383 240z Posted October 19, 2006 Share Posted October 19, 2006 I was wondering if I could have some of the local talent on here help me, off forum with a problem I'm having with another rig I'm building. What it boils down to is master cyl sizing. Here are the specs. 4 wheel discs 1 piston at each caliper. front pistons are 2.75" rears are 2.50" -3 flexlines 3/16" hard lines 9" booster 2:1 pedal ratio. Any insight anybody can lend will be of great help. Keith Quote Link to comment Share on other sites More sharing options...
blueovalz Posted October 20, 2006 Share Posted October 20, 2006 Rough guess on following figures but I think it will be pretty close. On my Z I have about 6:1 pedal ratio, a .9375" MC and a 2.375" slave (caliper) cylinder. Thus, for every 40 pounds pressure I place on the brake pedal, I place roughly 1535 pounds of clamping pressure on the rotors (I am not including any booster assistance). This set-up provides more than adequate performance With the parameters you've provided, and for the same clamping pressure, you'd need a .627" (5/8") MC. The only problem I see at this time, is the required travel to move enough fluid to clamp the rotor. You'll get the required MC piston travel with the long 2:1 pedal ratio, but I don't think they make a master cylinder long enough for this purpose. Yes, you could use a larger MC to reduce travel, but then it would require more pedal pressure. Hope this helps Quote Link to comment Share on other sites More sharing options...
383 240z Posted October 20, 2006 Author Share Posted October 20, 2006 I've been in contact with wilwood tech on this and have been getting conflicting answers, some say my 1" master is fine, others want me to buy their 1 1/8" master. I was thinking that the front calipers in their stock form were fed by a 1 1/8" master, so I should use that and an adj. prop. valve to cut down the rear. This is for my off-road Jeep, I'm not to worried about pedal input psi as much as I am with travel. I'll be removing the stock propvalv this week, do you think I should just "T" the front calipers and put the adj. prop valve on the rears? Keith Quote Link to comment Share on other sites More sharing options...
blueovalz Posted October 20, 2006 Share Posted October 20, 2006 To me, it sounds like the larger MC (as has been recommended) is too large for the abnormal pedal ratio. Just wondering if you do any power lifting, squats? Lastly, you may want to review the area where the MC is located and insure it will be up to the task of heavy pedal pressures. On the typical firewall mounted systems, the wall can flex a bit. A Tee fitting will be fine up front, and with the relatively large rear caliper piston, I would definitly use the proportioning valve. If the CG is pretty high off the ground, you'll get a lot of weight off the rear during braking, and this will make it tough to adjust out. Quote Link to comment Share on other sites More sharing options...
383 240z Posted October 23, 2006 Author Share Posted October 23, 2006 I'm wondering why you said abnormal? It is a factory pedal booster setup. I'll re-measure today but I believe from the piviot point to the hook up for the master is around 4" then from the master hook up to the center of the pedal is another 8". Does this not give me a 2:1 ratio? Math never really was my strong suit. I'm planning on pulling it in the shop this week and removing the factory prop/meteriing valve and seeing what the 1" master does. Thanks for all you help so far. Keith Quote Link to comment Share on other sites More sharing options...
blueovalz Posted October 23, 2006 Share Posted October 23, 2006 You are correct. I was looking at it the pedal ratio differently (your total length of pedal : the length from MC rod to pivot point (3:1 ratio). This does help you quite a bit. Quote Link to comment Share on other sites More sharing options...
383 240z Posted October 24, 2006 Author Share Posted October 24, 2006 I have the valving on my front shocks a little stiffer to keep it from nose diving under hard braking, and steep down hill decents. I have reinforced the firewall a while ago, as Jeeps are known for thin flexy firewalls. It is 32* in the shop now so I'm not working out there today. I'll let you know what I find when I get back on that project this weekend. Keith Quote Link to comment Share on other sites More sharing options...
Guest mrobertweiss Posted October 27, 2006 Share Posted October 27, 2006 go to mpbrakes.com for the tech section, many of your questions are dealt with, there. Quote Link to comment Share on other sites More sharing options...
383 240z Posted October 30, 2006 Author Share Posted October 30, 2006 I just tried to access the tech section, they only allow customers to view it. Thanks for the tip anyway. Keith Quote Link to comment Share on other sites More sharing options...
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