Hello all
I own an 09 YZ250 and think I have to change the rear shock oil. The shock action has become somehow softer in the last months or so and I wonder if I can just change the oil without touching the nitrogen? I have no access to nitro so I'd love to just change the oil. I reckon that after 3 years some deterioration has happened. No oil loss I aware off.

I've found a lot of info on rebuiding but I don think I have to go that far. Can't I just unscrew the dampener assembly and change the oil? Another thing is that I only have W10 forkoil available I hope it will work with that oil. Can I use it?

Thanks in advance

arnego2, on 10 April 2012 - 06:06 AM, said:

You need suspension fluid, no you have to let the nitrogen charge out of the shock to disassemble it or you may need stitches. You can change most of the oil out via the resivoir cap but a complete change requires removing the shaft.

Thanks that is not what I hoped for, so I also have to let out all the nitrogen even if I just change the oil in the reservoir?
The W 10 oil is a fork oil so it should be a suspension fluid, or am I wrong?

Shocks use 2.5w and fork oil breaks down too fast in a shock. You should use some real shock oil if you go to the trouble of rebuilding it. If you really can't find nitrogen in your area use air, its better than nothing. You need the pressure to keep the seal head well seated on the rebound stroke.

Hm good to know thanks, so I have to put it off a little and try to get the suspension oil from up north.
A mate told me of a shop dealing in gases (for welding) lets see if they have adoptors to put nitro in there.
Could there be any other reason why shocks turn plusher over time? So a higher (oil) weight could harshen up the rear suspension?
My weight has not changed much, well I lost 2 kg over the last weeks

Absolutely do NOT try to disassemble the shock without letting all the nitrogen out first! The nitrogen pressurizes the entire shock body and fluid, and it will burst in your face.

The purpose of the nitrogen (or air) is to keep the fluid under pressure so it does not cavitate. If you didn't have it the fluid would get all full of micro bubbles (kind of a frothy look) upon rebound and would become useless as a damping medium.

If you let the gas out you will see. The shock will become useless instantly.

Where are you located? Costco in (NJ USA) has nitrogen because they use it to fill all car tires now. They filled my shock for free but could only go up to 120psi (which works fine btw). I later went to a suspension shop to bring it up to 150 as required. You can definitely use regular air as a temporary fix. Just won't be as stable over temperature. Are you sure your shock is pressurized now btw? When you take the spring off, what happens to the rod? Can you push it in?

EDIT: Definitely use 2.5 W shock fluid as others have said.

Edited by rjpjnk, 11 April 2012 - 10:22 AM.

Thanks for the information
I came to the conclusion that I've to rebuild and that due to non availabilty of nitrogen air seems to be the best alternative available.
Here I got what I planned to do > http://www.thumperta...uild-using-air/