Would it be sensible to overbore master cylinders in the hope of getting a softer clutch and "better" brakes.

I'm talking tin can type, I understand the later type where larger anyway? (if so how much larger?)
As some of you may know I have upgraded to front discs but don't intend to run a booster.

Would this be a worthwhile en-devour?

If you increase the bore of the brake MC you will get a heavier pedal, ditto for the clutch one too.
This is because you are moving more fluid at a given pedal stroke.

For example,
When the 998 Cooper came out, to reduce pedal effort they went down to a 0.625" diameter MC, and got rid of the hydraulic intensifier the 997 Cooper had.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

The good doctor is correct about the effects from increasing the diameter of the master cylinders, and their piston areas, but incorrect about the reason behind it.

Because hydraulic pressure is measured in psi(pounds per sq. inch), the area of the pistons involved, both in the master cylinders on one end, and those in the caliper, wheel cylinder and slave cylinder on the other end, determine just how much effort is required to move fluid or have the fluid move something on the receiving end.

So, a piston of larger area in the master cylinder, with no other changes. will require more effort than a piston with smaller area.

On the receiving end (caliper, wheel cylinder and slave cylinder), a piston of larger area will cause more force to be applied to the pads, shoes or clutch throwout/release bearing for the same amount of foot pressure on the corresponding pedal.

I recognize that this is a rather fine distinction, but it is really the pistons' relative areas which determine pedal pressure required or the force applied at the other end. Of course, the amount of fluid moved is related to the area of a piston FOR A GIVEN STROKE. Of course, this is only the hydraulic side of things and does not take into account the mechanical advantage for the relevant pedal's length.

_________________
"it's always better to be uninformed than ill-informed"

7boy, yes I was fully aware of this and you are correct, I just didn't want to write a long treatise to explain it.
I tried to do it in simple terms......

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

So a small bore long stroke MC with a big bore short stroke slave or caliper will be the best combination, correct

_________________
Respect mine and I'll respect yours.

Yes for brakes, but the pedal will go down further.
As for the clutch MC I had a long pushrod in a 0.7" one, it worked but felt weird having to lift my foot so high.
IMO a 0.75" is best MC for clutches, they still work even with a bit of the usual slop in the linkages.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Doc - I only took the trouble, and novel, to explain it because so many people seem to get it wrong. Many people get it exactly backwards when all they have to do is remember to think in terms of piston area and psi.

_________________
"it's always better to be uninformed than ill-informed"

Twud be more sensible to resleeve to standard with a Stainless Steel sleeve and making sure the rest of the braking system is in tip-top condition

_________________
"Show me the Mini!"

I thought oil pressure was measured in BAR not PSI, well ya learn something every day!

bar/ psi depends where oyu are in the world, a bit like smanner sizes.

I think you would find that 90% of the people on this forum would use psi or kpa for oil pressure.
Show me a 2" Smiths dash oil pressure gauge in bar.

Hi KIrby, Clutch & Snake in Geelong do a stainless m/c re-sleeving service.
Had mine done recently, should last longer than the original m/c lining which is subject to pitting etc as we all know..

_________________
'98 Mpi Sportspack + 7 port alloy head

Any idea on a rough price?

I'll have to dig the receipt out. I'm sure it was cheaper than a new one.
Best thing is to give 'em a call, ask for Mel and say you are a local Mini owner.
They have sponsored our Western tour with a prize before and should be very helpful.

_________________
'98 Mpi Sportspack + 7 port alloy head