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CTS-v Brake upgrade not so much of an upgrade?

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  • #16
    I read that Real Fast came up with a 3:1 ratio, and I thought "well F uk, there's the problem! EDIT 1/11: He's right. The force rqtio is way too low.
    Total piston area = 2838 mm sq. Divide by 452 mm sq for the stock 24 mm sq Master Cyl is a 6.28 ratio. RIGHT NOW you have 3.14 Ratio.

    I converted my 2-3/8" for the stock caliper to 60 mm, and came up with 2856 mm sq. Divide by 452 for the stock M/C = 6.32. STOCK is 6.32 Ratio


    Remove the proportioning section of the stock Combination Valve. This is the side on the FRONT brakes lines.
    Remove the nut.
    Remove the plunger and spring.
    Remove the seal from the plunger. (So the valve doesn't "work" anymore)
    You have to plug the little hole in the nut to seal it. You can tap it, and put a screw in it with red loc-tite. I tig welded the hole closed. More quicker.
    Put the guts back in the combo valve in the order they were, and install the nut.

    You have to leave the spring and plunger in there to center the valve plunger for the warning light section. When you do the rear discs, you'll remove the rear side of the combo valve, and grind the land off so the rear section doesn't work either. But for now, with rear drums leave the rear section intact.
    Last edited by DaveP; 01-11-2019, 10:41 PM. Reason: Removed erronious info I had because I was wrong about computing force ratios.

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    • #17
      It was only one side of the Caliper, but that was on purpose.

      Think about it this way...

      If you have a sliding caliper and it has a single piston (like our stock brakes) or even dual pistons like a Camaro caliper, then the brake force is going to slide the caliper on the pins equal to the amount of force exerted on the pad that it's actually pushing against, leaving you half the force of the piston caliper. The other half of the force is being transmitted through the pins to the other side of the caliper to the second pad. In other words, yes it's a single piston, but it's really pushing on two pads simultaneously.

      For a fixed caliper that's not happening. You're getting the force of each piston on each pad, with twice the number of pistons, but the result is still the same.

      If you have a 4 piston fixed caliper with 4 x 1.5" pistons, or a 2 piston floating caliper with 2 x 1.5" pistons, the piston area is theoretically the same.

      So when calculating piston area for the purposes of brake ratio, you can ignore the second side of the caliper.

      I think I used 2.5 for our stock caliper so that explains the math difference.
      Last edited by RealFastV6; 12-22-2018, 10:03 AM.

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      • #18
        Originally posted by RealFastV6 View Post
        It was only one side of the Caliper, but that was on purpose.
        Think about it this way................
        So when calculating piston area for the purposes of brake ratio, you can ignore the second side of the caliper.
        1/11/2018: EDIT: I removed a lot of text here where I was mistaken, and incorrect. Mostly to remove confusion if anyone stumbles on this thread in the future. Jump to the end to see where I acknowledge being wrong. I'm not hiding anything,

        `````````````````````````````````````````````````` `````````````````````````````````````
        Have someone press on the pedal while you watch and feel the caliper with your hand. If the caliper "rocks" or has any noticable movement before the pedal gets firm, stuff is moving, and volume is being consumed before the force is applied to the pads.

        Another check is look at the rotor surface for the wear. If pads are not contacting the rotor surface evenly on both sides, inside to outside, this is another indication the caliper is "cocked" to the rotor, and there is compliance.

        Ok, I gotta' run. I'll check in this evening.
        Last edited by DaveP; 01-11-2019, 10:47 PM.

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        • #19
          I don't have my whiteboard, so let's just say we do an apples to apples comparison where 100psi comes into each caliper after take-up.

          Caliper 1 is a single 2.375" piston sliding caliper. (stock caliper)
          Caliper 2 is a sliding dual 1.8" piston caliper (LS1)
          Caliper 3 is a fixed caliper with 2.375" single pistons on each side. (I made this up - I don't know that it exists)
          Caliper 4 is a fixed dual piston caliper with dual 1.7" pistons on each side. (I also made this up)
          Caliper 5 is a fixed dual piston caliper with dual 1.185" pistons on each side. (Close to OP calipers)

          Caliper 1 - After take-up, the single piston gets all 100psi. The single 2.375" piston has an area of 4.430". The piston imparts half the force (220lbs) on the inside pad, and half the force (220lbs) on the outside pad. The resulting clamping force at 100psi is 440 lbs.

          Caliper 2 - After take-up, the caliper balances the pressure between two cylinders that have an area of 2.5" each. Working together, half the force of each piston is imparted on the inside pad, and half on the outside pad. The resulting clamping force at 100psi is 500 lbs.

          Caliper 3 - After take-up, the caliper balances that pressure among all the available pistons hydraulically, which in this case is just two. The pistons still have an area of 4.430" each, and impart the full available force (220lbs) on their respective pad. The resulting clamping force at 100psi is 440 lbs.

          Caliper 4 - After take-up, the caliper balances that 100psi off to four pistons. The pistons have an area of 2.2" each, and impart the full available force (2.2" area * 25 psi = 55lbs), times 4 total pistons, for a resulting clamping force of... 440lbs. Still 220lbs on each pad.

          Caliper 5 - After take-up, the caliper balances the same 100psi off to four pistons. The pistons have an area of 1.103" for a clamping force of 27.5lbs each, times 4 total pistons, for a total resulting clamping force of only 110lbs. This is only 55lbs of clamping force per pad. The pistons are anemic. You'll need to build up more pressure in the master cylinder than you are currently comfortably able to do with a 24mm or 1" master cylinder.

          The brake ratios for the above with a 24mm MC would then be...

          Caliper 1 - 1:6.318
          Caliper 2 - 1:7.258
          Caliper 3 - 1:6.318
          Caliper 4 - 1:6.318
          Caliper 5 - 1:3.146

          ...which intuitively makes sense to me based on the resulting clamping force.
          Last edited by RealFastV6; 12-22-2018, 10:17 PM.

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          • #20
            I'm not going to check all the math for 5 caliper scenarios. But I NEVER used the term "Pounds Per Square Inch". I used, and MEANT, "FORCE". Ie, the foot pressure on the M/C input rodl, multiplied by the total piston area divided by the M/C area = 100 pounds of force at the piston(s)... Not "psi" behind the piston(s)..

            I used two configurations. A single piston with an area that produces 100# of FORCE. And an opposing two piston configuration where each piston produces 50# of FORCE with the same foot pedal input. 50+50 = 100.

            M/C = 1 in sq, and single piston with 3 in sq is a 3:1 ratio. Put 33.3# on M/C push-rod, and you will have 100# of force at the piston.
            M/C = 1 in sq, and single piston with 1.5 sq in is a 1.5:1 ratio. With 33# on the M/C push-rod, you will have 50# (49.95) of force at the piston. But there are TWO pistons. 50+50 = 100.

            It doesn't matter how many pistons there are. It doesn't matter what the pressure in the line is. What matters is the ratio between the area of the M/C devided into the total AREA of ALL the pistons.

            Having put hours into this now, I'm confident that the OP does not have a force ratio issue, as long as the dimensions of 28mm and 32mm I used for the CTS-v calipers are indeed accurate. The OEM and his 4-piston calipers are virtually the same area. And this swap has been around for quite awhile. If there WAS a ratio problem with these calipers, one would think it would have been uncovered years ago. Not be uncovered for the first time now.

            I've made a couple of suggestions as to where to look for the issue. Combo valve proportioning valve, and compliance in the mounting bracket that has the caliper cocked to the plane of the rotor.
            Last edited by DaveP; 12-23-2018, 12:19 AM.

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            • #21
              Ok. If the M/C AREA is 1 in sq, then 100 pounds of input = 100Pounds Per Square Inch. So I suppose we can use 100 PSI as the constant for all 5 caliper configurations.. I've put my remarks in BOLD.

              Originally posted by RealFastV6 View Post
              Caliper 1 - After take-up, the single piston gets all 100psi. The single 2.375" piston has an area of 4.430". The piston imparts half the force (220lbs) on the inside pad, and half the force (220lbs) on the outside pad. The resulting clamping force at 100psi is 440 lbs.
              ^^Correct. 100psi behind 4.43 in sq is 443 pounds of force in psi,. 1 x 443 = 443, 221.5 per pad. ^^

              Caliper 2 - After take-up, the caliper balances the pressure between two cylinders that have an area of 2.5" each. Working together, half the force of each piston is imparted on the inside pad, and half on the outside pad. The resulting clamping force at 100psi is 500 lbs.
              ^^Correct 100psi behind 2.5 in sq is 250 psi. 2 X 250 is 500psi, 250 per pad/.^^

              Caliper 3 - After take-up, the caliper balances that pressure among all the available pistons hydraulically, which in this case is just two. The pistons still have an area of 4.430" each, and impart the full available force (220lbs) on their respective pad. The resulting clamping force at 100psi is 440 lbs.
              ^^No. 100psai behind 4.43 in sq is 443 psi. 2 X 443 per pistons is 886psi, 443 per pad.^^.

              Caliper 4 - After take-up, the caliper balances that 100psi off to four pistons. The pistons have an area of 2.2" each, and impart the full available force (2.2" area * 25 psi = 55lbs), times 4 total pistons, for a resulting clamping force of... 440lbs. Still 220lbs on each pad.
              ^^No. 100psi behind 2.2 in SQ is 220 psi. 4 X 220 is 880 pounds of force, 440 per pad.^^

              Caliper 5 - After take-up, the caliper balances the same 100psi off to four pistons. The pistons have an area of 1.103" for a clamping force of 27.5lbs each, times 4 total pistons, for a total resulting clamping force of only 110lbs. This is only 55lbs of clamping force per pad.
              ^^No. 100psi behind 1.103 is 110.3 PSI. 4 X 110.3 is 441.2 pounds of force, 220.6 pounds per pad.^^

              Your error is to be dividing the input pressure by the number of pistons. This is not correct. Pressure is pressure. Pressure must be equal anywhere in the system, in all directions. If the input IN TO the M/C is 100pounds, and the area of the M/C is 1 in sq,, the line pressure WILL be 100 psi. Period. It doesn't matter if there are 1 or 1,000 pistons. It is the area of each piston, added together, times the force in psi behind them that is the force applied to the rotor.

              If the input pressure is he same, it is STILL input pressure x the total piston area. Divide by the two pads if you wish, I just use total force on the rotor from both sides. Fixed or sliding does NOT make any difference to force ratio between the M/C and caliper piston area.

              Caliper #1 (stock) and caliper #5 (close representation of the CTS-v) create the same force on the pads, because the total area of the two calipers are the same.

              Cheers. And Merry Christmas.
              Last edited by DaveP; 12-23-2018, 01:59 AM.

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              • #22
                Hahaha guys... thank you! I definitely wasn't expecting this level of deep dive analysis of brake calipers and how it all works! I appreciate it more than you know, especially since I actually learned something! A lot of times when I don't know how to do something or figure something out, I'll ask for help or troubleshooting suggestions... and if i can use an analogy for a second... if I ask what's 12x12?... I'd rather someone show me how to get the answer, instead of just saying 144. So again, thank you!

                So I did a lil recon of my own as well... not to the mathematical level you guys did, but just to make sure I'm not crazy. I was out with a friend of mine, and we happened to run into a guy he does work with from time to time who coincidentally has a 2006 CTS-v... I got to talking to him, and he was nice enough to let me test his brakes in the parking lot. Granted he has 4-wheel discs, but they grab as you would expect. I let him test my Ty, and even he agreed they definitely don't feel right.

                I'm gonna pop the wheels off tomorrow and double check the alignment of the calipers to the rotor, and check for movement when pressing the pedal. When I bolted everything up I put the rotor on and tightened the lugs to hold the rotor in place, then aligned the caliper, bolted it up, and then double checked to make sure they weren't crooked.

                Prior to this whole venture, I was pretty used to the brakes on my daily driver which would stop on a dime with about the same amount of force required to press the gas pedal. Any time I'd get in the Ty, I'd think good god... these brakes are horrible! Cause I'd practically have to stand on the pedal to get the truck to stop. I didn't remember my Syclone being THAT bad, but again, I figured ahhh I'm just used to my daily and this is how brakes were 27 years ago. But after installing the cts-v's and seeing only a minor improvement, I'm convinced there's something wrong.

                We've ruled out the MC volume isn't a problem after all, and I've replaced the MC and the booster, so that rules those out... I'll check the caliper alignment again, but I'm not sure that's the problem either, only because when I do hit the brakes, the truck doesn't pull in either direction. I don't think I could've equally cocked both calipers? I've only put a few hundred miles on the truck since I put the brakes on, so even if I popped the calipers off and had a look at the pads, I don't know I'd see any telltale signs of wear. Would a kink in the hard lines that run over to the pass side cause this??? If not, all that's left is the valve. Dave, I'll try taking it apart and doing what you said. Although, I'm not sure I'll have a chance to get to it with Christmas in a couple days, and then I'll be out of town for new years... So feel free to take a few days off from this haha.

                Dave, if I ever happen to run into you at a SoCal gathering after all these years, beer n food is on me! RealFastV6, not sure when I'll be out in CT again, but I'd do my best to track down some Heady Topper for ya (if you're a craft beer guy), either way... thanks for the info and the help!

                Have a merry Christmas and a great new years! Cheers!
                Last edited by Typhoon0627; 12-23-2018, 05:13 AM.

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                • #23
                  Well Dave you should get comfortable and pull up a chair, because you don't need to convince me, you need to convince the entire brake industry.

                  https://www.wilwood.com/TechTip/TechCaliperTip

                  Caliper Piston Area

                  A calipers piston area is calculated by finding the total piston area from one side of the caliper (this is true for a single piston caliper also). The graph provides the piston area for individual piston diameters. Note that differential piston bore calipers will be the total piston area of the different size pistons.
                  http://www.outlawdiscbrakes.com/faq.html

                  Calculating the Square Inches of Caliper Piston Area
                  Pi times (radius of the piston squared) times (half the number of pistons).

                  Example:
                  Calculate the square inches of piston area of a caliper with four pistons 1.75" each.
                  Pi=3.1417
                  Radius of a 1.75" piston = .875"
                  3.1417 x (.875 x .875) x 2 = 4.81 sq./in. of piston area
                  http://www.tceperformanceproducts.com/bias-calculator/

                  Note: multi piston calipers express their values using one HALF of the caliper body. This accounts for the floating aspect of the single piston caliper. A six pot caliper would be 1.625/1.125/1.125" for example. True clamping force would be double that but also double the single piston of a floating caliper taking into account the 'pull' of the outer pad to the rotor surface. Using total area (all six for example) would require you double that of the floating caliper also- thus the net result is the same whichever way you do it.
                  https://www.onallcylinders.com/2017/...ke-pedal-woes/

                  For the sake of explanation, let’s change the caliper to a fixed four-piston caliper. For opposing piston calipers, we only use one side for the calculation, so in this case we will find the area of the two pistons.
                  It's obvious my understanding of "why" isn't concrete, but "calculate one side of the brake caliper" is accepted math univerally in the industry.

                  Would it be that on a sliding piston caliper the single piston is really acting as two pistons? What are we missing?

                  I'm not convinced at all based on anecdotal evidence that other people are using these calipers - because I don't think they are. I didn't even know this was a possible upgrade. I think most people that are using CTS-V Calipers are using the much larger Fronts - which, btw, don't seem to require a different master cylinder, which dispenses with the master cylinder volume argument pretty quickly.

                  Comment


                  • #24
                    Agree on the PSI - even as I was laying it out, I started to question myself when I got to that point. I think the fly in the ointment will end up being something like "the piston in a single piston sliding caliper is actually two pistons, one on each side." The thought being that an apples to apples comparison can be had either by doubling the area of the single piston, or halving the area of fixed pistons.

                    I think this will end up being the correct math.

                    This is at 100psi after take-up.

                    Caliper 1 is a single 2.375" piston sliding caliper. (stock caliper)
                    Caliper 2 is a sliding dual 1.8" piston caliper (LS1)
                    Caliper 3 is a fixed caliper with 2.375" single pistons on each side. (I made this up - I don't know that it exists)
                    Caliper 4 is a fixed dual piston caliper with dual 1.7" pistons on each side. (I also made this up)
                    Caliper 5 is a fixed dual piston caliper with dual 1.185" pistons on each side. (Close to OP calipers)

                    Caliper 1 - The single 2.375" piston has an area of 4.430". The resulting clamping force at 100psi is 443 lbs.
                    Caliper 2 - The Pistons have an area of 2.5" each. The resulting clamping force at 100psi is 500 lbs.
                    Caliper 3 - Dual fixed pistons with an area of 4.430", resulting clamping force at 100psi is 443 lbs.
                    Caliper 4 - Quad Fixed Pistons with an area of 2.2" each, resulting in 443lbs. Still 221 lbs on each pad.
                    Caliper 5 - Quad Fixed Pistons with an area of 2.206" for a clamping force of 220lbs total.

                    The brake ratios for the above with a 24mm MC would then be...

                    Caliper 1 - 1:6.318
                    Caliper 2 - 1:7.258
                    Caliper 3 - 1:6.318
                    Caliper 4 - 1:6.318
                    Caliper 5 - 1:3.146
                    Last edited by RealFastV6; 12-23-2018, 11:57 PM.

                    Comment


                    • #25
                      Originally posted by RealFastV6 View Post
                      I'm not convinced at all based on anecdotal evidence that other people are using these calipers - because I don't think they are. I didn't even know this was a possible upgrade. I think most people that are using CTS-V Calipers are using the much larger Fronts - which, btw, don't seem to require a different master cylinder, which dispenses with the master cylinder volume argument pretty quickly.
                      Here's the page on the Sportmachines site... http://www.sportmachines.net/store/drivetrain/rf-front-brake-bracket-kits.html, I have the CTS-v Small Front kit.

                      I was up til 3 last night going through pages and pages of old threads about these kits, and found a post where someone using the CTS rears up front said they had to get an adjustable proportioning valve to compensate line bias... err something like that? But fail to mention of which valve they used. I came across another thread where someone said they're using a wilwood proportioning valve, but no mention of which one. After looking at the Wilwood site, this looks like the only combination proportion valve they have, so it must be this one? https://www.summitracing.com/parts/w...5048/overview/

                      Wouldn't Dave's mod of the stock valve achieve the same thing, sans variable pressure adjustment?

                      Comment


                      • #26
                        I don't understand how you come up with the clamp force of caliper #3 being the same as caliper #1. Caliper#3 has TWO pistons. It produces TWICE the clamping force. Yet you still cite the force of the two calipers as being the same. Where is the force of the second piston going? Disneyland?

                        I'm out. I'm not a brake engineer. I'm done arguing for 5 f-in days. There's no learning taking place. My 2nd Gen brakes work great and cost me less than $800 all-in, so there's no impetuous for me to solve this.. I'm out of ideas. Have a Merry Christmas.

                        Comment


                        • #27
                          Originally posted by DaveP View Post
                          I don't understand how you come up with the clamp force of caliper #3 being the same as caliper #1. Caliper#3 has TWO pistons. It produces TWICE the clamping force. Yet you still cite the force of the two calipers as being the same. Where is the force of the second piston going? Disneyland?
                          All else being equal, why would the one on the right create twice the force as the one on the left?

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                          • #28
                            I'll try Dave's valve trick and report back with results...

                            Just for knowledge sake, and because now I'm confused....
                            If the clamp force of a 4 piston caliper is equal to that of a stock caliper, then what's the advantage of going with 4 piston or even 6 piston calipers? I can't imagine all of the increased braking performance coming from just a larger surface area of the pads and rotors, can it?

                            I have to admit, long before this thread and any knowledge of piston diameters and relative pounds of clamping force... I thought each piston provided an equal amount of clamp force... meaning 4pistons provided twice as much clamp force as 2 piston calipers... that's over generalizing without getting into piston diameters and all that. But I was always under the impression that the bigger calipers with more pistons were applying significantly more clamping force in addition to the surface area and that's how the brakes were able to perform so well over our stock brakes. If that's not the case, and these calipers exert the same amount of clamp force as stock calipers, then this brake "upgrade" is merely for looks instead of performance.

                            Comment


                            • #29
                              Originally posted by Typhoon0627 View Post
                              I'll try Dave's valve trick and report back with results...

                              Just for knowledge sake, and because now I'm confused....
                              If the clamp force of a 4 piston caliper is equal to that of a stock caliper, then what's the advantage of going with 4 piston or even 6 piston calipers? I can't imagine all of the increased braking performance coming from just a larger surface area of the pads and rotors, can it?

                              I have to admit, long before this thread and any knowledge of piston diameters and relative pounds of clamping force... I thought each piston provided an equal amount of clamp force... meaning 4pistons provided twice as much clamp force as 2 piston calipers... that's over generalizing without getting into piston diameters and all that. But I was always under the impression that the bigger calipers with more pistons were applying significantly more clamping force in addition to the surface area and that's how the brakes were able to perform so well over our stock brakes. If that's not the case, and these calipers exert the same amount of clamp force as stock calipers, then this brake "upgrade" is merely for looks instead of performance.
                              More bigger pistons will give you more clamping force, but that's not what you have. You have more VERY small pistons (the actual measurable area of which total up to less than the single OEM brake piston), and therefore a master cylinder that isn't sized to provide enough pressure for them to work. The CTS-V fronts that match your rears for instance have twice the clamping force.

                              4 Piston Calipers typically have a bunch of other reasons why they're better than a single piston sliding caliper, including larger pads, larger rotors, more consistent pressure across the pad (especially with different piston sizes), which is why I suspect that your brakes are even as good as they are. You're starting with half the clamping force, but everything else is pretty ideal compared to the stock brakes.

                              The combination valve mod that Dave laid out removes the minor delay associated with the front brakes to give the rear brakes time to physically engage. I don't know that it's going to help but it's worthwhile to do anyways when you swap to rear discs so it's worth a shot now - although it means you'll need to bleed the brakes again.

                              Who has done the CTS-V Rears as Fronts modification successfully? I ask because I searched and didn't find it on the other forum.

                              Last but not least here's another thought that doesn't involve a ton of work or money or guesswork...

                              You could get a brake pressure gauge. They screw in place into the bleeder screw on the caliper. Wilwood and others make them. Find out how much brake pressure you're actually getting at the caliper. This is going to tell you really quickly whether something is wrong outside of your caliper selection. If you're only getting something like 400psi at the caliper with the engine running and you pushing down on the brakes hard, well then something is wrong in the MC\Combo Valve that is limiting your pressure to the caliper. If you're getting the full (1000+) psi with appropriate pedal pressure, then you now know it's your caliper selection or possibly the setup against the rotor.
                              Last edited by RealFastV6; 12-24-2018, 06:44 PM.

                              Comment


                              • #30
                                Originally posted by DaveP View Post
                                I was curious enough to measure a stock caliper and then go online and find what I think is the correct Brembo caliper. The stock caliper is 4.704 InSq and the Brembo I think it is is 42MM which works out to 4.66 InSq for the 4 pistons. No real difference. So piston area isn't your problem afterall.

                                I'll think about it some more.
                                Yes, that's correct. A 4 piston Brembo Caliper with 42MM pistons is 4.66 inSq.



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