often enough for people in my club..... OK John, grab your bullet-proof vest and come on over to Durham. Beer is in the fridge! LOL! Damian Jon M - thanks for the info. Last time I "just took the booster off" cost me several scraped knuckles, a bonked head (watch out for that steering column!) and a bunch of cursing. Quote Link to comment Share on other sites More sharing options...
srgunz Posted June 15, 2006 Share Posted June 15, 2006 REACTION DISC. The telltale symptom of missing reaction disc is fairly good pedal with engine off. Then goes to floor when engine runs. For those that have the fronts grab and put you thru the windshield more than likely have the same problem but have adjusted the booster rod length to make up for reaction disc missing. I spent a whole summer one year chasing this problem even making the mistake of lengthing the booster rod. That is a no-no with reaction disc missing. Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted June 15, 2006 Share Posted June 15, 2006 here's a link to where i posted info when i chased down my reaction disc-there's another link withing the post to pics in my gallery of the vac booster internals. perhaps one of the moderaters can sticky that one for us [hint, hint]. david http://forums.hybridz.org/showthread.php?t=110874 Quote Link to comment Share on other sites More sharing options...
Z24O Posted June 16, 2006 Author Share Posted June 16, 2006 thanks guys looks like i've got some leads to follow/check over the weekend will post how i went next week Quote Link to comment Share on other sites More sharing options...
DCZ Posted June 26, 2006 Share Posted June 26, 2006 REACTION DISC.The telltale symptom of missing reaction disc is fairly good pedal with engine off. Then goes to floor when engine runs. For those that have the fronts grab and put you thru the windshield more than likely have the same problem but have adjusted the booster rod length to make up for reaction disc missing. I spent a whole summer one year chasing this problem even making the mistake of lengthing the booster rod. That is a no-no with reaction disc missing. Well it looks like this was the problem I was having. I pulled the booster off the car but could not see any way to pull the pushrod out or otherwise access the inside of the booster without twisting the two halves apart like the service manual shows. So I held the booster with the master cylinder side pointing straight up, held the pushrod up and out of the way, and shook the booster so that the reaction disk could fall back down into the "well". IT WORKED! I couldn't tell by looking at it, but I put it back on without doing anything else and the brakes are working properly. Pedal is high and firm, just like Lindsay Lohan's . . . well, you get the idea. Just wanted to bring this thread back up to confirm that the symptoms above can be caused by a missing reaction disk and that you can shake it back into place without taking apart the booster. Quote Link to comment Share on other sites More sharing options...
bjhines Posted June 26, 2006 Share Posted June 26, 2006 Hey nice work!!!!! .... I still can't agree with the pedal actually dropping all the way to the floor.... I think you will find that pedal to the floor is quite a bit different than the action you were describing.... Quote Link to comment Share on other sites More sharing options...
DCZ Posted June 26, 2006 Share Posted June 26, 2006 My pedal wouldn't drop to the floor. It gave very little resistance until it was pretty far in it's travel and then it was solid. I think the only way you could get the brake pedal to the floor would be if you had air in the lines. Quote Link to comment Share on other sites More sharing options...
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