Coveman
I'm Awesome
1998 Master cylinder piston:
As to more pressure, I would need the piston diameters to tell. Larger master piston will exert more pressure on the calipers and rear brake slave cylinders for the same amount of stroke on a smaller piston.
Basic hydraulics.
Not so fast! A smaller diameter MC creates higher pressure at the caliper.
Two hydraulic cylinders interconnected
Cylinder C1 is one inch in radius, and cylinder C2 is ten inches in radius. If the force exerted on C1 is 10 lbf, the force exerted by C2 is 1000 lbf because C2 is a hundred times larger in area (S = πr²) as C1. The downside to this is that you have to move C1 a hundred inches to move C2 one inch. The most common use for this is the classical hydraulic jack where a pumping cylinder with a small diameter is connected to the lifting cylinder with a large diameter.
The OBS truck had a step, or two sized (something like 40 and 28mm) bore in the MC. This NBS MC swap gives us a single, or straight bore (33mm in my case; 1 5/16 inches).
On the step bore OBS MC, the primary bore pushes high volume up to a certain pressure then transitions to the smaller secondary bore and begins to develop pressure at a more rapid rate.
When CAFE standards for the OE's forced them to design more towards fuel mileage, low drag calipers became the norm. Low drag calipers have chamfered seals that retract the pistons further than necessary to make sure that they don't drag on the rotors which was supposedly good for 1-3% better mileage. Since the pistons have further to travel before making contact with the rotors, the quick take-up MC achieves this with the primary bore. The secondary bore gives us higher pressure but with a longer throw--That's the spongy feeling we had.
I'm still trying to figure out my next step, but ditching the low drag calipers seems to make sense. A larger caliper like from the heavy half-ton should create more pressure to the pads. The 1 5/16 MC that I installed gives me a very firm pedal, but I'm no where near locking up the wheels yet
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