MCPV-1 master with disc/disc setup (metering valve question)

[miller54z]

I'm running the MCPV-1 (1 1/8" bore) with an 11" CPP booster on a 1972 Camaro. I have Wilwood 6 piston calipers up front a 4 pistons in the rear. The issue I have is that it seems like when applying pedal, it takes a significant amount of piston movement for the brakes to actually start engaging the rotors. Everything fits together perfectly- there is no 'slop' or 'play' and everything is bled properly (really good pedal with fluid movement as soon as pedal is applied).

Going from a stock disc/drum setup to a 'big brake' all-disc setup with all-new components including the CPP master and booster combo, I was hoping for a more "modern" pedal feel where the brakes engage pretty much as soon as the pedal is applied. Unfortunately, the new brakes feel pretty much the same as the 40 year old brakes did, and it takes several inches of pedal travel before any brake engagement is felt at the wheels.

I know the MCPV-1 has a metering valve installed that is intended for a disc/drum setup to send pressure to the rear brakes to build pressure to a certain level before pressure is allowed to go to the front brakes. I have also read that CPP used to require removal of this metering valve for disc/disc brake setups, but now they say that you can leave it in place for any setup. I'm not aware of any changes that took place to the design of the actual master cylinder itself, so I'm not sure why there was a change to the installation instructions.

I would like to know if removing this metering valve may allow for quicker engagement of the brakes by allowing pressure to pass to all four corners at the same time as soon as the pedal is applied. Would it be advisable to experiment with removing this valve and testing the brakes, or will this cause other problems or require re-bleeding of the brakes?


Thanks,

Matt

[CPPAaron]

2 things to check; Make sure your pedal position is in the lower hole on the booster pushrod. The lower hole in the pedal is for power brakes. If it is the only other thing (based on a proper fully blead system) is you might want to go down to a 1" bore to increase your pedal pressure. Multi-piston calipers tend to like more pressure with less volume.

[miller54z]

2 things to check; Make sure your pedal position is in the lower hole on the booster pushrod. The lower hole in the pedal is for power brakes. If it is the only other thing (based on a proper fully blead system) is you might want to go down to a 1" bore to increase your pedal pressure. Multi-piston calipers tend to like more pressure with less volume.

We are in the correct hole, and the pressure is good: the brakes work just fine. What I'd like to fix is the 3-4 inches of pedal travel before the pressure starts to build and the brakes actually begin to actuate. In most disc brake cars, the brakes engage almost immediately after about 1" of pedal travel. With the MCPV-1, the brakes slowly start to grab after the pedal is depressed about 3 inches. This is why I asked about possibly removing the metering valve, which from what I understand operates by not allowing pressure to the front brakes until pressure builds to a certain level in the rear.

Again, what I am asking is this: Could removing the metering valve possibly allow the brakes to engage sooner? If I remove the metering valve, will this cause any problems within the master cylinder or require re-bleeding of the brakes?

Thank you for your response, but any insight you could offer into the function and possible removal of this metering valve would be greatly appreciated.

-Matt

[CPPAaron]

no need to remove the metering valve... This will do nothing for your your pedal travel. So again the issue would be too large of a bore master. 1" bore will limit the travel. The 1-1/8 with the big multi- piston calipers is causing your Excessive pedal travel.

[miller54z]

no need to remove the metering valve... This will do nothing for your your pedal travel. So again the issue would be too large of a bore master. 1" bore will limit the travel. The 1-1/8 with the big multi- piston calipers is causing your Excessive pedal travel.

Aaron; please explain. We tried the MCPV-1 1" bore master cylinder from CPP first. The pedal travel was LONGER (smaller bore = longer stroke to produce the same volume, but will have more mechanical advantage thus producing more pressure in the system with less pedal effort). A larger bore (1 1/8") produces the same amount of volume with a shorter stroke but will have less mechanical advantage requiring greater pedal effort. Please correct me if I am mistaken, but this is how I understand the physics behind it, and also how it was explained to me by several techs on the phone at CPP.

With the 1" bore, we had an excessively long pedal travel, and Mario along with several other techs at CPP recommended switching to the 1 1/8" bore to SHORTEN the travel- so we did. With the larger bore (1 1/8") master, the pedal travel is shorter. Regardless, the overall pedal travel is not the issue, as it is acceptable with the 1 1/8" bore master cylinder. The problem I would like to address is the amount of pedal travel required before the calipers actually start to engage on the rotors.

This brings me to the question I would actually like to discuss: the function and operation of this metering valve. Every other disc/disc system on the market does not require a metering valve. Metering valves are required with disc/drum systems in order to build pressure to the rear drums before allowing pressure to go to the front discs so both are engaged at basically the same time. Since I have a 4-wheel disc system, I believe this may be delaying the engagement of my front brakes, which is felt as 3-4" of travel before the calipers engage the rotors, which coincidentally is about the same as when the car had the disc/drum setup.

Every vehicle I have driven with a disc/disc setup only requires about 1-2" of pedal travel until the calipers begin to engage the rotors, and I suspect this metering valve may be the culprit. When CPP first introduced the MCPV-1 master cylinder, the instructions said to remove this metering valve for disc/disc brake setups. CPP has removed this from the instructions, and I cannot get an explanation as to why.

I wanted to know if this question could be posed the the engineer at CPP who designed the MCPV-1 (I forget his name, but I have spoken with him in the past through Mario about the master cylinder).

I want to say that everyone at CPP, especially Mario, has been extremely helpful thus far and have provided amazing customer service. I simply want to improve the operation of this brake system, and I would very much appreciate if someone could research the function of this metering valve. I would like to know if its removal would have positive or negative effects within the system- thank you.

Except from ORIGINAL MCPV-1 installation instructions calling for the removal of the metering valve for disc/disc systems:

2404

http://www.bracketracer.com/nova/cppfdb/mc/mcpv1-02.jpg

Very Respectfully,

Matt Miller
CIFCO- Central Iowa Fabrication Company
miller54z@yahoo.com
386-846-0419

[CPPAaron]

Just as I explained in my last post... you are more then welcome to also check with your brake mfg Wilwood. they most likely will also recommend the smaller bore master. Multi-piston setups take more pressure/less volume. The metering valve instructions for removing it can still be followed if you choose to do so but we have found that there is no reason to do so. Just make sure that you get the cover sealed back up so you have no leaks after you remove it.

[miller54z]

Just as I explained in my last post... you are more then welcome to also check with your brake mfg Wilwood. they most likely will also recommend the smaller bore master. Multi-piston setups take more pressure/less volume. The metering valve instructions for removing it can still be followed if you choose to do so but we have found that there is no reason to do so. Just make sure that you get the cover sealed back up so you have no leaks after you remove it.


OK- again, I'm not asking about bore size. To reiterate, we already tried the 1" bore master. While the pressure supplied was slightly more, the amount of 'slop' from initial pedal application to caliper actuation was worse. The overall pedal travel was longer. Both CPP and Wilwood recommended the 1 1/8" bore for my application, and I am satisfied with the pressure it supplies. I am satisfied with the overall pedal travel of the 1 1/8" bore master, but I am trying to eliminate this 'slop' that is present from when you begin to push the pedal until the calipers actually function.

Since you are unwilling to discuss the operation of the metering valve, I only have one last question: I'm taking your last post to mean that the metering valve can be removed from the master cylinder without any adverse mechanical implications. When I remove the metering valve, will this require the system to be re-bled? Also, when I re-install the cover, how does it need to be sealed? Do I need to use RTV silicone or Teflon?

Thanks,

Matt

[CPPAaron]

As long as the pedal is not moved while removing the valve you should not have to bleed again. Since the cap is a normal thead (not inverted flare) you can use a small amount of teflon(just enough to not go beyond the threads)

[miller54z]

If anyone else has any experience with metering valves, please let me know if removing a metering valve from a 4-wheel disc system may help give me a "higher" pedal, or in other words, less pedal travel before brake actuation takes place and the calipers start to engage the rotors. Any advise would be greatly appreciated.

Thanks,

Matt

[kevmurray]

If anyone else has any experience with metering valves, please let me know if removing a metering valve from a 4-wheel disc system may help give me a "higher" pedal, or in other words, less pedal travel before brake actuation takes place and the calipers start to engage the rotors. Any advise would be greatly appreciated.

Thanks,

Matt

Hey Matt,
Did you ever solve this? It sounds to me like you are experiencing the classic fixed-caliper "pad knock back" problem. It causes the pads to have to travel back to the disc and feels like your description. Wilwoods are known for this, especially with a stock rear end. C-clip eliminators help by reducing axle run out but for most people only a floating caliper or a full-floater rear end solves it.

Kevin Murray