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  • Brakes working too good...

    I only upgraded my fronts to the Wilwood 6 piston, rears are stock, and basically the brakes are working too good. Too good for the tires at least as the front wheels lock up under hard braking if I'm not careful.

    Overall the brakes work phenomenal but I have to condition myself to not stab the pedal to get optimal braking...and of course that's not always easy to do, especially in an "OH $HIT" moment.

    I'm using the stock Z31 BMC...I know that a bigger BMC is needed when there isn't enough hydraulic pressure to work big calipers, and it maintains proper pressure and pedal feel...but that isn't a problem for me at all. Pedal feels good, firm not spongy, and the pressure almost seems to be too much since the fronts lock up under aggressive braking.

    I previously had the Z32 Calipers/350Z track rotors setup and don't remember ever really having this issue, although they certainly didn't brake as well as my current setup.

    My tires are Nitto NT05 with treadwear 200 so they aren't super soft compound, but not certainly not hard either.

    The obvious answer is that there's simply too much front caliper compared to the back?

    Should I consider a proportioning valve? Or would Z32 17/16 BMC help address that?

    Thanks in Advance

  • #2
    I would say you should upgrade the rear to get more braking power there to even things up. Going with a 6 piston in front was probably a bit overkill. I haven't read all of it, but this thread may help you. http://www.nissanroadracing.com/showthread.php?t=2781
    Prius... because Pretentious wouldn't fit across the back of the car...

    Cheap, Fast, Reliable - pick any two

    My 1986 Turbo Build

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    • #3
      Overkill? What's that?? lol

      I'm a firm believer in it's always better to have too much than not enough!


      But thank you, great info in that thread...good read.

      Sounds like my first step should be to change the rear pads to something a little more aggressive...it might just be that simple.

      Thanks again much appreciated.

      Comment


      • #4
        You have too much pressure and probably a long pedal. What was the piston area change from the previous setup?

        Most likely going to the larger M/C will improve the issue. It will move more fluid in the stroke but have less line pressure at the caliper. So, your pedal will feel taller/firmer but require more leg effort to lock up the brakes.
        ________________
        1987 Chumpcar

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        • #5
          Originally posted by Bremsen
          You have too much pressure and probably a long pedal. What was the piston area change from the previous setup?
          Actually the pedal feels fine...just like stock.

          The piston area now, according to Wilwood, is 4.04...I'm not sure what the Z32 Caliper area is honestly.

          Originally posted by Bremsen
          Most likely going to the larger M/C will improve the issue. It will move more fluid in the stroke but have less line pressure at the caliper. So, your pedal will feel taller/firmer but require more leg effort to lock up the brakes.
          Interesting...makes sense...however I read in another thread that the Z32 BMC would increase front bias.

          Comment


          • #6
            Not really a bias problem, but a pad compound issue. Step up to a more aggressive rear pad.

            I have 17/16" BMC, cheapest of the cheap Centric front pads for my front Z32 30mm setup, and more aggressive "ceramic-performance" on stock rears. The rears lock up first on very hard panic stops and moderate trail braking. My more spirited drives I swap out the fronts to more aggressive front pads and the fronts will lock up pretty quickly on moderate-to-heavy braking.

            1986 300ZX Turbo...sold
            1990 Skyline GT-R...new money pit
            2014 Juke Nismo RS 6-speed...daily

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            • #7
              The calipers are what shift the bias in this situation. You've altered the difference between the front piston area and the rear piston area, but kept the hydraulic side, therefore you've altered the brake bias. The master cylinder changes the pedal stroke and the caliper pressure, but since its a single bore master the front and rear circuits are changed equally. The only way to change the brake bias via the master cylinders is to run a dual master setup on a pedal box.
              ________________
              1987 Chumpcar

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              • #8
                4.04 square inches of piston area? That would be rather small...

                http://brakepower.com/help_abc_27_PAC_t.htm

                My BBK calipers come out to 7.8 square inch... (change N to 1)

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                • #9
                  Perhaps I'm reading it wrong?

                  Billet Narrow Superlite 6 Lug Mount

                  Piston: 6 Piston Area: 4.04 Pad Volume: 3.8 Mount Description: 3.50" Lug Mount Rotor Width: 1.1 Billet Narrow Superlite 6 Lug Mount

                  PISTONS: Type: Stainless Finish Red Powder Coat Piston 1 Dia. 1.62 Piston 2 Dia. 1.12 Piston 3 Dia. 1.12 Piston 4 Dia. - MATERIAL: Aluminum FIT: Maximum Rotor Dia. 14

                  I plugged the numbers into the calculator and got the same - 4.04


                  http://www.wilwood.com/Calipers/Cali...dth=&pistarea=

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                  • #10
                    looks like Wilwood only calculates the 3 piston areas, I think you need to multiply that 4.04 by 2 for full-floating calipers, resulting in 8.08.
                    Butter (credit where credit is due): "You have this "gift" where you can make cooking a Hot Pocket seem like you need a certain wavelength microwave and involve brown mustard."

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                    • #11
                      Wilwood does use some pretty small pistons, and unequal size pistons for the 6-piston setups.

                      1986 300ZX Turbo...sold
                      1990 Skyline GT-R...new money pit
                      2014 Juke Nismo RS 6-speed...daily

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                      • #12
                        I've got the Wilwood 4 pistons, and doing the math myself I get 8.24, and Wilwood lists it as 4.12, so it does seem like they are only calculating half. That said, if yours really is only an area of 8.04, your issue isn't really with the BMC. I'm running a stock BMC on mine as well and under normal driving I don't have issues. If I really get on the brakes hard the front locks first, but that is expected since it has larger brakes and also a lot less traction than the rear (235 profile tires vs 275).

                        Also, I did some research prior to buying my calipers and my piston size is only a touch larger than a Z32. So at least as far as hydraulics go, it shouldn't operate much different than Z32 calipers.
                        Prius... because Pretentious wouldn't fit across the back of the car...

                        Cheap, Fast, Reliable - pick any two

                        My 1986 Turbo Build

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                        • #13
                          Originally posted by jaqattack02
                          I would say you should upgrade the rear to get more braking power there to even things up.

                          Originally posted by jaqattack02
                          I've got the Wilwood 4 pistons, and doing the math myself I get 8.24, and Wilwood lists it as 4.12, so it does seem like they are only calculating half. That said, if yours really is only an area of 8.04, your issue isn't really with the BMC. I'm running a stock BMC on mine as well and under normal driving I don't have issues. If I really get on the brakes hard the front locks first, but that is expected since it has larger brakes and also a lot less traction than the rear (235 profile tires vs 275).

                          Also, I did some research prior to buying my calipers and my piston size is only a touch larger than a Z32. So at least as far as hydraulics go, it shouldn't operate much different than Z32 calipers.
                          The Wilwood 4 pistons have more area than the 6 pistons...go figure! Your experience sounds pretty similar to mine in regards to braking reaction. I also have a similar tire disparity with 245's in the front and 275's in the rear.

                          I gave Dave at Arizona Z a call today to get his perspective and he echoed much of what you and some of the others here are saying.

                          Passing along his take:

                          - from the sound of it that the brakes are actually working just as they should and that, simply put, the front brakes are disproportionately powerful compared to the back and that, like Bremsen mentioned, that in and of itself has increased the front bias.
                          - upgrading the BMC would increase front bias
                          - He suggested upgrading the rear calipers/discs, disabling the proportioning valve built into the BMC (mentioned in the thread jaq posted link to), and implementing an external proportioning valve
                          - He asked which size BMC I had currently have. I wasn’t sure off the top of my head but I told him it was the stock Z31 and I guessed 15/16. He said that’s the size he recommends for his full front/rear BBK.

                          I started perusing proportioning valves. Google brought me to StopTech’s site where they have a technical write up on proportioning valves and list items that will increase front or rear bias:

                          Factors that will increase front bias
                          Increased front rotor diameter
                          • Increased front brake pad coefficient of friction
                          • Increased front caliper piston diameter(s)

                          • Decreased rear rotor diameter
                          • Decreased rear brake pad coefficient of friction
                          • Decreased rear caliper piston diameter(s)
                          Lower center of gravity (i.e. lowered vehicle)
                          • More weight on rear axle (i.e. loaded)
                          • Less weight on front axle
                          • Less sticky tires (lower deceleration limit)

                          Factors that will increase rear bias
                          • Increased rear rotor diameter
                          Increased rear brake pad coefficient of friction
                          • Increased rear caliper piston diameter(s)
                          • Decreased front rotor diameter
                          • Decreased front brake pad coefficient of friction
                          • Decreased front caliper piston diameter(s)
                          • Higher center of gravity (i.e. raised vehicle)
                          • Less weight on rear axle (i.e. unloaded)
                          • More weight on front axle
                          More sticky tires (higher deceleration limit)


                          Taking all of your valuable input into account, my thought process is
                          - Upgrading the rear pads to a more aggressive compound
                          - Upgrading my tires to a softer compound…currently my NT05’s have 200 treadwear. I’m looking at NT01’s (treadwear 100 and feel much stickier than that) or Toyo Proxess 888’s (treadwear 100 with a more uni-directional pattern).

                          This should be a good start in improving the bias balance by themselves until I can tackle the rear brake upgrade and proportioning valve.

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                          • #14
                            The easiest/free upgrade you can try is shimming the rear bias spring in the master cylinder until it binds, it can be a pain to do...

                            It will eliminate the regular split point that stops the rears getting additional clamping above a certain pressure

                            It's very likely that's _all_ you need to do

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                            • #15
                              My plan is to upgrade both my rear calipers and rear pad compound. I just haven't actually gotten around to doing that. Need to swap my rear control arms first, along with getting the M30 ebrake drums installed.
                              Prius... because Pretentious wouldn't fit across the back of the car...

                              Cheap, Fast, Reliable - pick any two

                              My 1986 Turbo Build

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