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 650R (ER6). 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. The master cylinder does not have a mirror perch, however, a Suzuki mirror perch is readily available which fits the master cylinder well and works great. It's Suzuki P/N 59671-32F00 and sells for about $12 USD.
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 Suzuki, P/N 59671-32F00.
- You will need an adapter if using the stock Yamaha mirror as your original master had a left-hand thread and the Nissin master uses a right-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.
Using this Master Cylinder on a Stock Seca II:
2009+ Ninja 650R/ER6 master cylinder made by Nissin. Note the adjustable lever:
At full turn (against steering stop). No interference issues with the fairing or windscreen:
Suzuki mirror perch fits well and looks the part:
Using this Master Cylinder on a naked-converted Seca II:
