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435 Posts
Based upon all the posts on the Fox air shock "stuck-down" problem it looks like it has not gone away. After studying the Fox patent (6,135,434) it is apparent that the problem occurs when the sliding seal inside the sleeve leaks momentarily while the shock is compressed. The high pressure air from the "air spring" side moves into the negative pressure chamber. This increases the negative pressure causing the shock to stay compressed. When this happens on the trail, the bike is difficult to ride because of pedal to ground interference.
The fact that the shock stays compressed indicates that the seal is no longer leaking (otherwise the pressures would equalize and the nitrogen fill in the damper assembly would force the shock open. I suspect that the momentary leak is caused by twisting of the seal or some other dynamic problem that only occurs during rapid movement of the piston. The "cold weather" theory may also be one of the factors, since low temperatures shrink the seals and make them stiff.
If there was a way to manually vent the negative pressure chamber it would allow the rider to de-compress the shock, pump it up to the correct pressure, and get home.
In looking at my Triad (2006 Stumpy FSR) there doesn't appear to be enough metal thickness in the sleeve to install a vent valve.
Suggestion to Fox........ add a boss on the sleeve with a small manual vent valve. This would also eliminate the potential injuries due to the sleeve flying off during disassembly of a stuck-down unit.
The fact that the shock stays compressed indicates that the seal is no longer leaking (otherwise the pressures would equalize and the nitrogen fill in the damper assembly would force the shock open. I suspect that the momentary leak is caused by twisting of the seal or some other dynamic problem that only occurs during rapid movement of the piston. The "cold weather" theory may also be one of the factors, since low temperatures shrink the seals and make them stiff.
If there was a way to manually vent the negative pressure chamber it would allow the rider to de-compress the shock, pump it up to the correct pressure, and get home.
In looking at my Triad (2006 Stumpy FSR) there doesn't appear to be enough metal thickness in the sleeve to install a vent valve.
Suggestion to Fox........ add a boss on the sleeve with a small manual vent valve. This would also eliminate the potential injuries due to the sleeve flying off during disassembly of a stuck-down unit.