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Discussion Starter · #1 ·
My rear shock loses air while I ride. It will not lose any air while static, in fact it just sat for two weeks unused and held pressure.

What could be causing this and what can I do about it?


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Explain exactly "how" it's loosing air. As you ride and use it, does it feel softer and softer, or does it just happen to sit further into the travel, but feel kind of similar? Could be one of several things, as said if you've managed to nic the stanchion/shaft, then when the shock goes through it's travel, it could let air escape. What I was asking about is positive air migrating into the negative chamber, which can also happen for one of several reasons and feel like the shock is loosing air, when in fact it's just going from the POS to the NEG and sucking it into it's travel.
 

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viva la v-brakes!
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Discussion Starter · #5 ·
Explain exactly "how" it's loosing air.
It seems to lose air over the course of a ride. Lost about 58psi last night on an easy 72-minute ride. It feels softer and softer as I go.

Just filled it back up and cycled the shock about two dozen times and it didn't loose much/any air pressure, to 'bleed' into the negative air chamber.

I do have a nick on the stanction, pictured below, it's not as bad as it looks, pretty smooth. But I suppose it could be an issue.



My LBS overhauled the shock this winter. Maybe they didn't get it quite right so it's failing prematurely?

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That nick might be high enough to contact you're lower air can seals. Could be allowing some pressure to slowly escape, might want to consider filling it with some jb weld or even nail polish if it's shallow enough. File down any high spots.

That's a nasty nick.
 

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That's a nasty gouge, not a nic. Only way to know that that's not causing the issue would be to pump the shock up harder than you would normally run it so it can't get that far into the travel and/or add a volume spacer to help ramp up quicker, but to me that's probably where you're loosing air if you regularly push the o-ring there - and you would if you keep loosing pressure. As Eshew said, best bet would be to put some nail polish or other on it and then carefuly make sure it's even with the rest of the body (if it's high it could also cause issues).

I'd pump it up at least 25-30% over what you would normally ride to restrict travel, that's the easiest way to test it. If you never get the o-ring down to the gouge and it still looses air, then your air seals need replacing, could be the shop nicked one when servicing and worse yet, nicked the inside of the air can, but do the simple more pressure and ride test first before you go into the shock.
 

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viva la v-brakes!
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Discussion Starter · #8 ·
Hmm,

That nick has been there well over a year. Haven’t had a problem until recently. But perhaps it was slowly wearing away at the seal?

I guess I’ll try riding it with higher pressure and see how it goes. However, my ride last night was pretty mild. I intentionally landed hard once to bottom out the shock, that’s what put the o-ring where it is. But other than that, I doubt I was using enough travel to push the seal down over the gouge... at least until after I started losing air.

I would have a hard time making it any smoother than it is, whether with a file or even nail polish, I am pretty sure I would only make it worse. What would be another option? Replacing that shaft (shock body?) or am I looking at a whole new shock at that point?


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I'll just mention that the seals on fork stanchions don't hold air. Air pressure is contained inside the stanchion and held there by the top cap and seal around the air shaft at the bottom of the stanchion. So, scratches and gouges on a fork stanchion won't cause pressure loss. In shocks, the stanchion is also the air shaft, so the seal inside the base of the air can has to seal against the outside of the stanchion to hold air. That air seal is just inside the dust seal that visible on the outside of the air can. If that seal passes over scratches or gouges in the stanchion, air pressure will be lost.
 
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