Cincinnati Rick

What's involved in doing a power brake conversion on 1970 442 with manual disks?

Rick

joe_padavano

The easy way is to simply unbolt the M/C from the firewall, pull it forward, remove the pushrod, boot, and retainer, and install the booster in between. There was even a dealer-installed kit for this. What that doesn't get you is the correct M/C bore, as a manual brake M/C usually has a smaller bore than a power brake M/C to provide more hydraulic "leverage". This will work fine but will require slightly more pedal travel than if you swapped to a power brake M/C. You can do that if you want, as well as replacing the hard lines from the M/C to the distribution block/combo valve for optical reasons.

Cincinnati Rick

Joe,
I picked up a booster/master cylinder from OPGI. Part # CH25896
Can I use my existing distribution block or do I need to install a proportioning type block?

Thanks
Rick

joe_padavano

If your car is a factory manual disk brake car, you should have the rectangular distribution block on the frame rail and the separate metering valve under the master cylinder. Those same parts work with either manual or power brakes, so no need to change.

Metering valve:



Distribution block:

Cincinnati Rick

Well I was told it was a factory manual disc/drum set up. However there is no metering valve just the distribution block. It had a dual reservoir M/C when when I bought the car. Would that negate the need for the metering valve?

Rick

joe_padavano

ALL disk brake cars have a dual reservoir M/C. Sounds like this was converted. You can either get a repro of the original metering valve if original appearance is important to you, or get an aftermarket combo valve to replace the distribution block. Either way works, the factory simply went to the combo valve in 1971 to consolidate parts and save manufacturing cost. If you do select the combo valve, I'd suggest the newer aftermarket brass ones, as they don't rust internally like the original cast iron ones.

Cincinnati Rick

Thanks for the info Joe. I'll order the repro combination valve since I'm not worried about stock appearance.

Rick

lemoldsnut

Hey Joe, Can you school us on why there is a metering valve?

Thanks
Larry

Koda

I am not Joe, nor do I have his knowledge, but, from what I read, the calipers take a lot more hydraulic pressure/flow to move, so the metering valve favors the front brakes so that they work in tandem with the back brakes. If you don't have one, I think your back brakes lock up before the front ones work enough. I could be wrong.

lemoldsnut

Interesting. I have a factory disc brake car we drive now and then and that is exactly what it does during hard braking and it has one on it. I am now curious if it is not working correctly.

Thanks Koda

joe_padavano

Nope, you are correct. The metering valve is a proportioning valve. The problem is that drum brakes are self-energizing. In other words, as soon as the leading edge of the shoe touches the drum, friction pulls it in, increasing braking force. Disk brakes don't do this, so it takes a little more pedal force to generate the same stopping torque. Without a metering/proportioning valve, the rears would lock up first, potentially causing the rear end to slide if you were braking in a turn. The metering valve delays the start of rear brake engagement to prevent this premature lockup.