You mentioned it was firm when you capped the master cylinder off.

The only other thing I can think of would be any Flexible lines. If you have rubber lines, maybe 1 or more is getting soft.

Have someone else pump them up while you inspect them for bulging.

 

it has Russel braided flex lines that I put on probably 4 or 5 years ago. I’ll go around and check that something didn’t damage them while the wife pumps the brakes.

 

What master cylinder and front calipers? If you replaced the master with a smaller bore, did you change the pedal ratio? I feel you may have a fluid volume mismatch.

 

Stock 4-disc master cylinder and front calipers but I moved the pin location up to where it’s a 6:1 ratio

 

Well that's a red flag. You are not moving the piston enough. I don't see why that would work. A manual brake master cylinder should have a smaller piston using a longer stroke.

This is all just opinion

 

The kit I purchased has different options for what M/C you use (Stock, Strange, Wilwood IIRC) but I agree that I need a different M/C. I feel like I have a volume mismatch with the stock M/C as mentioned by BigKID.

I’m gonna look for some kind of calculation similar to finding brake PSI. When I did my braking psi calculation, everything checked out but volume may be another story and the math doesn’t lie.

 

I found a brake calculator of sorts today and started fiddling with it. It’s an excel work sheet from Busted Knuckles Off Roads website. Going by their guidelines I should be aiming for an overall leverage of around 190 for manual brakes.

With all my stuff plugged in I’m at 119 with a stock bore size (1.338”) and a 6.4:1 pedal ratio. Not good.

Now if I drop the bore size down to 1 inch, I get about a 212 overall leverage. Much better and that’s a 78% gain.

Guess I’ll be looking for a smaller master cylinder.

 

Leverage of 190, 119, and 212. What do those numbers mean? Ratio? Lbs? %?

 

it doesn’t really give a unit of measurement for it

 

Here is the brake calculator that I used when I upsized my MC and rear calipers: https://www.tceperformanceproducts.com/bias-calculator/

I agree that it sounds like your Master Cylinder size may be too large diameter.