mustard-z Posted October 5, 2004 Share Posted October 5, 2004 My brake booster in my auto-x z is bleeding vacuum, and I am thinking that instead of replacing it I may remove it and run the brake system without it. I am pretty sure that I will need to increase the master cylinder bore to accommodate more pressure on the calipers/drums as well as possibly have to change the pivot on the pedal too. The goal is to create a bit stiffer pedal pressure than with the booster, which should make modulation more linear and allow for better at-limit braking. If anyone has elimiated the booster and gone back to manual brakes on a 78z with stock rotors/calipers and drums. I've got Hawk HP plus pads on the front and will have Nissan Comp Rear shoes the next time run the car next year. Maybe some tips or ideas for calculating the master cyl. size or those sort of things? Where to go to find this info? Thanks, Aren Quote Link to comment Share on other sites More sharing options...
2126 Posted October 5, 2004 Share Posted October 5, 2004 Easiest solution.....just fix your vacuum assist (brake booster) unit. Your approach seems a bit unusual when an easy fix is at hand. Increasing the master cylinder bore will not increase the pressure. It will actually decrease it, for any given input on the pedal. It will only increase the volume of brake fluid for a given pedal stroke. Do you have SS flex lines to your front calipers and rear slave cylinders....this will improve brake feel! You will likely get more input from the other people here...be patient. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 5, 2004 Share Posted October 5, 2004 There is an appropriate ratio of pedal stroke to m/c size to pedal effort. Seems to me that most people running non-boosted systems like Tilton masters run about the same size master (maybe 1 step smaller), but the pedal ratio is a lot different so that you don't have to stand on the pedal to get the car to slow down. I agree with 2126 though, easiest thing is to find a used booster that works. Quote Link to comment Share on other sites More sharing options...
mustard-z Posted October 5, 2004 Author Share Posted October 5, 2004 the problem that I am running into is that it is too easy to apply too much pressure on the brakes. I do have the SS lines on all four corners and with good grippy pads if you breath wrong the tires are being locked up. my thought was that if I replace the booster I will still have to adjust the modulation, and therefore probably have to buy a new pedal and MC. If i just yank the booster out, and replace the pedal and MC I have saved money ( ie. no new booster) Quote Link to comment Share on other sites More sharing options...
mark Posted October 6, 2004 Share Posted October 6, 2004 Way back when, I removed the booster on my 72 for auto cross. Kept the same master. Worked fine. Hade to make a few parts to get it all to work but it solved the same problem that you are having. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 6, 2004 Share Posted October 6, 2004 Fix the booster and learn how to brake properly. When I ran the dual Tiltons I had 7/8" front and 1" rear with a balance bar and an adjustable prop valve. Pedal effort was high but that's something I prefer for race track use. Quote Link to comment Share on other sites More sharing options...
mustard-z Posted October 6, 2004 Author Share Posted October 6, 2004 WOW! All these tips are great, I asked for how to calculate MC sizes or places to find the info and all I get back is "Fix you're booster and learn how to brake properly" A simple "no, I don't know would suffice, or better yet don't bother even responding." HybridZ is turning into Zcar.com as evidence of this thread, useless responses that don't help. johnc, the reason I want to do this sounds like the same reason you wanted to do it on you're car. jmortenson/mark, thanks for the info Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 6, 2004 Share Posted October 6, 2004 I think I found the answer that you were looking for: http://www.markwilliams.com/technical/pedalRatio.html#CALCULATOR Quote Link to comment Share on other sites More sharing options...
johnc Posted October 6, 2004 Share Posted October 6, 2004 the problem that I am running into is that it is too easy to apply too much pressure on the brakes. From this statement in a previous post of yours I inferred that you were not applying the brakes properly. Myself and dozens of others who have autocrossed 240Zs for years in DS, BSP, SM2, FP, etc. have not had this problem or have been able to adapt. A simple "no, I don't know would suffice, or better yet don't bother even responding." But, I do know. That's why I responded the way I did. Also, depending on the class you want to compete in, removing the brake booster is most likely an illegal modification. HybridZ is turning into Zcar.com as evidence of this thread, useless responses that don't help. You may not like the response, but that doesn't mean its wrong or useless. And insulting the people that run this site won't get you very far. Quote Link to comment Share on other sites More sharing options...
74_5.0L_Z Posted October 7, 2004 Share Posted October 7, 2004 I run mine in Emod, and I have deleted the brake booster. I prefer the brakes without the booster, but I've replaced all the brakes with aftermarket pieces. Here is a list of what I am running: Stock 260Z master cylinder Front 11.5 x 0.81" vented rotors (coleman machine) Outlaw 2800 series 4 piston calipers (1.75" pistons) Rear 10.5" x 0.81" rotors (1985 maxima front discs that have been slightly modified Outlaw 2800 series 4 piston calipers (1.375" pistons) Wilwood propotioning valve in line to rear brakes adjusted to nearly full decrease Hawk HP-Plus pads on all four corners. I love my brakes. My car stops very well. When I take my car to the drag strip, I drive it hard through the traps (and then some) at Orlando Speed World and easily slow it down from 115mph to make the first turn out for the return road. The brakes have great modulation and really don't require too much effort. To delete the brake booster I made a 1/4" aluminum plate that has the bolt patterns for both the booster to master cylinder and booster to firewall concentric with each other. I also dismantled the booster to acquire the push rod that goes from the pedal to the booster, and used it (with slight modification) as the push rod for the master cylinder. As far as using a larger master cylinder, don't bother. Increasing the bore of the master cylinder increases pedal efforts, and the stock 260Z master cylinder provides plenty of capacity. I'm including pictures: one that shows the adapter plate installed less master cylinder, and the other with the MC installed. Oh, and please don't compare us to Zcar.com Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted October 7, 2004 Share Posted October 7, 2004 74 5.0 z, love to see more pics of your adaptor plate and boosterless system. i also agree with john c. after more than 100 auto-x and track events i've learned to use my right foot as the modulator and it seems to work pretty well. used vacuum boosters are relatively inexpensive and aren't prone to frequent failure. i currently run dual tilton masters, similar to what john c stated, with a 6.2:1 pedal ratio. effort is higher than normal on the street but nice for the track. i'm running ross corrigan's big brakes-vented 13's front and the 240sx caliper/solid 280zx rotor rear. i went to upgrade the master to a 280zx model and it wouldn't clear the supercharger, so i found the tilton setup from a racer who was moving from [if i remember correctly] gt2 to gt3. got the masters & modded pedal box. i think when the ls1 goes in the tiltons will come out and the stock booster with 280zx master will be installed. my 2 centzzzzzz Quote Link to comment Share on other sites More sharing options...
mustard-z Posted October 7, 2004 Author Share Posted October 7, 2004 Thanks for the help and specs on some other setups. I didn't mean to get bent outta shape but when I ask a question I am looking for an answer to that question not input on what I should do. Maybe I was unclear in my first post but it is all water under the bridge now. Thanks again to all. Quote Link to comment Share on other sites More sharing options...
Wheeler Posted May 10, 2007 Share Posted May 10, 2007 Anyone have any more info on this? Pictures and or updates (Mustard?). Quote Link to comment Share on other sites More sharing options...
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