Add me to the list of guys that can’t lock up the brakes.
I have tried numerous combinations too.
I started off with 12” front disc with 2.6” calipers and 10” drums, power booster and iron 15/16” master cylinder. Braking was good but I don’t recall ever locking them up. 2006, I added the Dr Diff 11.7” rear disc kit. Braking did not get better or worse.
In 2012, I went down a rabbit hole of multiple changes. My goal was to change to a manual setup for simplicity and a cleaner appearance.
I tried several MCs with different bore sizes and they all resulted in hard pedal, extremely high effort and brakes that wouldn’t even skid on dirt. I changed to larger 2.75” front calipers and that made no difference.
I tucked my tail between my legs, admitting defeat… and put the power booster back in.
Later I realized that I had a disc/drum proportioning valve in place which is wrong for a 4 wheel disc arrangement. I put in a 4 wheel drum distribution block and maybe it was a “placebo effect” but the brakes felt a little better. I pulled the brake pedal and drilled a hole up 3/8” higher to give the push rod more leverage. The brakes felt a little better. Lastly, I adjusted the little nub in the booster that makes contact with the master cylinder piston. All these things made tiny incremental improvements but still…. No lockup.
Last year I upgraded to the 13” Cobra brakes with 2 piston calipers. After reading the brake section of Andy Finkbeiners book, I learned that engineers aim for a 2 to 1 bias for brakes. The front caliper surface area should be approximately double that of the rear in a 4 wheel disc car. With the Cordoba 11.75 rotor, 2.75” piston front brake and 11.7 (1.5” single piston) rear setup, I was at 3.37 to 1. Way too much front bias. With this current setup, I am at 2.1 to 1.
I covered the troubles that I had with the hydroboost installation in another thread.
I tried manual brakes again late last year and had similar results… hard pedal, poor braking.
Even now with the car reasonably sorted out, I can barely lock the fronts. Braking is great but I’m still chasing that “Wow” feeling.