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Have a pair of Sid xx dual air forks, been having an issue where they suck down in the travel after about 3 rides and I have to keep letting air out of both chambers and re inflate to get all the travel back. I have tried 5 to 10 psi more and less in the negative than the positive chamber but still sucks down. I prefer with slightly more in negative and makes fork more plush on small bumps etc. At the start of a ride they suck down around 5mm, the 10 percent indicator on the stancion is just inside the wiper seal, after a few rides it pulls down to the 20 percent Mark, this is around 20mm. The forks have had a complete service, with every seal replaced.
Bump
I thought they they sucked down a bit and was normal. Do you still achieve desired sag?
The forks have had a complete service, with every seal replaced.
Could be the positive is loosing pressure, causing an imbalance between + and -, would check pressures next time it happens to confirm/rule out.
A vacuum in the lowers is also a possibility, did you service them and reassemble with forks compressed? If so, with forks at full extension slide a cable tie down past the dust/ oil seal, this will allow air into the lowers and the pressure in them to equalise with atmospheric pressure.
I had exactly this issue after I put new seals. Worked out I had put wrong thinner seal on the negative chamber piston. It's the smaller diameter fatter one you want. I know it's counter intuitive to fit a fat tight seal on, when a perfect fit but narrow seal is also in the kit.
You want the same on bottom plug. These should be a tight push up the inside of stanchion.
Easy to tell if air is migrating between negative and positive and a dust seal blowing off is another giveaway.
Wip them out and try again
Ebay seal guy is ace for rockshox.
You are 20mins away from a fix. Seal kit£9.
I prefer with slightly more in negative
There's part of you problem.
By design, a dual air fork will suck itself down if you run more pressure in the negative chamber.