heavy85 Posted July 29, 2006 Share Posted July 29, 2006 I have the classic light pedal at the top with engine running issue. Trying to look into see if I have the reaction disk problem, but when I took the master off it looks like this. As you can see there is a serated locking ring the keeps the seal in place. Without destroying this ring I'm not sure how to take this out? You can pull the rod out somewhat but obviously not all the way since the seal and lock ring are in the way. I'm thinking the reaction disk is in place because in order to get the rod back in place you have to line it up exactly with some sort of pilot on the other end. I'm thinking this pilot hole is the reaction disk so it's in place - is that correct? PS - this is a reman booster from Napa I bought a couple years ago. Thanks Cameron Quote Link to comment Share on other sites More sharing options...
J__ Posted July 30, 2006 Share Posted July 30, 2006 i just had to take that rod out today to check the reaction disk. that metal clip u see is very easy to take out. just get avery small flat head screw driver and GENTLY pry it out try not to bend it. but if u do, its fairly easy to bend back into shape. after u get the clip out. the rest just pull out. then u can look into the hole to see if u see the reaction disk. for me, the reaction disk was stuck on the plunger still thank god.. i just pried it off and super glue it down just in case. now im more confused.... reaction disk is in place but brakes still bottom out without any resistance........ Quote Link to comment Share on other sites More sharing options...
Forrest Posted July 30, 2006 Share Posted July 30, 2006 If you pull on the rod hard enough, the locking ring will come out without being damaged - the seal will put even pressure along the back of the ring Quote Link to comment Share on other sites More sharing options...
240playtoy Posted August 2, 2006 Share Posted August 2, 2006 Just moving the plunger in and out doesn't mean your reaction disk is still in place. The reaction disk sits in a metal recess and the plunger moves into it as well. Check this for visual (my reaction disk is missing in the pictures). I do immediately notice a difference between your booster and mine (240z). Your adjusting nut in your picture appear to be between 1/4" and 1/2" longer than that on the 240. I now know why massive adjustment of mine was needed to remove my excessive pedal movement. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted August 3, 2006 Author Share Posted August 3, 2006 Just moving the plunger in and out doesn't mean your reaction disk is still in place. The reaction disk sits in a metal recess and the plunger moves into it as well. Check this for visual (my reaction disk is missing in the pictures)[/url']. I do immediately notice a difference between your booster and mine (240z). Your adjusting nut in your picture appear to be between 1/4" and 1/2" longer than that on the 240. I now know why massive adjustment of mine was needed to remove my excessive pedal movement. Interesting since mine is also a 240. I checked and the reaction disk is in place. I'm wonder if the combination of booster and master is a miss-match of different years that are not quite compatible? Maybe I should try to screw that plunger out even more as I've never touched it? Thanks Cameron PS - sorry for the HUGE picture Quote Link to comment Share on other sites More sharing options...
240playtoy Posted August 3, 2006 Share Posted August 3, 2006 I had to adjust mine due to using one of the ZX masters. But then, I think I also had an aluminum diamond spacer that went over all four of the bolts on the booster (~1/2" thick). In addition, your MC housing looks like it's got a deeper "shroud" on the back end of it than my original did. Does your MC fit flush against your booster without you having to tighten it down? Quote Link to comment Share on other sites More sharing options...
heavy85 Posted August 3, 2006 Author Share Posted August 3, 2006 I had to adjust mine due to using one of the ZX masters. But then, I think I also had an aluminum diamond spacer that went over all four of the bolts on the booster (~1/2" thick). In addition, your MC housing looks like it's got a deeper "shroud" on the back end of it than my original did. Does your MC fit flush against your booster without you having to tighten it down? Mine's got the aluminum spacer just not in the pics. And yes I can fit the MC flush without tighening the nuts. Thanks Cameron Quote Link to comment Share on other sites More sharing options...
heavy85 Posted August 4, 2006 Author Share Posted August 4, 2006 And yes I can fit the MC flush without tighening the nuts. I think that's my problem. The pushrod was almost all the way screwed in. Tonight I backed it out probably 3/8" and your can now feel the pushrod begin to push the MC piston roughly 1/8-1/4" before the MC is flush the the spacer. I'm wondering now how much preload should there be on it as I don't want to drag the brakes? I'm thinking just a very slight amount like a mm or two? Thanks Cameron Quote Link to comment Share on other sites More sharing options...
240playtoy Posted August 4, 2006 Share Posted August 4, 2006 I don't know about pre-loading, if there needs to be some, then I need find a different adjusting screw as mine is out as far as it will go without falling out. I probably have less than a mm between my rod and piston, less than an inch of travel in my pedal before I get resistance. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 4, 2006 Share Posted August 4, 2006 DO NOT, DO NOT, DO NOT preload the brakes. EVER!!! The master cylinder needs to fully release in order to open up the little ports that let the brake fluid back into the reservoir. If they can't release ALL THE WAY then they can't release the pressure. This makes no difference at first, because you let off the brake and there is no pressure, then you step on them and there is, let off and there isn't. As the brakes gets hotter from you applying the brakes, say, in traffic, the heat generated transfers into the fluid, which expands. If the pressure can't release back into the master cylinder reservoir then this results in a light drag on the brakes. As the drag continues, more heat is generated, more fluid expansion, more pressure, more heat, more expansion, more pressure, etc. I had this happen with my clutch once and I learned to have free play in the system. On the brakes you want a little free play in the master to booster connection, and you want a little in the pedal to the booster connection. 1/8" of free play in both won't make a noticeable difference in the pedal throw, but not having that free play will be a BIG problem. Quote Link to comment Share on other sites More sharing options...
240playtoy Posted August 4, 2006 Share Posted August 4, 2006 Gracias, Jon. I thought I'd seen something about that in a thread about how the cylinder works, but I figured I'd stay away from that as I didn't know much about it. Quote Link to comment Share on other sites More sharing options...
5 Star Rising Posted September 23, 2006 Share Posted September 23, 2006 I noticed alot of you have similar problems as I do. Where your brake pedal goes to the floor,after endless Master Cyls,gallons of brake fluid from bleeding.Has anyone found and solved this problem yet lol? Hmmm I wrench on trucks for a living and have never had this problem with brakes before. I have put 4 different master cyls on not including the one that came with my car. 3 remans and the latest one is a New MS. Still pedal goes to the floor,I bled the system 20 times even using a power bleeder. I replaced my front calipers with remans.replaced rubber brake lines and all short metal lines,bench bled all MS's,swapped my prop valve with another used one,checked and adjusted my rear drum brakes,made sure my caliper bleeders were on top,adjusted out my push rod that pushes my MS. When there car is off I can pump up the pedal firm and hold it, but when I start the car the pedal goes to the floor and the brake light comes on. I just bought the car recently and drove it for the first time tonight whoa it was scary lol I locked up my rear brakes on some fallen leafs on my street. What exactly does the reaction disc do? If mine has fallen off will it still push out the rod into the MS? I unbolted and pulled my MS away from the booster. I then started the car and reached around and put my hand over the rod,I pressed the brake pedal and the rod pushed all the way out like it should i would amagine.Does this mean its working correctly? I have been on this brake problem for 2 weeks straight. Any help or tips would be awesome.. Rob Quote Link to comment Share on other sites More sharing options...
240playtoy Posted September 23, 2006 Share Posted September 23, 2006 As far as I can tell from what it does when it's gone, the reaction disk seems to allow your booster to modulate the force being applied to the MC. All the booster mechanisms still move when the reaction disk is missing, the only thing that's different is that when you press down on your pedal. You'll get essentially no braking power until a point, then nearly full braking power (locked up brakes). If all of your MC's (including your original) appear to "have the same problem" in that the pedal is soft, it's a very good chance it's your RD. Is your brake system stock? No swaps of different year MC's, boosters or anything like that? The one thing that's confusing me is that your brake light comes on, I don't remember that happening when I was having my myriad of brake problems. In my 240 only 2 things turn that light on, my parking brake and that "distribution" block the MC feeds into. I believe it shuts off front or back brakes if there's a loss of pressure on one side? Quote Link to comment Share on other sites More sharing options...
5 Star Rising Posted September 26, 2006 Share Posted September 26, 2006 I pulled open my brake booster and yes my reaction disk was gone. I got a RD,glued it to the rod and cafefully installed it. When I went to check my pedal it felt the same,went to the floor, and my brake light came on. Just before lighting the match to burn the car to the ground I decided to check my rod adjustment again that pushes into the MS.For the hell of it I unscrewed it almost all the way out and installed my MS. Amazingly my brake light went out and the pedal actually felt hard for a change while the car was running. But of course my brakes would be dragging at this point. I took it around the block anyway and my car could stop on a dime. The pedal felt great,the light was out, but the brake were dragging.I knew that I would have to spin the rod in abit and measure the adjustment. Well I spent 2 hours trying to get the rod just right. If I adjusted the rod out too far the pedal would feel great ,the brake light would go out,but the brakes would drag.. If I went in to far the brake light would come on, the pedal would have too much freeplay and would not want to springback like a normal pedal. No matter how many times I would adjust the rod I could never find "The sweet spot" Even with fractions of a turn per adjustment. Then I said screw it and took the car for a little farther test drive like 3 blocks. All of a sudden while driving, the car started bogging and started feeling like I was towing a huge boat behind me,I turned around to head home but did not make it. My brakes gradually all locked up completely and the pedal became ROCK hard (so hard that I could barely turn my brake lights on. I had to almost burn up the clutch just to get out of the road and pull over.. What happened here?? Has anyone heard of this happening? I'm thinking the MS rod vibrated out while driving maybe, because after adjusting it so many times it became easy enough to adjust with your fingers. Any one have any input for this one??? I stumped Quote Link to comment Share on other sites More sharing options...
DCZ Posted September 26, 2006 Share Posted September 26, 2006 5 Star Rising - Sounds like your reaction disk fell off somewhere in all that adjusting. The "brakes gradually locking up while driving" symptom is exactly what happened to mine when I let the reaction disk fall. I had to take the Booster off, hold it flat so the Master Cylinder side was pointing up, then shake it violently and let the reaction disk fall down into the "well". Then re-install making sure the rod doesn't pull out and let the reaction disk fall again. Very frustrating, I know. Here's a good tip: If you find yourself in this situation (brakes locked up due to reaction disk missing), you can loosen the nuts holding the Master Cylinder onto the Booster so that the M/C can pull about 1/4" away from the booster. Don't take them completely off, you don't want the M/C to be hanging in the breeze. This way you have enough brake to limp back home but the brakes won't lock up. Quote Link to comment Share on other sites More sharing options...
Miles Posted September 26, 2006 Share Posted September 26, 2006 5 Star I carry a 10mm tubing wrench with me when I am adjusting and testing the push rod length. When the brakes lock up from too much push rod you can releive the pressure in the brake lines by cracking open the MC bleed screws. I do my test drives near my house and this gets me home every time when the brakes lock up. Miles Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 26, 2006 Share Posted September 26, 2006 Miles has it. The pushrod is too long, so the master cylinder can't retract all the way. This means that the little port to the reservoir on the master isn't opening up, so whatever pressure is in the brake master is stuck in there. What happens is you keep using the brakes, and the fluid gets hotter and expands, which puts the brakes on more, which gets the fluid hotter, etc until you can't drive anymore. If you opened the bleeder like Miles did then it would drive normally again for a while until this whole cycle started over. Bottom line is the pushrod is adjusted too far out. Adjust it back in. You MUST have free play in there, or else this is the result. Quote Link to comment Share on other sites More sharing options...
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