Recharging Shocks with Nitrogen

[TimSr]

This seems to be the topic of the day, so Ill address it.

I have never in my life seen a shock that "just needs to be recharged". The only way this can happen is if somebody decided to let it all out one day through the fill valve.

Most often, if the Nitrogen is gone it is because it has leaked out, and that means the seals leak. Every guy selling a blown shock on ebay says "it just needs recharged" when in actuality it almost always needs rebuilt. I would never buy one of these unless I needed a good core for a rebuild, because that is almost always what it takes, and you need one with no pitting on the chrome shaft.

What is so special about nitrogen gas? Atmosphere that you breath is 85% nitrogen. Atmosphere (air) also contains oxygen and hydrogen which = water which is an oil contaminent. (This is why you periodically need to change fork oil.) The proper way to fill (charge) a shock requires first evacuating all the air from it before pressurizing it, which means putting it under vacuum. Sadly, even a lot of professional shock rebuilders skip this step, and it reduces the life of the oil in a shock. Then its filled, often as high as 300 psi. Its doesnt take much to allow it to leak right back out again.

Many OEM shocks are not rebuildable. Many are. Every aftermarket shock I know of is designed to be rebuildable. Its usually comes down to whether a suitable good used replacement is less expensive than having one rebuilt. Id recommend looking into this before paying shipping for a blown shock that "just needs to be recharged".

Some guys have some success in rebuilding them at home, but even most motorcycle shops that deal in rebuilt shocks send them to a place that specializes in shock rebuilding, and do not do them in-house.

[Power_Ram100]

Good info!

[Old 179]

I have done 4 shocks over the years. Twice back in the 80's when I used to race. After a season, I would give it to the dealer who I was riding for. They would change fluid and recharge it. With the fluid getting hot ,cool down, ect. it does break down slowly.I felt it worked better after it was done. (one less item to break will racing). Other time it was done on a 200x @ 250r that sat awhile. seem to work better after it was done. ATV Sport mag. November 2001 pg 70 -75 address this. Oil viscosity breaks down in shocks with heating and cooling the same way it effects engine oil. Over time the rebound and compressionrates go out of wack. Over time little jumps will start feeling like bigger jumps. Broken down oil doesn't have the resistance that fresh oil has, so essentially it is like changing your valve stack, but in a bad way. Plus , with less resistance , the shock will bottom out too much and could damage the valve stacks. By changing the oil and recharging the shock, the chance of damage is reduced.

[bigpimpin]

good post!!!

[SWIGIN]

This seems to be the topic of the day, so Ill address it.

I have never in my life seen a shock that "just needs to be recharged". The only way this can happen is if somebody decided to let it all out one day through the fill valve.

Most often, if the Nitrogen is gone it is because it has leaked out, and that means the seals leak. Every guy selling a blown shock on ebay says "it just needs recharged" when in actuality it almost always needs rebuilt. I would never buy one of these unless I needed a good core for a rebuild, because that is almost always what it takes, and you need one with no pitting on the chrome shaft.

What is so special about nitrogen gas? Atmosphere that you breath is 85% nitrogen. Atmosphere (air) also contains oxygen and hydrogen which = water which is an oil contaminent. (This is why you periodically need to change fork oil.) The proper way to fill (charge) a shock requires first evacuating all the air from it before pressurizing it, which means putting it under vacuum. Sadly, even a lot of professional shock rebuilders skip this step, and it reduces the life of the oil in a shock. Then its filled, often as high as 300 psi. Its doesnt take much to allow it to leak right back out again.

Many OEM shocks are not rebuildable. Many are. Every aftermarket shock I know of is designed to be rebuildable. Its usually comes down to whether a suitable good used replacement is less expensive than having one rebuilt. Id recommend looking into this before paying shipping for a blown shock that "just needs to be recharged".

Some guys have some success in rebuilding them at home, but even most motorcycle shops that deal in rebuilt shocks send them to a place that specializes in shock rebuilding, and do not do them in-house.

the only thing id like to add is that the nitrogen is in a bladder in the shock bottle and not in direct contact with the oil.

so the only way it can leak is if the bladder has a hole or someone just lets it out.