I know I've asked this before but i don't think anyone ever came up with the answer. What is the bore of the stock Track/Kick master cylinder. Some one must know pleeeease. Also someone (Digger?) mentioned that the LWB booster is bigger, can anyone confirm that?
TIA

you getting issues with the lwb calipers or is this back to the rear brake conversion , i know it doesnt answer your question. just interested as work on your vit seems to be coming on as your missing a lot not being on the road ?

Its really the issues with the rear discs, I will have made things even worse now with the bigger front calipers. I haven't bled the system through yet as I will probably have  to strip the m/c to measure the bore. If I can sort out a different master cylinder I will have another go at a rear disc conversion using Rover calipers and machined brackets. If I can't get it to work properly then I have LWB rear drum brakes that I can use. I still have problems with the brake lines too, the braided lines keep leaking and the stock rubber lines are too short with the extra drop I get with the OME struts. Lots of things to sort yet.

I don't know for sure if the LWB M/C is bigger or not, but I can see why you are having problems. In stock form, the m/c's rear section only has to push a little fluid to make the small drum brake cylinders extend and apply the brakes. When you change the rear over to a disk brake setup, the rear calipers need much more fluid volume to apply the brakes than the old drum brake cylinder setup and the m/c doesn't push any more than it did with the drum brakes(unless you upgraded the m/c when you changed to disk rear brakes).

I don't know for sure if the LWB M/C is bigger or not, but I can see why you are having problems. In stock form, the m/c's rear section only has to push a little fluid to make the small drum brake cylinders extend and apply the brakes. When you change the rear over to a disk brake setup, the rear calipers need much more fluid volume to apply the brakes than the old drum brake cylinder setup and the m/c doesn't push any more than it did with the drum brakes(unless you upgraded the m/c when you changed to disk rear brakes).

Exactly and the LWB pistons are 54.5mm as opposed to the SWB 48.1mm which represents nearly a 30% increase in volume.

Didn't I read somewhere that a Subaru Master Cylinder was the fix for this or am I thinking of something else?

I think that a pontiac fierro will fit also. not sure what year maybe there all the same?

Not all Subaru m/c are the same, some are 7/8 which appears to be the same as the Track/Kick.  The one to get is apparently a 1 1/16" (see my other thread - SWB brake upgrades). Firebird m/c has been used too. Not very easy to get hold of over here but probably more common than a Subaru in the US. Just to complicate the issue my Vit has Lucas/Girling brakes so the m/c may be different to the Jap fit Aisins.

Unless I'm wrong about this, once the
caliper is full of fluid, and the air gap between
the rotor and pad is gone, the volume of the
master cylinder should make little difference.

The problem would come up with drum brakes,
as they retract to their rest position from spring
tension pulling them back, disk brakes use no such
spring.

I will be the first to admit, brakes are not my
strongest field in mechanics, so help me out here

Wild

The piston retracts when the pressure is removed. The seal 'distorts' and prevents it moving back too far but there is still a gap. If you make an analogy with compression ratio. Make the cylinder head twice the volume and you need twice the air to fill it to the same pressure, of course now you have twice the air you get twice the power 

Agreed, what would the seal deflection
come out to if it can be measured? I never
thought about the seals retracting the pistons