kj280z Posted April 13, 2011 Share Posted April 13, 2011 (edited) Hey all In case you haven't tried to get your hands on a 15/16" 79-80 280zx Master cylinder they are out of stock everywhere and the few I could find were ridiculously priced ($175-$250). Here's my issue: I have the s12W toyota front calipers with 300zx vented rotors up front and the 240sx rear disk conversion from MM. The brakes have always been VERY good... Car sat for awhile and the old Master Cylinder was ready for replacement. I replaced the following items during the refresh: 1. Brand new (not rebuilt) front s12W calipers 2. Porterfield pads all around 3. Rear brakes were fine 4. Replaced the Master cylinder with a Wilwood unit 1" - verified the specs and talked to Wilwood extensively (pic here http://wilwood.com/I...260-8794-lg.jpg) specs here http://wilwood.com/S...spx?itemno=8794 5. The stock prop valve that was on the firewall was eliminated (just made 2 lines to directly connect the lines) - This was done in preparation to add the Wilwood adjustable prop valve which I will install soon After bleeding the system several times, the brakes initially would grab very hard almost all the way at the floor. I then adjusted the actuation rod which extends the rod inside the brake booster... The pedal came up a good amount (not perfect yet though) but they are still very "grabby" - almost like an on/off switch! Impossible to modulate to any degree. Some have said that adjusting the connection at the brake pedal (lengthening it) might help... which I was planning to try... Any thoughts? Would the elimination of that one prop valve (there's 2 in the stock system) cause this condition? Any thoughts on the Wilwood Master Cylinder (it's a nice unit and was $100 via Jegs) - It might be a nice upgrade/option if the 15/16's are getting harder to find and we can find a way to make it work correctly. We checked the stroke and volume against the stock unit and it is virtually the same (I seem to remember 1.12") and Wilwood was confident it would be a great replacement to the stock unit I'm at a loss - maybe you guys have some ideas... Thanks in advance! Edited April 13, 2011 by kj280z Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 13, 2011 Share Posted April 13, 2011 Sounds like a reaction disk issue. Quote Link to comment Share on other sites More sharing options...
kj280z Posted April 13, 2011 Author Share Posted April 13, 2011 (edited) Yeah - I was afraid of that - I had the booster out to paint the engine compartment and I shook it around and it seemed fine and no rubber parts bouncing around inside, but it's the only thing that's logical... although with the different master cylinder I was wondering if that may be the culprit... doubtful but I thought I'd ask... Edited April 13, 2011 by kj280z Quote Link to comment Share on other sites More sharing options...
johnc Posted April 13, 2011 Share Posted April 13, 2011 A 1" MC will require less travel but more pedal pressure to get the same braking force as a 15/16". Quote Link to comment Share on other sites More sharing options...
kj280z Posted April 15, 2011 Author Share Posted April 15, 2011 (edited) I have an update They show 2 different brake boosters as available for the 75-76 280z (probably other years as well) There's a 8 inch and a 10 inch version... The 8 inch version is the one I had in my Z (1975) Unfortunately the 8 inch version would have taken 3 weeks and the 10 inch version was available immediately. I decided to try the 10 inch version... I have a question about this booster - Was there a larger version to provide additional assist for some reason? I also have noticed that later Z's had the larger booster and also had the 15/16 master cylinder... Is this because the 15/16 Master cylinder requires more pedal effort so the larger booster provided more assist? Just curious about the differences. Anyway - I have the wilwood 1" master with the 10 inch booster and this seems like a real nice combination! Solved my "stabbiness" problem - I will however have to adjust the actuation rod slightly as the brakes grab just a small amount too close to the floor - some might find it fine the way it is, but I'd like to raise it... Thanks for your help - and if anyone knows the deal with the different size boosters I'd love to know Also, the reaction disk was rattling around inside my old booster - I'll take it apart and post some pics in a few days - gotta get my seat brackets fabbed first! Edited April 15, 2011 by kj280z Quote Link to comment Share on other sites More sharing options...
zcarnut Posted April 15, 2011 Share Posted April 15, 2011 They show 2 different brake boosters as available for the 75-76 280z (probably other years as well). There's a 8 inch and a 10 inch version... I have a question about this booster - Was there a larger version to provide additional assist for some reason? ...if anyone knows the deal with the different size boosters I'd love to know... There's a simple explanation: The 2+2 (the four seaters) S30 Z cars used the larger booster. Quote Link to comment Share on other sites More sharing options...
kj280z Posted April 15, 2011 Author Share Posted April 15, 2011 There's a simple explanation: The 2+2 (the four seaters) S30 Z cars used the larger booster. Hmmm not really... Did the 2+2 have a higher capacity Master Cylinder? If so, were they compensating for the additional pedal effort that it would require? Were they trying to compensate for the additional weight but kept the same master Thus trying to allow more assist with a larger brake booster? Does the larger brake booster even provide more assist? Maybe there was a different reason for it in the 2+2? I've never seen any data that depicts how much assist a given booster provides... have you? Quote Link to comment Share on other sites More sharing options...
zcarnut Posted April 16, 2011 Share Posted April 16, 2011 Did the 2+2 have a higher capacity Master Cylinder? No, it was not needed. The 2+2’s used the same size calipers and rear cylinders as the 2-seaters so the fluid volume displacement is the same. Were they trying to compensate for the additional weight but kept the same master Thus trying to allow more assist with a larger brake booster? Yes, exactly. A heavier car requires more braking force. Does the larger brake booster even provide more assist? Yes. A larger diameter = larger area for the vacuum to act on, thus increasing the pedal force even more than the 7.5†diameter booster. Some brake booster theory: http://www.autoshop101.com/forms/brake05.pdf http://www.classicperform.com/PDFs/BoosterBrakePressureChart.pdf Maybe there was a different reason for it in the 2+2? I've never seen any data that depicts how much assist a given booster provides... have you? Unfortunately, there’s only service info in the repair manuals. I have seen output force vs. input force (or gain curves) for some typical boosters in SAE engineering texts. Similar to these curves: http://www.fte.de/oe_bremssysteme_bremskraftverstaerker_en.FTE Quote Link to comment Share on other sites More sharing options...
jasper Posted April 16, 2011 Share Posted April 16, 2011 So, for clarification, it WAS the reaction disc,(out of place) causing the problem. (on/off/stabiness) YES??? You replaced it with a 10" remanufactured unit, and solved the problem, and gained more assist, as a bonus. Quote Link to comment Share on other sites More sharing options...
kj280z Posted April 16, 2011 Author Share Posted April 16, 2011 (edited) So, for clarification, it WAS the reaction disc,(out of place) causing the problem. (on/off/stabiness) YES??? You replaced it with a 10" remanufactured unit, and solved the problem, and gained more assist, as a bonus. The general answer would be YES the reaction disk was rattling around in the bottom of the booster (I'm going to take it apart and repair it so I have a spare) - although I cannot comment if I have more assist or not... I've only driven it a few miles since the replacement, but the stabiness is gone. In general the Wilwood master cylinder seems to be performing well. The only modification to make it a direct bolt on is to enlarge the mounting holes slightly and I had to make 2 new hard lines to adapt the threads for the MC to the Prop valve below - took a total of 20 minutes! Easy! Also, it's a good idea to lengthen the actuation rod between the MC and the booster - it's adjustable That's the last adjustment that I'll do tomorrow to bring the pedal up slightly... All-in-all I'm really happy with my braking system now! The S12W calipers with vented rotors have always served me well combined (with the porterfield pads) with the MM 240sx rear setup - the addition of the wilwood MS and this new booster seem to round out the system quite nicely! Edited April 16, 2011 by kj280z Quote Link to comment Share on other sites More sharing options...
z-ya Posted April 16, 2011 Share Posted April 16, 2011 Ken, If you find that your right thigh muscle is getting larger, it is probably that 1" MC . The stock 7/8" MC should work fine with the setup you are running. No need for a larger MC. Pete Quote Link to comment Share on other sites More sharing options...
kj280z Posted April 16, 2011 Author Share Posted April 16, 2011 Ken, If you find that your right thigh muscle is getting larger, it is probably that 1" MC . The stock 7/8" MC should work fine with the setup you are running. No need for a larger MC. Pete It's actually much better than you'd expect! Less pedal effort than my Dad's stock 240z from what I can tell so far! Quote Link to comment Share on other sites More sharing options...
spitz17 Posted June 7, 2011 Share Posted June 7, 2011 I am curious to where you bought your "brand new" s12w calipers. Would you please share? Quote Link to comment Share on other sites More sharing options...
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