ezzzzzzz Posted September 22, 2006 Share Posted September 22, 2006 I completed the four wheel disc conversion on my 71. The parts include 280ZX front calipers/300ZX rotors and rear 240SX calipers/300ZX rotors. I also used the 280ZX 15/16" MC and the stock 280ZX four wheel disc proportioning valve. The old T-valve in the back was gutted. I used MM rear brackets and replaced all flex hoses with teflon/stainless steel braid. I have adjusted the MC pushrod close to where it needs to be (it should be damn near dead-on). The MC was disassembled and cleaned up. I don't believe there is any MC internal leakage. The brakes are fully bled and I can stop the car without panic. There are no external leaks in the system. My brakes are heavy requiring a lot of pedal pressure compared to more modern brakes. Since the car sat for nearly a year I don't recall the original pedal pressure. There is no locking up (front or rear) and it appears the rear calipers are not applying full pressure when looking at the rotor surfaces. I adjusted the cylinders and the parking brake works okay. Are there any suggestions for improving overall performance and rear caliper function for those that have gone before me? Quote Link to comment Share on other sites More sharing options...
blueovalz Posted September 22, 2006 Share Posted September 22, 2006 It certainly sounds as though you've done a thorough "hybridz" job. The only thing left out was perhaps the booster. I may be off base a bit here, but when I did this job, I gutted all proportioning valves completely. My rationale (and the brakes were balanced well enough for the worse situations when I was finished) was that the rear drums have a better leverage than disc brakes do, and with the large difference between the front and rear pistons, the Z's weight distribution, and other factors, I decided to eliminate any proportioning valve. Later, when I used a much larger caliper and rotor assembly in the rear, I was required to add a proportioning valve. My experience has been a pretty firm pedal and responsive brakes with this upgrade. Quote Link to comment Share on other sites More sharing options...
ezzzzzzz Posted September 22, 2006 Author Share Posted September 22, 2006 Well now, I thought about the booster but that would only account for the pedal pressure if it were at fault. I'm reluctant to gut the proportioning valve but may try it anyhow. You're experienced at this stuff and if it worked for you then it should work for me. I'm assuming you used the same parts as I did? It's just a matter of disassembly, reassembly and bleeding the lines again all of which is no major problem. My original thoughts were the 280ZX MC and P valve would work well with the other parts and be a close match for the other components. I also think that maybe the MC is not applying adequate pressure due to leaking past the seal. I throw that out there because I had to clean out the MC after it refused to bench bleed but did not replace any seals. As a side note, the porsche CV jointed axles are working flawlessly. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted September 22, 2006 Share Posted September 22, 2006 As a side note, the porsche CV jointed axles are working flawlessly. As have mine. Quote Link to comment Share on other sites More sharing options...
ezzzzzzz Posted September 22, 2006 Author Share Posted September 22, 2006 Terry, I'm looking at a cutaway picture of a NP valve. What exactly did you remove? I'd like to do this in the car but need to know what goes and what stays. Thanks. Quote Link to comment Share on other sites More sharing options...
ezzzzzzz Posted September 23, 2006 Author Share Posted September 23, 2006 Okay, I gutted a 280Z NP valve. The only obvious difference to the 280ZX NP valve is the missing brake failure switch. If I reassemble with only the end bolts (no spring/piston) then the brake system is effectively reduced from a true dual setup to a single setup. I like a dual system which is still reasonably operational even if there is partial failure front or rear. If you look at the guts there is a long bolt for the front caliper section. That bolt is hollow allowing brake fluid to move from front to back balancing brake pressure via the piston/spring located in the rear caliper section. I intend to block this hole, leave out the piston/spring and reinsert both bolts. I'll swap out the 280ZX NP valve for this unit. That will separate the front and rear into individual systems retaining the dual brake properties but no proportioning at all. It should still work as the front calipers are much larger than the rear calipers. All of this because I do not have the rear braking I was hoping for. If this does not provide desired results the next step will be replacing the MC (possibly leaking internally?). Lastly, I may end up with an inline adjustable proportioning valve. Crap, I hope this works...... I want to drive, not wrench, for a while! Quote Link to comment Share on other sites More sharing options...
ezzzzzzz Posted May 18, 2007 Author Share Posted May 18, 2007 Long over due but I thought I'd let everyone know the outcome. I drove a buddy's 280Z and was astonished at the better stock braking. He mentioned that the booster check valve could be a possible problem accounting for hard brakes in my 240Z. I checked and sure enough. The PO had installed it backwards and I never thought to look. Wow, the braking performance is awesome now. It was worth the upgrade but I wonder what the stock brakes would have done? Quote Link to comment Share on other sites More sharing options...
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