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My car runs fine but the brakes seem lacking. I have a system out of a 1995 and I can't even lock them up and the pedal pressure seems very high. Any suggestions on a different year master or an alternative unit to solve this issue? Not sure if I should go smaller or larger,the pedal has very little movement as it sits now and is solid as a rock.Thanks Rich

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When selecting a master cylinders, you should look for M/C that gets you in the bore AREA range 7 thru 10 to 1 ratio when comparing front or rear caliper diameters to the M/C bore. Note a smaller diameter master cylinder applies more pressure on the brake pads, but will increased the pedal travel. Always put a light return spring on both the clutch and brake pedal levers. This will make sure that the fluid return ports are un-covered when you lift your foot. Assuming a manual system you need a pedal lever ratio in the range of 5 to 7 to one. I would start with changing the lever ratio " no cost" just drill another hole further up the pedal lever. Note you should try to keep the push rod with a 7 degree angle so you do not side load the M/C piston. davew

Mark Williams Enterprises recommends a master cylinder that will provide at least 1200 psi. I read somewhere that 1000 psi should lock your brakes. Have you done a pressure check?

You need a smaller master cylinder to reduce pedal pressure, or if the brake system is a single donor setup you may need to change your mechanical ratio on the pedal.

In other words there are two ways to reduce pedal effort, hydraulically or mechanically, you need to determine which is causing your symptom.

If you have a frankenstein'd brake system you may have a hydraulic issue.

Start with the brake pedal mechanical ratio

A ~6:1 pedal mechanical ratio is recommended, if the pedal ratio is good you can assume a hydraulic solution.

This is assuming the brakes are installed and working correctly and there are not other issues keeping the brakes from working.

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Honey anyone?

Yes, smaller, BUT, be aware that it's the area of the piston that matters, so you have to square the size difference.

For example, if you go from a 1" master cylinder to a 3/4", that "appears" to be a 25% reduction in foot pressure, but it's not. The actual ratio is:

New foot pressure = Old foot pressure * (new master cylinder diameter )^2 / (old master cylinder diameter )^2

So for the above example:
New foot pressure = Old foot pressure * (0.75)^2 / (1 )^2
New foot pressure = Old foot pressure * 0.56

So, stepping down from 1" to 3/4" means that you'll pretty much cut your foot pressure in half.

The potential gotcha though, is that you now get twice the foot travel, which may or may not be a big deal. If there is air in the system, it could use all the pedal travel compressing that instead of slowing down the car, so it's always a compromise.

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Just adding: It is simpler and quicker to use (.75/1)^2 You get the same answer.

I can't say that I ever tried to lock up the wheels on dry pavement on my build. It did stop very well. Enough for me. It had 4-pot front calipers and single-pot rears.

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Chuck.

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