Cannonball89 Posted February 11, 2010 Share Posted February 11, 2010 I'm having a problem with my 71 240z, the brakes have been really mushy to about 3/4 of the way down, then get solid, and hardly any modulation before lock up. The brakes still stop the car good enough to drive in traffic, but are really hurt ones confidence. I have gone through almost every part of the system, New calipers New pads New rotors New drums New Master Cylinder Rebuilt Wheel Cylinders New Shoes New Drums I have bled multiple times, including the "Fart" method, to no avail. I have also checked the pushrod depth. I will be looking at the booster next, and I hope that I find the reaction disk is missing, because if it is not, I don't know what else to check. Since this is a website devoted to modifying Z cars, I thought I would ask a question about modifying the reaction disk. The stock reaction disk is rubber, I would assume to increase the amount of modulation, but I am curious if anyone has tried using a block of aluminum or steel the same thickness as the stock rubber disk? Would this give a stiffer pedal? Or is the disk rubber for some reason that will get me killed if I use a metal one. I just might fabricate one out of aluminum while I am working on it to experiment on what the effects would be compared to a rubber one. Just wanted to see if you all had any thoughts on this. Quote Link to comment Share on other sites More sharing options...
Miles Posted February 11, 2010 Share Posted February 11, 2010 Did you bench bleed the MC, adjust the rear shoes, break in the new pads/shoes, adjust the bake peddle travel under the dash? There is a thread in the brake section that deals specifically with the reaction disk. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 11, 2010 Share Posted February 11, 2010 I just might fabricate one out of aluminum while I am working on it to experiment on what the effects would be compared to a rubber one. Just wanted to see if you all had any thoughts on this. You're thinking that being able to modulate brake force is a bad idea? Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted February 11, 2010 Share Posted February 11, 2010 I have a feeling that your reaction disk has popped out. It sounds just like what happend when mine did it. Let us know Quote Link to comment Share on other sites More sharing options...
Cannonball89 Posted February 13, 2010 Author Share Posted February 13, 2010 Well I pulled the master cylinder off, and there was no metal clip holding the pushrod assembly in place, so I figured the previous owner had taken it out and lost it, probably lost the reaction disk as well. The trouble is the pushrod assembly won't come out. I took the booster off the car, and pulled the rubber boot and metal washer away from the pushrod assembly, and the assembly appears to be rusted into the diaphram. The old master cylinder was leaking at the rear, and probably caused brake fluid to initiate the rust. So I have no way right now of telling if the reaction disk is in place or not, and I figure the booster is probably no good now from brake fluid getting into it, my question is, if I get a rebuilt booster, will it come with a new pushrod assembly? Or do I still have to figure out a way to get the old pushrod assembly out? Quote Link to comment Share on other sites More sharing options...
Cannonball89 Posted February 13, 2010 Author Share Posted February 13, 2010 And as far as experimenting with a solid reaction disk, that will have to wait. And I realize that modulation is a good thing, I am just curious what kind of modulation it would have if the reaction disk is solid instead of rubber. But first priority right now is getting the brakes to work as they should in stock form. Also, I have properly adjusted the rear shoes, I did bench bleed the master, I did check pedal travel under the dash, and I did read the sticky about the reaction disk, that's how I found out the reaction disk exists. Quote Link to comment Share on other sites More sharing options...
Miles Posted February 14, 2010 Share Posted February 14, 2010 The booster will come with the push rod. The push rod in the new booster will be secured so that it will not fall out while you install it. BTW you do not have to remove the MC completely to replace the booster. There is enough flex in the hard lines that you can push ithe MC out of the way. That way you will not have to rebleed the MC and brake system. I bought my last booster from Autozone. MSA and Black Dragon have them too. Nissan units are NLA. Quote Link to comment Share on other sites More sharing options...
Cannonball89 Posted February 18, 2010 Author Share Posted February 18, 2010 Just ordered a remanufactured booster today from advance auto. It is $92.96 after the core credit, which is a lot cheaper than MSA or any other place I've seen. They are made by Cardone. Supposed to be at the store friday, will update after the install. Quote Link to comment Share on other sites More sharing options...
Cannonball89 Posted February 25, 2010 Author Share Posted February 25, 2010 Ok, I got the rebuilt booster from advance auto, I installed it Sunday and drove the car to school today. Brakes work great! The reaction disk was definitely the problem. Just one thing though, I will have to take the booster back out and drill out the hole that the pin for the brake pedal goes through, it is too small on the rebuilt unit for the stock pin to go through. Seems like a stupid mistake for a major auto parts rebuilder to overlook, but other than that it is a quality unit. I probably won't be experimenting with any "solid" reaction disks, that was a dumb idea lol. Quote Link to comment Share on other sites More sharing options...
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