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

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

    A few months ago I ripped apart the whole front end and installed coilovers, ripped out the ABS, put in all new tie rods, wheel bearings, Gen 2 spindles, rotors, brake pads, and the brembo cts-v calipers. After I got everything back together I took it out for a test spin to break in the new brake pads.... The brake pedal felt super stiff as if the booster wasn't working. Got it back home, and noticed a small leak at the T junction that comes with the ABS delete kit. Tightened that back up, bled the brakes again. Took it out again, and no improvement. Hmm... I could hear a hissing sound when I pressed the brake pedal and it was slow to return, so I figure ok, the booster is shot. Ordered a new booster and a new master cylinder, because I'm already paying shipping, why not? Bench bled the master cylinder, got everything installed, and then bled the brakes for a 3rd time. The braking improved but if I jam on the pedal I still can't get the brakes to grab or lock up like they should. I figured maybe I'm not bleeding them right, so I took it to a Firestone shop my friend works at and she had the tech run through and bleed the whole system again... still no improvement. The only thing left is the proportioning valve. Unless I'm missing something? I double checked the calipers and the center of the caliper lines up perfectly with the center of the rotor... Even if one of the calipers was slightly off, you'd think it would still grab hard and pull to the side, no?

    I'm at a loss here, outside of replacing the proportioning valve, I dunno what else is left. You'd think with 3" bigger rotors and significantly more brake pad surface these things would be throwing me through the windshield... but right now they're worse than the stock brakes which were awful at best.

    Anyone installed the kit that can throw some suggestions my way?

  • #2
    I put LS1 Camaro brakes on my Sy and it felt like I could get the truck to do an endo if I wanted to.

    Is your vac booster check valve good?

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    • #3
      haha "endo" kicking out the old school BMX reference! love it! haha

      Yeah the check valve is good... that was the first thing I swapped before I started throwing money at it with a new booster and master cylinder. The new booster came with a new check valve too, so that'd be 3 check valves and no difference.

      A guy on the .net forums said he swapped his proportioning valve with one from Wilwood, but didn't mention a part number. I'm feeling like it's gotta be the proportioning valve... it's hard to explain but it almost feels like the rear brakes are grabbing first and not allowing the fronts to fully engage. I did read online that as a "safety feature" if you have a leak in your brake lines that the proportioning valve has a lil cylinder in it that will shift and force the fluid to the rear brakes if there's a leak in the front brake lines so you don't bleed out your system and you can still stop. I did have a small leak up front when i first test drove the truck, and I'm wondering if that's what happened. Might just bring it in to a legit brake shop and have them screw with it...

      The Ty is now my daily driver, so I gotta be able to stop when the soccer mom in front of me is messing with her phone and then jams on her brakes at the last second.

      I'll post an update when i get it fixed.. just for the integrity of the "search" feature.

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      • #4
        Did the system bleed easily and normally? No restricted hoses, stuff like that, right?

        How much bigger in AREA are the pistons in the new calipers compared to the OEM's? How low does the pedal travel? Is it possible that you're using the full stroke of the master cyl and are bottoming the front section, and then all you have is the rear brakes? Compute the difference in displacement between the two calipers. That could be it right there.

        If you still have rear drum brakes, leave the combination valve as-is for now. You need the residiual-pressure portion of it with drums. When you upgrade the rears to disc, you can do the combo valve mods.

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        • #5
          Originally posted by DaveP View Post
          Did the system bleed easily and normally? No restricted hoses, stuff like that, right?

          How much bigger in AREA are the pistons in the new calipers compared to the OEM's? How low does the pedal travel? Is it possible that you're using the full stroke of the master cyl and are bottoming the front section, and then all you have is the rear brakes? Compute the difference in displacement between the two calipers. That could be it right there.

          If you still have rear drum brakes, leave the combination valve as-is for now. You need the residiual-pressure portion of it with drums. When you upgrade the rears to disc, you can do the combo valve mods.
          Hey Dave, thanks for the response... I only swapped out the front calipers with new Brembo 4 piston calipers aka CTS-v Rear brakes (haven't done the rears yet)... After swapping out the booster and master cylinder the pedal now feels "normal"... it doesn't go to the floor, and it gets a lil past half way, maybe 3/4 before it feels like it "stops". When I apply more force to the pedal, the fronts don't grab/lock up like they should, and it feels like any additional pressure is going to the drums. I'm sure there's quite a difference in displacement now with considerably larger calipers up front, but is the stock prop valve even adjustable to compensate for the displacement difference?

          Sorry, I'm super novice when it comes to brakes, and this is all uncharted territory for me.

          Thanks for any insight.

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          • #6
            Originally posted by Typhoon0627 View Post

            it doesn't go to the floor, and it gets a lil past half way, maybe 3/4 before it feels like it "stops". When I apply more force to the pedal, the fronts don't grab/lock up like they should, and it feels like any additional pressure is going to the drums.
            I think I was on the right track in my first post. The displacement of the 8 caliper pistons exceeds the displacement of the master cyl to feed them. The front brake portion of the M/C bottoms, and only the rear brakes are being applied.Compute the displacement of both the OEM and the new calipers. You'll have to measure the diameter of the pistons, or find the spec somewhere. Area of a circle is Pi X radius squared. For the Brembos, multiply this area times 4. (The number of pistons per caliper). I'm not sure what the max area for calipers for the stock 1" M/C is. If the Brembo area is more than twice the area of the OEM, this may be it. Do the math, and post back with your findings. There are several remedies. It will be easier to focus if we know that this IS the problem.

            Another "test" for diagnosis is can you improve the front braking by "pumping-up the pedal" during a stop? (Don't come all the way to the top of the pedal stroke, just little pump-ups). If = YES, this hints that the M/C volume isn't enough.

            EDIT II: Do a little research, and find out the M/Cyl diameter of the Cadillac that these calipers are used on OEM. The SyTy M/C is 1". I suspect the Cadillac is larger. More volume. If = YES, don't jump in and order a different M/C. There's a LOT more to this. I suggest this to confirm what I think the problem is.

            I still don't think the combination valve has anything to do with the root problem. If anything, you'll need more pressure reduction to the fronts because of the increased front braking from the bigger rotor diameter. Proportioning imbalances are masked in a SyTy because of the AWD. With all wheels mechanically linked, it is difficult to lock up just one wheel. Again, I suggest saving combination valve mods and final front-rear balance tuning until you finish the rears. AND figure out why the fronts aren't "working".

            You'll get it.
            Last edited by DaveP; 12-08-2018, 02:46 PM.

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            • #7
              Thanks for the info Dave! I'll have to dig into this...

              The weird part is, in all the threads I read on .net about these calipers, it was stated that the stock MC was plenty sufficient, and I never saw anyone post about any problems after the install. All the follow ups I saw were to the tune of "way better than stock! blah blah blah", nothing about the probs I'm having... which is making me think it's a "me" problem and something I did wrong in the install vs any mechanical inefficiencies.

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              • #8
                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.

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                • #9
                  Hey Dave, these are the calipers I have... https://www.amazon.com/dp/B000S2Q5O0..._t2_B000S2OR8Q
                  As i mentioned before, I'm a total novice when it comes to brakes outside of bleeding, replacing pads, rotors, and calipers... But could it be something totally stupid and simple as popping the drum off and backing off the pad adjuster a bit? I know the drums self adjust to compensate for pad wear, but if I had a small leak in the front brake lines, could the rears have self adjusted to compensate for that? I'd think if they did, it would feel like I was driving with the e-brake on... but if it's not that, or an issue with the combination valve... I doubt i'd have 2 defective calipers, and I don't think glazed pads would be this bad...
                  Last edited by Typhoon0627; 12-11-2018, 08:45 PM.

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                  • #10
                    If I'm reading that correctly you're using the CTS-V *Rear* caliper on the front? I don't think those are the numbers Dave used.



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                    • #11
                      Originally posted by RealFastV6 View Post
                      If I'm reading that correctly you're using the CTS-V *Rear* caliper on the front? I don't think those are the numbers Dave used.
                      I probably didn't use the correct caliper piston dimensions. I may have used dimensions for FRONT calipers.

                      Most modern brake systems designed for use with ABS are pretty well balanced without the use of proportioning valves. Any imbalance that results in undesirable wheel lock-up is handled by the ABS. So, if the dimensions I used for the calipers are for FRONT calipers, the rear calipers used with those fronts will have smaller piston area. Too small area results in reduced braking effort, because the ratio goes DOWN numerically..

                      Braking force at the calipers is a mathematical ratio between the area of the master cyl and the area of the calipers. Think of a rear axle ratio. The higher the number numerically, the greater the input force is multiplied. A pedal ratio of 2:1 will require twice the foot pressure of a 4:1 for the same force on the pads, all else being equal.

                      I still do not think the rear brakes have anything to do with the "won't stop" issue. I don't think the fronts are working very well, and rear brakes aren't very efficient at stopping the car by themselves.

                      One other possibility is you have a bad master cyl. There is a "quick take-up" section in the master cyl for the front brakes. If this section is bypassing, the pedal will be low, and may not have enough volume from there to fill the new calipers before it bottoms. The quick take-up portion of the MC has been an issue in the cars it is used in for decades. When I did my Ty's 2nd Gen conversion (front and rears) I also replaced the MC with the 2nd gen version mostly to get rid of that damned quick take-up deal. The best p[art of my Ty is its brakes. The pedal effort is about 2/3 of what it was stock. It's been 2 years and about 20,000 miles since I did the conversion; I've enjoyed every brake application since.


                      Take a front wheel off and MEASURE the diameter of the caliper pistons. Even if you just get close enough by looking through the inspection hole in the caliper. Let's stop guessing, and figure this out.

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                      • #12
                        I don't even have to take the wheel off... I've got 2 more of the exact same calipers in the garage. I'll grab one in the morning and bring it in to work... should be able to get an accurate measurement of the calipers with some calipers! Man... I wish I knew about the 2nd gen MC, I just replaced mine with this one... https://www.rockauto.com/en/moreinfo...297578&jsn=481

                        stay tuned!

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                        • #13
                          Ok, well the guy at my work with the calipers isn't here today and i dunno where he keeps them... So if I'm eyeballing it with a tape measure correctly, the 2 upper (right in pic) pistons are 1 1/2", and the 2 lower pistons (left in pic) are 1 5/8". This is measuring from the outside edge of the black ring. You can see the size difference here...
                          Last edited by Typhoon0627; 12-18-2018, 08:35 PM.

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                          • #14
                            You don't measure the black, you just measure the outer diameter of the piston. Looking online it looks like you've got 28mm and 32mm pistons. Your effective caliper clamping area is something like 2.1" at the caliper, divided by a M\C area of .7" for a 3:1 braking force ratio. (Use Dave's math to double check)

                            When I posted earlier, I was actually just a little surprised that using the rear CTS-V calipers was even "a thing." I just assumed from the start you were talking about the big bad ass fronts. For reference, stock brake ratio is in the neighborhood of 7:1, and LS1 Calipers with the stock M\C is still something like 6.75:1, but keep in mind the pads are massive compared to stock and on a larger disc.

                            Switching to a 7/8 bore MC or even smaller will increase the ratio if you're married to those calipers.
                            Last edited by RealFastV6; 12-19-2018, 09:46 PM. Reason: ...because your MC isn't 1", it's 24mm... thanks a lot Bin Laden.

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                            • #15
                              Originally posted by RealFastV6 View Post
                              You don't measure the black, you just measure the outer diameter of the piston. Looking online it looks like you've got 28mm and 32mm pistons. Your effective caliper clamping area is something like 2.1" at the caliper, divided by a M\C area of .7" for a 3:1 braking force ratio. (Use Dave's math to double check)

                              When I posted earlier, I was actually just a little surprised that using the rear CTS-V calipers was even "a thing." I just assumed from the start you were talking about the big bad ass fronts. For reference, stock brake ratio is in the neighborhood of 7:1, and LS1 Calipers with the stock M\C is still something like 6.75:1, but keep in mind the pads are massive compared to stock and on a larger disc.

                              Switching to a 7/8 bore MC or even smaller will increase the ratio if you're married to those calipers.
                              Thanks for correcting my error on the pistons... you'll have to pardon my ignorance. I couldn't find the piston size online for the fronts or the rears, not even on brembo's site. Where did you find the size info?

                              Anyway, to say this is aggravating, is an understatement....

                              Back when the kits were being designed to adapt these calipers for our trucks it was stated that you needed at least 18" wheels to use the front CTS-v calipers. If you had 17's you had to use the rear CTS-v calipers. It was also said that regardless of front or rear CTS-v's, the stock MC and proportioning valve would work just fine with no need to modify anything.

                              At the time, I had 17" wheels, and Amazon was practically giving away the rear calipers at $77/ea. So I got 4 calipers, 4 discs, pads, and an ABS delete kit to do the conversion, when I had the time. 5 and half years later (don't judge me!), I buy the front brake bracket kit from Sportmachines (which came with an extremely thorough set of directions, oh wait...), I pop the ABS out, get the front brakes installed, and I've been chasing this issue ever since... Technically you could say the stock MC works "in theory" because the truck in fact does stop... it just doesn't stop well, or not as well as it should for having giant calipers and rotors. This is just another instance of bad intel on $yTy.net, among many others, where people claim to know WTF they're talking about, without having thoroughly vetted the application.

                              Unfortunately, I'll have to say I am married to these calipers since it would cost me far more to buy another bracket kit, new calipers, new rotors, and new pads just to adapt the fronts... versus tracking down a new master cylinder that works. Besides, the surface area of the front calipers on the CTS-v can't be THAT much bigger, right? The rotors themselves are 13.5", and I believe the fronts are 14.1"... just over half an inch may matter to some women, but when it comes to braking... I don't think you'd feel THAT much of a difference haha.

                              Jokes and rants aside... The stock MC is 24mm, and the Gen2 that Dave swtiched to is 25.4mm or 1", and the bore on the 2006 CTS-v is 1"... so... ya got me...
                              Last edited by Typhoon0627; 12-21-2018, 12:13 PM.

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