The problem here is you don't understand the hydraulics as well as you think you do. You certainly don't understand the "step bore" because you continually describe it's function incorrectly.
I'll accept that I haven't described the function of the step-bore FULLY. I have not described it INCORRECTLY. (See below)
If I have, point out what I'm getting wrong, so I can learn.
The constant bulling from you on this subject is getting boring and I'm tired of it enough to respond. The large bore of the NBS master cylinder is able to fill the caliper chamber quickly and push the piston out just fine. Likely there is an increase in needed pedal pressure because the size change but it appears most folks are OK with that given the number of them that make the switch.
1. I need to repeat myself because folks keep starting new threads giving the same CRAPPY advice.
2. Someone modifies their truck, (hopefully) knowing the change in pedal pressure that occurs. And they're good with that. Then they let their wife or kid drive it, and the spouse/kid has no concept of how much force they're going to need to apply in a panic stop.
These non-step-bore master cylinders are borderline UNSAFE for the unwary driver. The larger bore size is NOT matched to an increase in booster power.
GM has used low drag caliper a lot longer then this abortion of a master cylinder, there is no magic in it.
1980, or thereabouts. First I remember them was on GM FWD "X-Bodies".
34+ years ago when I was in school for this stuff we were taught to understand the theory of what we were fixing so we could logically find the fault when it arose. We were taught almost all theory as opposed the model specific stuff taught now. I'm factory trained by both GM and Ford and with 30+ years as a professional mechanic, and more than that tinkering with hot rods and such. You seem like you have a good general knowledge but for God's sake cut out the loud mouth look at how smart I am stuff and calling people names because they don't capitulate to your opinion. Stuff like this is why most guys keep quiet and never offer advice. There is always someone with marginal knowledge that wants to argue about stuff they don't understand.
OK, here's the theory:
Requirements
1. Pedal effort has to be kept reasonable so that old ladies can drive the vehicle. Vehicles with larger master cylinder bores tend to have more-powerful brake boosters to compensate for the lack of hydraulic advantage.
2. Brake drag has to be minimized to meet CAFE requirements, and to be competitive with "official" EPA fuel-economy estimates.
3. The brakes still need to stop the vehicle without excess pedal travel.
Solutions
Calipers are then designed so that the main, square-cut seal retracts the piston farther than previous designs. Provides a small "air gap" between pad(s) and rotor. These calipers are known as "low-drag" units. Fuel economy improves...a little.
Downside of this is that it takes additional fluid movement from master to calipers to push the pistons out, so that the pads are back in contact with the rotors. It's the opposite to retracting the pistons an extra amount.
Therefore, to effectively and safely use "low-drag" calipers, a special, stepped-bore master is required, having three pressure chambers instead of the previous two chambers--a primary and secondary piston as usual for a dual-circuit master cylinder, plus a third, larger-bore chamber specifically to accommodate the needs of the low-drag calipers.
The larger-bore piston provides fluid at
low pressure/high volume.at the beginning of the brake pedal stroke, that pushes the pistons out without requiring a long pedal stroke. The usual primary and secondary pistons are moving, too, but since the brakes haven't actually applied, (caliper pistons still traveling outward, rear wheel cylinder pistons still moving against return-spring force) they're still under low pressure, too. Therefore, initial pedal pressure is low, and pedal travel is reasonable.
Result: Lots of fluid provided primarily to front calipers, gets the pistons moved out with little pedal stroke and little pedal effort.
Once the pistons are out, so the pads are against the rotor, the high-pressure section of the master cylinder (the smaller, 1" or 1 1/8" bore) provides the higher pressure needed to force the pads into heavy contact with the rotor to apply braking force. Because the hydraulic advantage of the high-pressure part of the master cylinder hasn't been
SCREWED UP by using an oversize main bore, pedal force is still reasonable. Since the only fluid movement is to account for caliper flex, pad compression, hose ballooning, seal distortion, etc., pedal travel is reasonable.
The "two-stage" Quick Takeup master cylinder has advantages that a single, larger-bore master cylinder can't hope to match. It takes the two-stage master to achieve large fluid volume required by low-drag calipers, while NOT requiring high pedal effort or long pedal travel.
^^^^What part of this is incorrect?
So, yeah, some doofus tries to re-engineer the brake system using incorrect "magic" parts,
without having the understanding of what the compromises are, or WHY GM built it the way they did--and then broadcasts this silliness all over the internet.