Even even more critical than the bore job would be the circlip groove for assembly retention.
Of course. That's why this is not a job for the machine tool challenged. At any rate, if you have the necessary machines and tooling to do this you could easily make a master cylinder body from billet that would work with a suitable piston assembly. It all depends on your resources and knowledge.
This a real good point.
Just one thing though, the above is a legit and easy method to use, as long as one is not trying to compensate for excessive lever travel for any given amount of braking force applied at the wheel.
The thing to keep in mind that by virtue of the master piston moving, displacement is occurring, so as master piston diameter decreases, the stroke has to increase in order to maintain the same volumetric displacement.
The theoretical hydraulic non compressible fluid regime only begins after the pad clearance is gone and the pads are starting to load up on the rotors.
Good point. In general I go for a master cylinder piston a bit larger than is fitted stock and make adjustments to the mechanical end of things to get the feel right. This is the sine qua non
of radial master cylinders -- too big a piston pushed by a greater mechanical ratio, resulting in a rough approximation of the original ratio, or whatever change you are looking for. In point of fact the mechanical end of things is the only real adjustment possible for the average end user.
By the way, here's the formula I use to determine the overall ratio. Notice I'm not doing the PI * Radius squared for the diameters ... all that is needed is to square the diameters to get an accurate result.
Ratio = (1/MCD^2)*((LP^2 + MiP^2 + SP^2)*NP)*(PTF / PTP)
MCD = Diameter of the master cylinder piston.
LP = Diameter of the largest piston.
MiP = Diameter of the smaller piston. If you're not working out a four piston caliper equate to zero.
SP = Diameter of the smallest piston. If you're not working out a six piston caliper equate to zero.
NP = The number of only one diameter piston. Ex.: for a two caliper setup NP = 4 (four largest pistons)
PTF = Distance from the lever pivot to the point where your fingers rest on it. If using multiple fingers arbitrarily equate to the mean center of all fingers.
PTP = Distance from the lever pivot to the piston. Usually specified by the manufacturer.
Be sure to keep all measurements in the same units. I always use millimeters, but it will work in inches ... or miles if you prefer.
If you are working out a single acting caliper remember there are actually two faces the pressure bears against: the piston and the back of the bore it is housed in. This side pushes the mobile part of the caliper in the opposite direction as the piston(s), applying force to the inside pad(s). NP will be the same as if you were working out a double acting caliper.
FYI, I usually shoot for an overall ratio in the neighborhood of 100:1. This can be adjusted up or down to suit your preferences and to compensate for softer (sticky) or harder (slippery) pads.