Calculating master cylinder size

[Rob]

Hey guys - happy new year!

So, I'm trying to compare two master cylinders to see if the standard Marina one will serve the new Capri calipers and drums.

The Marins MC is:
19mm bore
37mm stroke

The Capri one is:
19-20mm bore (close enough?)
35mm stroke

Now, I've taken the bore size without taking the piston out, just measuring the top part of the piston up to the edge of the cylinder - is that accurate enough?

Also, how close do they need to be, ie is my 19-20mm measurement good enough or should I remove the piston to get a good measurement.

Any help appreciated
Rob

* I've posted this on Rods'n'Sods too so I'll cross-post any useful responses

[CIH]

I have a similar issue running S14 4-pot calipers on an S12 which came with single sliders. Generally, it's a case of suck it and see. I have a terribile peddle, but I think I have other issues too.

[Rob]

Well that hasn't filled me with confidence! ;D

I know what you mean though CIH, I think every custom setup will react differently. If I can't get the Marina one pumping well enough it's a new pedal setup so I'd rather get it as close as I can while it's in pieces!

[bortaf]

what colour is the plast ziptie around the capri master (thats what tells you the bore size exactly) it should be red which is 22.2, possably orange 20.6 ? you need to workout the overall area of the cylinder so near enough isn't really good enough TBH.
I have an XLS sheet I use to work out the differances in cylinder fliud movement if you want i'll upload it and share the link, you'll just need to put in the differant sizes and it'll tell you how much it's changed so you can match master to caliper AND rear cylinders, don't forget the rear cylinders !

Here just uploaded it to a file sharing site

rapidshare.com/files/685520927/mastercyl.xls

[scruff]

Correct me if I'm wrong but: Brake fluid doesn't actually move much though so the stroke *should* be irrelevant. (Fluid is incompressible and the pads shouldn't move )

It's only to pressurise the system so it's the cross section that is important.

Bigger cross section = more pedal effort for the same given brakes.