CPP rear big brake kit with e-brake: An investigative report

[gator68428]

(two weeks ago)
I have had the CPP big brake kit (front and rear) on my 68 Firebird for a few years now and thought it worked pretty well until I took the car to the track and realized the rears were not participating that much. I just changed to a 1" bore Wilwood master cylinder with rear prop valve. With prop valve wide open I still wasn't able to get the rears to lock up under hard braking. So I have no clue how much the rears were participating... Was hoping to get the rears to lock up then dial them back with prop valve... Yes i squeezed the e brake several times and bled the system properly.

Here is some video from the track. You can see the front tire smoke (at 1:35 and few more times after). Flat spotted the front tires pretty bad as a result (this is what lead to the Wilwood master with prop valve)
https://youtu.be/11HKzq5kHlo

Now tired of the cast iron front truck calipers with limited pad selection, I just upgraded to Kore3 C6 Z06 front kit and may have to go with a rear kit from him as well.

(yesterday)
But, in the interest of saving $$, I decided to devote one more day to trying to get the CPP rear brakes to function properly. I bought a pressure gauge to mount in the bleeder screw port to help (Tobin's recommendation). I have the 1"bore Wilwood master with cast dual reservoirs and rear prop valve kit (Willwood). Power brakes.

Full disclosure: I did not have the e-brake hooked up before two weeks ago (directions say you need to). But I did use channel lock pliers to squeeze the lever several times before my previous tests where I determined they weren't working properly. So, yesterday I hooked the e-brake back up and inspected its operation. I noticed the left rear cable (between caliper and frame mount) was a little bit kinked and wasn't engaging or disengaging fully. So i modified its forward mounting point to increase the bend radius and I oiled the cable. After that the left rear engaged more and released more. This issue was probably why I scrapped it in the first place (seems they do mostly release when cable kink minimized). Now it seems to keep the car parked and releases mostly. It will not lock the rear wheels up when I tried fully engaging it while moving--it acts as if you're gradually applying the brakes. But once stopped it's hard to start again until released.

I took readings with the pressure gauge in the front right caliper and the rear right caliper to compare and summarize the data below.

When pressing the brake pedal as hard as I can and assistant reading the gauge for me. Pressed 3-5 times for repeatability. Rear brake prop valve wide open.
Front right caliper pressure was 1000 psi with car off, 1500 psi at idle
Right rear caliper before e-brake installed: 1000 psi car off and idling
Right rear caliper after installing e-brake with improved cable routing, and eng/diseng several times: 1300 psi car off or idling.
(FWIW, pressure in RR caliper can get up to 1800 psi with e-brake engaged during test)

After the above testing I was pleased to see some improvement in the rear caliper pressure. So I took it for a test drive and recorded the below video to check the operation under panic braking.

https://youtu.be/llfsgcLAuR0

As you can see in the video, the front locks up first, followed by the rear. So now I at least know the rears are participating. But, while this may be preferred to have front lock up before rear, I'm still not fully happy because I would prefer the rears lock up first with prop valve wide open and then dial it back to the ideal amount. So I am still limited in rear brake proportioning control... But I will go with this for now and am at least happy to see some improvement.


Anyone have any similar experience with these brakes?
Why is the rear caliper pressure the same with and without the car idling?
What can I try next? Higher friction pads in the rear? SS braided flex lines in rear (SS up front, non reinforced in back presently)? (HP+ pads in front, and HPS HB580F.627 in rear) ...Only problem with that is the pad selection is limited with Lincoln Continental calipers...


https://static1.pt-content.com/images/pt/2016/02/20160131_122110_zpsf6t3e2xh-1.jpg (http://s393.photobucket.com/user/mitch_mac1/media/20160131_122110_zpsf6t3e2xh.jpg.html)
https://static1.pt-content.com/images/pt/2016/02/20160131_122120_zpsohqnmsxv-1.jpg (http://s393.photobucket.com/user/mitch_mac1/media/20160131_122120_zpsohqnmsxv.jpg.html)
https://static1.pt-content.com/images/pt/2016/02/20160119_205214_zpsrvgrgclr-1.jpg (http://s393.photobucket.com/user/mitch_mac1/media/20160119_205214_zpsrvgrgclr.jpg.html)
https://static1.pt-content.com/images/pt/2016/02/20160119_210413_zpsfvbf6qe4-1.jpg (http://s393.photobucket.com/user/mitch_mac1/media/20160119_210413_zpsfvbf6qe4.jpg.html)

[Apogee]

That's odd that your rear pressures are the same with or without the added gain factor from the booster. Your pretty well at or above the normal operating pressure range, however it's possible that you have a combination of factors contributing, one being the prop valve, and the other being the higher level of system compliance (expansion under pressure) in the rear circuit. The adjustable prop valve moves the set point up or down the pressure/pressure curve with zero being the logical minimum...I'm not sure what the maximum is, or if there is one. On cars I've had gauges on, it was 1:1 up to 1200 psi. Rubber hoses don't necessarily expand linearly with pressure, so at elevated pressures, I would expect to see a greater level of compliance than at lower pressure levels.

Tobin
KORE3

[gator68428]

Thanks Tobin. I am thinking to double check the booster to make sure something didn't happen to it between front and rear testing (did front first). B/c until everything makes sense, I still have work to do.

What do you think about higher friction pads? They do make DTC 60 pads for these calipers. I know those need higher temps to operate well, but I don't think that will be a prob on the track, esp with the e-brake probably keeping a slight clamp on the pads...

Yes that makes sense on the hoses. Sounds like reinforced hoses would be a good place to start. Thanks again.

[gator68428]

(still trying to figure out how to delete this post)
Thanks Tobin. I am thinking to double check the booster to make sure something didn't happen to it between front and rear testing (did front first). B/c until everything makes sense, I still have work to do.

What do you think about higher friction pads? They do make DTC 60 pads for these calipers. I know those need higher temps to operate well, but I don't think that will be a prob on the track, esp with the e-brake probably keeping a slight clamp on the pads...

Yes that makes sense on the hoses. Sounds like reinforced hoses would be a good place to start. Thanks again.

[Apogee]

I don't know that I'd jump up to a DTC-60 pad in the rear...that's a serious track pad that is going to be most at home with something similarly aggressive up front (DTC-70). Both the DTC-60 and 70 compounds don't really become quasi-linear until about 400-500 degrees, so pairing it with something like the Hawk HP Plus up front, which works well at ambient temps, probably isn't your best choice. For Hawk compounds, the DTC-15 or Black compounds would probably be a better choice if they're available.

Tobin
KORE3

[gator68428]

Thanks Tobin. Seems they don't offer DTC15 or black. What about Blue 9012? I see that avlbl, and its a med torque and what looks like a pretty forgiving temp range.

[Apogee]

The Hawk Blue compound is a bit more aggressive than the Black at temperature, but requires more heat before it becomes effective. As such, it is generally used in front applications since that's where you generate heat more quickly, so that would be my only concern running it in the rear with the Hawk HP Plus compound up front.

[trevor572]

Thanks Tobin. Seems they don't offer DTC15 or black. What about Blue 9012? I see that avlbl, and its a med torque and what looks like a pretty forgiving temp range.
Hi. I have had the CPP brakes similar to what you are using, I don't do any autocrossing and have never needed to do an emergency stop, but ever since I have had the car I had noticed brake dust on the front wheels, never anything on the rears. I was about to fit a 1 inch Wilwood master cylinder and a 7 inch single diaphragm booster due to space limitations created by a tall deck engine, do you guy's see that set up working ok for me? Cheers Trevor.

[gator68428]

Hi. I have had the CPP brakes similar to what you are using, I don't do any autocrossing and have never needed to do an emergency stop, but ever since I have had the car I had noticed brake dust on the front wheels, never anything on the rears. I was about to fit a 1 inch Wilwood master cylinder and a 7 inch single diaphragm booster due to space limitations created by a tall deck engine, do you guy's see that set up working ok for me? Cheers Trevor.

My daily driver car always has much more brake dust on the front than the rear. So I'm not sure if the brake dust test is enough.

Measure your manifold vacuum and I'm sure Tobin will be able to let you know about your master and booster choices.

[Apogee]

Hi. I have had the CPP brakes similar to what you are using, I don't do any autocrossing and have never needed to do an emergency stop, but ever since I have had the car I had noticed brake dust on the front wheels, never anything on the rears. I was about to fit a 1 inch Wilwood master cylinder and a 7 inch single diaphragm booster due to space limitations created by a tall deck engine, do you guy's see that set up working ok for me? Cheers Trevor.

Dual-7" diaphragm boosters are not worthless, but pretty close...I can only imagine how little a single-7" booster would contribute regardless of vacuum level. We tend to avoid the dual-7" units like the plague if we can, so are you sure you can't fit a dual-8" or dual-9" unit in your application? Tall deck engine? If you're making less than 12" Hg vacuum at warm idle, you are going to be fighting an uphill battle IMHO.

Tobin
KORE3

[trevor572]

Dual-7" diaphragm boosters are not worthless, but pretty close...I can only imagine how little a single-7" booster would contribute regardless of vacuum level. We tend to avoid the dual-7" units like the plague if we can, so are you sure you can't fit a dual-8" or dual-9" unit in your application? Tall deck engine? If you're making less than 12" Hg vacuum at warm idle, you are going to be fighting an uphill battle IMHO.

Tobin
KORE3
Hi Tobin. I really appreciate your advice, I just tried to get a quick measurement albeit a rough one. I think I could just get an 8 inch dual booster in given the booster is angled up away from the valve cover, worst case scenario I would have to drop back to a dual 7 inch. Would the same size master cylinder bore work on either booster size? And what size master cylinder would you recommend? Thank You, Trevor.

[paul3078]

I have the CPP big brake system in my 71 nova and replaced the prop valve with a wilwood adjustable one and the difference is huge. Before, the nose would dive and you could tell the front was doing most if not all of the work. Now i have it adjusted so the entire car feels like it stops in unison. I have autocrossed a couple times and had issues with the front locking up. Since changing the valve I have been able to balance the front to rear braking. On a side note I still have more brake dust on the front wheels than the rear. Common sense if you look at the difference in brake pad size and the fact the front brakes will always do more work than the rears. I did not have the emergency brake set up and was still able to achieve this braking. I do have an electric parking brake system now connected to he calipers which works well.

[gator68428]

An update.

I just tracked the car at Roebling Road this past weekend on scrub Hoosier A6s (275/35-18s) all around.

I will say that it seems that having the e-brake hooked up and used periodically, along with adding the SS reinforced flex lines from Kore3 (to match the fronts) def helped. I also noticed brake dust accumulate some on the rear wheels! that was a first. I slammed the brakes pretty hard at times coming off of the 130+ mph straight (slowed to 60 or so into turn 1), and the fronts never seemed to want to lock up easily (implying sufficient participation from the rears) and the car stopped as fast as I wanted it to. Here is some video. Tobin, the C6 Z06 front brakes did amazing! Gave me the confidence to pound that front straight as you will see in the fly by in the video.
https://youtu.be/DPp1l9-FuNE

So i take back some of the negativity i had towards the CPP rear brakes. They seem to be working sufficiently well for now. Just need to follow the directions to a T! And get a custom tool to screw the pistons back in when changing pads; really threw me for a loop the first time! But the nice trade off there is that i saved $ on not needing inner drum e-brake.

However, after this weekend I did notice bearing grease oozing out around the seal on one of the front CPP wheel hubs. Tobin worked with me to enable me to reuse my existing CPP hubs (upgraded from CPP front kit as mentioned). This is the seal that was not press fit in for some reason and the grease was coming out around the outside of the seal. The seal on the other hub was press fit and is fine. Seems the process control was not very good on the CPP hubs, different IDs on each... And on the other side i lost a dust cap. I don't think the mating shape was made properly. That's after staking it and distorting the cap some before tapping it in place with some decent force. Still came out. Looks like soon i need to upgrade to the Kore3 hubs. Tobin, are yours screw in dust caps?