hi can any one help me i have a zxr400h rear shocker that has the expansion bottle and just wanted to now if it should be gas filled or oil filled many thanks for any advise

 

Welcome to KF

The "expansion bottle" should be just that. Using oil, a bladder with Nitrogen as the inert gas. The bladder is the separater, while the Nitrogen is pushed back and forth by the oils exertion against the bladder. Nitrogen will not heat up as bad/fast because it is an inert gas and is more controlled lets say.

If you need to rebuild the assembly, hook up with your favorite suspension tuner. Money well spent.