Help ID front master cylinder please

Working on a restoration/revival project. Master cylinder is shot, don't know if it's the stock single caliper master cylinder (1/2") or the larger dual disc version (5/8"). I only have a single brake disc, but from what I've read, the 5/8" master cylinder can be used for either set-up.

Any good way to ID them? Just disassemble and measure? Outside looks like this...



Doesn't work at all, apparently sprung a leak in storage some time in the last 8 years.

Look underneath it to see if the size is cast into it. Ed

Could be stamped (or raised-letter)

14mm OR 5/8"

The smaller bore designed for single caliper may produce over-sensitive braking when fitted to dual calipers.

The larger bore designed for dual calipers may produce under-sensitive braking when fitted to a single caliper.

Good Fortune!

When restoring the master cylinder, be sure that the tiny relief port is clear and open which allows fluid transfer between the reservoir and bore.

The other larger port supplies fluid to the bore.

Good Fortune!

LukeMacPU wrote: Working on a restoration/revival project. Master cylinder is shot, don't know if it's the stock single caliper master cylinder (1/2") or the larger dual disc version (5/8"). I only have a single brake disc, but from what I've read, the 5/8" master cylinder can be used for either set-up.

Any good way to ID them? Just disassemble and measure? Outside looks like this...

Doesn't work at all, apparently sprung a leak in storage some time in the last 8 years.

That looks old and no good. It looks original on your Z1. It is a single disc.
If you find a rare 5/8 bore, there is a stamped 5/8 near the bottom side of the triangle piece were the lever bolt goes through
Either buy a new aftermarket one, or an ebay one, or machine yours bigger to the 5/8" bore.
When you take yours apart it will be all oxidized with moisture, the bore will be no good, all pitted for a stock rebuild kit.
It looks you are in no hurry are you?
I am in the process of putting a couple of both 1/2" and 5/8" together. I have plans of ebay in the near future. 1/2 rebuild part kits are $38 and 5/8" kits are in the upper $50's.
Then you have glass beading and labor involved.
There is a Guy in England that sells 5/8's for $250 Or the chinese nock offs for $139.
Plenty of options out there.
Keep me in mind.

Thank you all for the help/information. Got a rebuild kit and I'm back in working condition.