I'm running the twin brake master cylinder setup with pedal bias bar. I stripped the brakes some time ago. I'm fecked if I can remember which bore master cylinder feeds the front and which the rear?

One mst cyl is 5/8. The other is 3/4.

Anybody justification for which where?

big difference in size normally 5/8" and 0.7" can be mixed --- the small bore gives more hydraulc pressue but "pumps" less fluid.

What brake are you running front and rear - if you are running Siera disks I would expect the big cyliner to go to the rear.

MKII discs front on std serria M16 calipers twin pots. Rear, again MII discs with std seirra sliding rr calipers

The more I think about this I should have 2 very similar master cyl bores ... the bias bar making the adjustment on the actuator rod accordingly. Opinions on this?

Not really, you want the bores matched to the brake pistons so that the bias bar is as central as possible for typical braking conditions. The larger bore is almost certainly for the front.

Larger bore to the rear as you want less braking force there. The larger bore will shift more fluid, yes, but will generate lower pressure, meaning less braking at the rear.

timbo7 - I have the same brakes as you...M16 up front and Sierra sliding at the rear. My master cylinders (on an ST Motorsport pedal box) are 5/8" to the front circuit and 3/4" to the rear circuit. Even with a difference in bore as large as this the bias is still wound a good deal forward to get the brake balance right. These settings were advised by Ian Gray at STM and verified to work extremely well on the SVA man's rollers.


HTH,

Eddy

I've the same ST pedal box.. I distinctly remember, like you, having to wind out the balance bar to get a frt/rr balance that worked well on the track ..

Cheers

Wow, I'm quite surprised. My apologies for offering the wrong information, I should know better than to post without having experience with the parts. I didn't notice BT's recommendation of large at the rear, if I had I would have deferred to him.

Why is the system so poorly designed that it needs to be wound far forward? Were the calipers on the rear originally used for fronts?

large to the rear, but I am using 5/8" cyls front and rear, with Raceleda M16 4 pots on the front and std sierra rear handbrake calipers..........................kinda hoping it'll be ok with adjustment on the balance bar at that, if not may need a 3/4" for the rear cyl.