If I bleed the air out of my Fox Float CTD rear shock it sucks down. Is this normal or an indicator of the negative spring starting to fail?
Shock the Fox CTD do this?
- Thread starter profro
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But, should it suck down like that when bleeding air from the can?
Don't you?
Yes, I mean yes.
Yes is what I meant to say. That's normal. It's the pressure in the negative spring pulling it down. You can avoid this if cycle it after letting some air out, and do that a few times. If you're trying to work on the air can or get inside the shock, emptying out the negative chamber helps get the can off.
No it should not.... Be very careful if you take it apart because the air can will blow off harder than a pro-core tire! The trick is to put a heavy cloth shop rag through the lower shock eyelet as you unscrew the can. This will block the can from flying off, and still aim it away from your face.
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OK, I couldn't find the keyword to search for but finally found it. Fox refers to it as "stuck down" I found this on their website.
WARNING: Never attempt to pull apart, open, disassemble, or service a FOX shock that is in a "stuck down" condition. A "stuck down" condition results from a failure of the dynamic air seal (located between the positive and negative air chambers within the shock air sleeve), resulting with the negative chamber retaining a higher pressure than the positive chamber. To test whether the shock is in fact "stuck down":
WARNING: Never attempt to pull apart, open, disassemble, or service a FOX shock that is in a "stuck down" condition. A "stuck down" condition results from a failure of the dynamic air seal (located between the positive and negative air chambers within the shock air sleeve), resulting with the negative chamber retaining a higher pressure than the positive chamber. To test whether the shock is in fact "stuck down":
- Remove the air cap and depress the Schrader valve, to completely release air pressure from the positive chamber of the shock.
- If your shock has an EVOL air sleeve, you must release air pressure slowly to stop from inducing a "stuck down" condition.
- If the shock body retracts into the air sleeve near bottom-out after the air is slowly released from the positive chamber, attach a FOX high pressure pump and pressurize the shock to 250 psi/ 17 bar).
- If your shock has an EVOL air sleeve, you must cycle the shock after every 50psi addition while filling.
- If the shock does not fully extend, it is in a "stuck down" condition.
I don't have this condition, Normal air can pressures extend shock to full length. Its only when I bleed air down to less than 50psi that the shock retracts by 10-15mm. As suggested by Kidwoo, if I cycle the shock it returns to full length.
Getting stuck down is when the shock gets out of equilibrium with the negative chamber. Usually just deflating it and 'resetting' everything fixes it.
But if your shock doesn't compress to a point where the air spring passes the exchange port (it's a little dimple on the main air can) when you deflate it, then you still have a pressurized negative chamber, with nothing in the main one. So it compresses.
It's normal. While not as bad as the stuck down situation, that means your negative chamber is still pressurized. Like I said, if you're deflating it to work on it, cycle it so that you pass that exchange port and send some air back into the main can.
But if your shock doesn't compress to a point where the air spring passes the exchange port (it's a little dimple on the main air can) when you deflate it, then you still have a pressurized negative chamber, with nothing in the main one. So it compresses.
It's normal. While not as bad as the stuck down situation, that means your negative chamber is still pressurized. Like I said, if you're deflating it to work on it, cycle it so that you pass that exchange port and send some air back into the main can.
As long as it's not retracting all the way and/or quite forcefully you're probably fine. It helps to cycle the shock (force it to top out while at low pressure and still in the frame) a few times before trying to remove the can, to ensure the negative chamber pressure is fairly low.
As 4130biker said though it's not a bad idea to put a rag through the eyelet and aim it away from yourself when pulling the can off, just to be safe.
As 4130biker said though it's not a bad idea to put a rag through the eyelet and aim it away from yourself when pulling the can off, just to be safe.
I was reading stuck down, not sucked down. Too early, no coffee