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  • s14 braking effort too low

    I have been struggling for a while with what I feel is too little pedal pressure required to reach lockup with my brakes. My current setup is Def’s budget baller fronts with z32 rears, braided steel lines all around, z32 master cylinder and dtc30 pads (prior to that hawk blue). The master cylinder proportioning valve has been shimmed to improve the bias.

    Before my 240 I had an old sports racer Renault, it had a non-boosted dual master cylinder brake setup that had a super firm pedal with great modulation. I want that feel (and I’m too lazy to build up a proper dual master cylinder setup). When driving my s14, it feels like I just have to brush my foot on the brake pedal to start approaching threshold braking. This car is a dedicated track car and I always run race brakes pads so I’m not worried about daily driving.

    What are my options? Anyone tried these?

    Is there a bolt on booster that gives significantly less boosting than a s14 abs manual booster (abs system is long gone)?

    Should I buy a brake booster delete plate and buy a smaller master cylinder? I’ve looked into this on other forums and it seems like everyone who has done this cries about too much effort required. This may be linked to the use of street pads….?

    Is there a larger master cylinder than the z32 that bolts up to increase the effort?

  • #2
    Do those who delete the booster also move the pivot on the pedal? That would help decrease effort

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    • #3
      What size Z32 master, they were not all created equal. I went from a 15/16 to a 17/16 over the winter and it made a MUCH bigger difference than I was expecting.

      I still have the booster on, and while by comparison the pedal is squishy now... Screw it, I'm able to modulate, and don't have to actively take my foot off the brake a bit to blip the gas for a down shift to avoid random lockup.

      All I need to do now is learn how to threshold brake with the new setup.
      '95 240sx

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      • #4
        Do you have a manual or an auto booster? Maybe source an S13 manual booster? They don't give much assist at all. My pedal is pretty hard with a 1" bore Z32 MC. I'm debating moving to a 17/16", but I think it might get a little too stiff.
        '18 Chevrolet Volt - Electric fun hatch for DD duty!


        DefSport Koni Sleeve and Spring Perch Buy!!!
        http://www.nissanroadracing.com/showthread.php?t=5902

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        • #5
          BTW - running same brakes as you (well, I did swap to 6 piston Superlites up front, but basically the same piston area).
          '18 Chevrolet Volt - Electric fun hatch for DD duty!


          DefSport Koni Sleeve and Spring Perch Buy!!!
          http://www.nissanroadracing.com/showthread.php?t=5902

          Comment


          • #6
            Full manual brakes here, 5/8" MC up front, 3/4" rear. front brakes are 1.75" superlites w/ 11.75" rotors and DTC70 pads, and rears are Z32 w/ HT-10.

            I can drive this setup all day long and can outbrake some pretty impressive machinery.
            Getting the MCs in the car was an absolute pain in the ass, BUT, I used a reverse mount assembly so the master cylinders are inside the cabin. I wanted to keep as much room as possible under the hood for engine access and to keep heat out of the brake system. now that's done, I wish I had mounted the master cylinders in the engine bay so I could have easier access for maintenance. pulling an MC to change it or rebuild it is a full day job since I have to pull the dash out to get to them. fuuudge.

            If it were me to do over again, I'd find a smaller brake booster and a larger OE master cylinder and see how that feels.
            Originally posted by SoSideways
            I don't care what color they are as long as they are LONG AND HARD.
            '04 G35 Sedan 6MT- The DD
            '96 240SX- The Track Toy

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            • #7
              Interesting because my team feels the same way about our setup on our S13. Z32 brakes all around, 17/16" BMC, DTC-60s up front, DTC-30's in the rear, S14 booster. Definitely feels like there's too much vacuum assist.

              We have been toying with the idea of going manual and making a setup similar to this solution that is done in the BMW E30 crowd: http://www.massivebrakes.com/brake-s...booster-delete

              Either that, or come up with a method that regulates how much vacuum is developed in the booster by tee-ing in an adjustable valve of sorts and then "tune" it to our liking. Never really seen anyone try this. Perhaps it would mess with AFR since it would be unmonitored air coming in?
              Core4 Motorsports
              CLICK HERE for Wilwood FSL6R Radial Bracket & Rear Wilwood BBK GROUP BUY
              S14 VQ AER Endurance Racing Team

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              • #8
                Originally posted by The Arp View Post
                The master cylinder proportioning valve has been shimmed to improve the bias.
                Where can I read more about this?

                Also, here's a good brake calculator if you don't have your own and want to play around with brake parameters:
                http://www.jakelatham.com/radical/in...shtml#CGHeight
                Core4 Motorsports
                CLICK HERE for Wilwood FSL6R Radial Bracket & Rear Wilwood BBK GROUP BUY
                S14 VQ AER Endurance Racing Team

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                • #9
                  There was a thread in the brake subforum I believe. It was long and a bit meandering as are most of our good threads.


                  The general consensus is that for an S13/Z32 MC with an integrated prop. valve, you can use a 5/16" ID x 5/8" OD (I think it's 5/8") to shim the spring and either increase the split point, or to coil bind the spring and eliminate the proportioning effect then use an external prop. valve (that's my plan eventually).
                  '18 Chevrolet Volt - Electric fun hatch for DD duty!


                  DefSport Koni Sleeve and Spring Perch Buy!!!
                  http://www.nissanroadracing.com/showthread.php?t=5902

                  Comment


                  • #10
                    Originally posted by gills View Post
                    Where can I read more about this?

                    Also, here's a good brake calculator if you don't have your own and want to play around with brake parameters:
                    http://www.jakelatham.com/radical/in...shtml#CGHeight

                    Here is where i did mine.
                    http://www.nissanroadracing.com/show...?t=4178&page=4


                    I still have yet to confirm whether or not I went too far or not enough. It is very difficult to find a safe stretch of road where I live to do testing. Too residential....

                    Comment


                    • #11
                      Originally posted by Def View Post
                      Do you have a manual or an auto booster? Maybe source an S13 manual booster? They don't give much assist at all. My pedal is pretty hard with a 1" bore Z32 MC. I'm debating moving to a 17/16", but I think it might get a little too stiff.
                      I think it's my booster I have the big tandem diaphragm abs/automatic booster. I just ordered a manual booster so hopefully that will help. I just found a comparison between the two and mine is huge compared to the manual one.

                      I'm honestly not sure what size z32 MC I'm running I'll have to check when I get home form work.

                      Comment


                      • #12
                        Originally posted by gills View Post
                        Either that, or come up with a method that regulates how much vacuum is developed in the booster by tee-ing in an adjustable valve of sorts and then "tune" it to our liking. Never really seen anyone try this. Perhaps it would mess with AFR since it would be unmonitored air coming in?
                        Heh, I tried exactly this by adding a bleeder by the brake booster which essentially worked as a vacuum leak. the result seemed to help a little but it really felt like a crappy band aid. Not sure if it will affect AFR since there is a check valve on the line going to the booster, but I have a MAP setup so it had no effect for me.

                        I got rid of the bleeder and am now running the "least sensitive" brakes before going custom MC and such...

                        17/16" master, manual booster, defsport front, z32 rear.

                        Comment


                        • #13
                          Originally posted by The Arp View Post
                          I think it's my booster I have the big tandem diaphragm abs/automatic booster. I just ordered a manual booster so hopefully that will help. I just found a comparison between the two and mine is huge compared to the manual one.

                          I'm honestly not sure what size z32 MC I'm running I'll have to check when I get home form work.
                          I just discovered that I'm running the ABS/automatic booster as well. I'm ordering a non-abs manual one ASAP.

                          Do automatics create less vacuum? What exactly is the reasoning behind the dual diaphragm setup for the ABS/automatic cars?
                          Core4 Motorsports
                          CLICK HERE for Wilwood FSL6R Radial Bracket & Rear Wilwood BBK GROUP BUY
                          S14 VQ AER Endurance Racing Team

                          Comment


                          • #14
                            Originally posted by gawdzilla View Post
                            Heh, I tried exactly this by adding a bleeder by the brake booster which essentially worked as a vacuum leak. the result seemed to help a little but it really felt like a crappy band aid. Not sure if it will affect AFR since there is a check valve on the line going to the booster, but I have a MAP setup so it had no effect for me.

                            I got rid of the bleeder and am now running the "least sensitive" brakes before going custom MC and such...

                            17/16" master, manual booster, defsport front, z32 rear.
                            Yea, forgot about the check valve. Crappy band aid as in it felt like **** at your foot or as in WTF am I doing it this way?
                            Core4 Motorsports
                            CLICK HERE for Wilwood FSL6R Radial Bracket & Rear Wilwood BBK GROUP BUY
                            S14 VQ AER Endurance Racing Team

                            Comment


                            • #15
                              Originally posted by gills View Post
                              I just discovered that I'm running the ABS/automatic booster as well. I'm ordering a non-abs manual one ASAP.

                              Do automatics create less vacuum? What exactly is the reasoning behind the dual diaphragm setup for the ABS/automatic cars?
                              I have a non-ABS manual one at the house. want it?
                              Originally posted by SoSideways
                              I don't care what color they are as long as they are LONG AND HARD.
                              '04 G35 Sedan 6MT- The DD
                              '96 240SX- The Track Toy

                              Comment

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