As these bikes age, one common failure seems to be the master cylinder reservoir sight glass. I've owned three Seca II's I've had to replace the master cylinder on all three because of seepage at the sight glass.
The stock master cylinder on the Seca II has a 14mm bore. When sourcing a replacement, a master with the same size bore is recommended. In this instance, a larger bore is NOT better.
I've had great luck with the Nissin master cylinder from a 2009+ Kawasaki Ninja ER6N. This master cylinder has a 14mm bore and an adjustable lever making it a great replacement for the stock unit, especially on a stock Seca II with the single front master.
There are a couple of considerations when replacing your stock unit with this Nissan unit.
- The Er6N version of this master cylinder has a built-in mirror perch. The Ninja 650R version does not. If using the Ninja 650R version, use the mirror perch from your stock Seca II master cylinder.
- If using the version with the built-in perch, You will need an adapter if using the stock Yamaha mirror as your original master had a left-hand thread.
- The Nissin master uses a pair of spade terminals for the brake light switch. The connector for the brake light switch will have to be cut off and a pair of spade terminals installed.
