Venture Posted August 20, 2005 Share Posted August 20, 2005 I bought an early zx rear disk conversion kit some time ago for my 280Z, and have only recently installed it. The install went smooth, but I have since ran into a few problems. The first time I push on the brake pedal it goes almost to the floor, if I pump it again it's at perfect pressure. I've ran a 32oz bottle of brake fluid through the system using the "clear hose in a bottle" trick, and bled the master cyliner so I dont think that there is any air in the system. The E-brake lever on the drivers side isn't working, and I don't think that caliper is clamping as hard as the rest. I have two rebuild kits that came with the conversion but I've heared that these calipers are hard to rebuild. I don't want to buy a zx haynes manual just to rebuild the calipers. Has anyone done or could someone do a good write up on how to rebuild calipers. Ive searched but I haven't found anything very helpfull. Thanks. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 20, 2005 Share Posted August 20, 2005 I have also heard that the early ZX rears are a bear to rebuild. Luckily they are also more reliable than the later ZX calipers. The ebrake not working is usually indicative of a stuck caliper. If the caliper is stuck then only the inside brake pad would do anything. You might try to slide the big thing on top back and forth and see if it is stuck. If it moves, then it is probably a stuck piston. If it doesn't then you may be able to break it loose with a BFH and clean it up and reinstall it. I used to have those calipers on my 240Z and I seem to remember taking that big top piece off, but I don't recall how to do it. If I figured it out it probably wasn't that hard... Quote Link to comment Share on other sites More sharing options...
Venture Posted August 20, 2005 Author Share Posted August 20, 2005 I bet that's it. Ill try to break it loose, but if I can't I'll probably just get a rebuilt one. Quote Link to comment Share on other sites More sharing options...
Venture Posted August 21, 2005 Author Share Posted August 21, 2005 Would a stuck piston give me line pressure troubles? Would it make it seem like there was air in the lines? I have bled the heck out of my system but it still feels like there's some air in there. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted August 21, 2005 Share Posted August 21, 2005 Hard to diagnose these things over the internet but it sounds like a master cylinder problem to me. Seems like a stuck caliper means nothing moves. I would tink it would be just like taking the caliper off and capping off the line. If anything a stuck caliper should have less give than a working or leaking one. Maybe your MC is not big enough? Do the new calipers have a bigger volume than the old? Quote Link to comment Share on other sites More sharing options...
Venture Posted August 21, 2005 Author Share Posted August 21, 2005 My master cylinder worked just fine six weeks ago before I did the swap. I've had the Toyota brakes on the front for a while now, but just swapped the rears. They definately have more volume than the old hub cylinders. I'm running the original 280 MC so I suppose it could be to small, but if that was the case would it gain pedal pressure when I pumped it? I checked the rotors today after a little careful driving and that rotor has barely any wear on the outside and very little on the inside. If I press the pedal the rotor wont turn any more but I don't think it has full strength. I'm going to tinker with it right now. I'll let you all know if I figure anything out. Thanks for the help. Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted August 21, 2005 Share Posted August 21, 2005 I think I would jack the car up and let someone hit the brakes so see what is moving or not. I've never rebuilt the early style brakes but, I did the 82/83 style last summer and it was very tough. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted August 21, 2005 Share Posted August 21, 2005 The pressure doesn't bleed off that rapidly on the backstroke. If you just let up the pedal and hit it a second time right away, it will put a slightly larger volume of fluid in the lines. Maybe you just need the larger 15/16 inch bore ZX MC. Also I don't remember you mentioning anything about adjusting or replacing the proportioning valve. I have no experience with this particular swap so i don't know if you need to do anything differently. But it would just make sense that the new discs will need a different balance than the old drums. Finally I remember old posts talking about the stock drums having a check valve to try and keep some residual pressure on them. May want to resurect some of those threads. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 21, 2005 Share Posted August 21, 2005 The pistons on the early ZX rears are not very big. They are a 2 piston, with a bizarre setup. The piston located on the inside of the car pushes the big slider thingy on top, which pulls the outside brake pad against the rotor. The piston further to the outside of the car pushes directly on the inside brake pad. If the big slider thingy doesn't slide, the inside piston will still push the inner brake pad into the rotor, but the outside pad won't move. IME the stock master is too small for the 4 piston caliper upgrade, so adding the calipers on the back is only going to make the problem worse. Even though the rear pistons aren't very big, they're still quite a bit bigger than the wheel cylinders they're replacing. I think if you had stock fronts and rear ZX calipers you could probably get away with the stock master, but increasing the volume of both without adding a bigger master is too much. The proportioning valve might not be right, so the adjustable valve is not a bad idea. I had a similar setup and ran no prop valve at all. Quote Link to comment Share on other sites More sharing options...
Venture Posted August 21, 2005 Author Share Posted August 21, 2005 Well I took the caliper apart and hit the brakes a little, and found a small leak, and the slider thing wasn't sliding very well. I already had the rebuld kits so I figured, what the heck. I rebuilt the caliper this afternoon, and it really wasn't that hard. I have it all back together, but I still have to bleed the lines AGAIN. I have an adjustable proportioning valve but I haven't plumbed it in yet. I was hoping i wouldn't have to. I haven't tried the brakes yet, but I have the feeling Im going to have to upgrade the master and put in that valve. From what I've read, you have to gut the stock proportioning valve to put in the new one. Is that right? Thanks for all the help. Quote Link to comment Share on other sites More sharing options...
Venture Posted August 22, 2005 Author Share Posted August 22, 2005 I just got done bleeding the lines and took it around the block. The brakes feel MUCH better. All four calipers are definitely squeesing now. They are still a little spongy and low to the floor, but whatever I did got the air aout of the lines. I'll definately be upgrading the MC, and installing the prop valve in the near future, but for now the car will get me to and from work. Thanks for all the help. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 22, 2005 Share Posted August 22, 2005 I'm not sure on a 280, but on my 240 I removed the stock prop valve and installed the adjustable one right in it's place. I know its in a different spot on the 280, not sure if you can do the same. Other than that, sounds like you've got it going. Glad to hear that the calipers weren't as tough as I had previously thought. Quote Link to comment Share on other sites More sharing options...
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