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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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