Clutch master cylinder size

my clutch m/c says 14. I was looking at masters on flea-bay and some are 14 and some are 1/2. what's up with that. what size is your's? mine is a '98.

 

The stock clutch master on the 5th gen is indeed 14mm.

If you use a smaller diameter master you will get a bit more lever movement but more importantly more mechanical leverage over the pads. In other words for a given squeeze with your hand, you'll get more force applied to the pads.

The leverage effect is based on the area of the MC piston, so 14mm has an area of 154mm2 and the 1/2 inch has 127mm2, so you'd get an 18% increase in pad force (and 18% more lever travel). That might make the brakes more touchy or lock-prone, but I'm willing to bet that just changing to different pads (e.g. EBC HH) from stock would give something of a similar magnitude. YMMV.