[jeremy3220]

The fork is brand new... :| I find it odd some people have been reporting the same issue as me and some seem on par with fox recommendations (always has been the case for me from previous forks). What kind of service would the fork need? I have 0 knowledge on fork maintenance

I'm also using a digital pump, and I do cycle the fork to equalize every X of PSI, wait a bit for it to stabilize and repeat. I even check on how much PSI I loose when disconnecting the pump and compensate for that I doubt it's the pump but I'll try get readings from a few more pumps from friends.

Your fork doesn't lose pressure when you disconnect the pump, your pump does. When you connect it the fork pressurizes the pump, hence the drop in psi since you filled the fork.

 

[davec113]

might be time to pull it apart and make sure your negative chamber isn't full of grease. I know mine isn't because I rebuilt mine before even riding it. At 170lbs and 90psi and that puts me at 34mm sag in an aggressive position and about 30mm neutral over the bike so something is definitely not adding up. I'm using a digital pump so there is no chance of old analog gauge wear (which does happen I've had pumps be off more than 10psi after a year of use).

And just so we're all clear on how to inflate its pump up to x psi, leave pump attached and cycle fork to equalize chambers, check psi and repeat until psi is at desired value after cycling, disconnect pump.

Yup, this... I bet neg air chamber is blocked with grease.

I have a '20 Enduro S4, 170mm 38 Factory, about 205 lbs w/ gear. Factory recommended settings were right on for me, I run rebound a little faster though.

 

[Jesse Hill]

Ok two things. Just because it's new doesn't mean it was assembled right, there are multiple cases of both RS and Fox having excessive grease in the negative chamber. At around 6:40 you can get an idea of how it should be assembled vs what how they're assembled in a production line

second thing your setting your air wrong. If I'm understanding you correctly you are setting it let's just say for example you want 90psi so you set it 90psi and then re check and find it at 85psi so you think your losing 5 psi when you disconnect the pump so you set it to 95 to compensate. This is incorrect and you are actually setting your fork to 95. The air your losing is the air in the pump and hose, the Schrader valve on your fork is closed before the hose o ring is unsealed from the schrader stem. The lower psi your getting when re connecting is the air from your fork re filling the hose and pump.

 

[neur0x]

Your fork doesn't lose pressure when you disconnect the pump, your pump does. When you connect it the fork pressurizes the pump, hence the drop in psi since you filled the fork.

I understand that. But I've been told it still looses a tiny bit of air when unscrewing the hose from the valve. Guess I've been told wrong.

 

[neur0x]

Ok two things. Just because it's new doesn't mean it was assembled right, there are multiple cases of both RS and Fox having excessive grease in the negative chamber. At around 6:40 you can get an idea of how it should be assembled vs what how they're assembled in a production line

second thing your setting your air wrong. If I'm understanding you correctly you are setting it let's just say for example you want 90psi so you set it 90psi and then re check and find it at 85psi so you think your losing 5 psi when you disconnect the pump so you set it to 95 to compensate. This is incorrect and you are actually setting your fork to 95. The air your losing is the air in the pump and hose, the Schrader valve on your fork is closed before the hose o ring is unsealed from the schrader stem. The lower psi your getting when re connecting is the air from your fork re filling the hose and pump.

Indeed. I would expect a 1500€ fork to be assembled properly on such a simple task as applying grease.
Understood (see reply above). Something like that, difference isn't as large as 5 psi. 1/2PSI max.

Thanks for the advices guys, I'll certainly have someone service it ASAP.

 

[Jesse Hill]

I understand that. But I've been told it still looses a tiny bit of air when unscrewing the hose from the valve. Guess I've been told wrong.

Nope, there is no way for it to lose air. When connected the pump and fork are equalized and then when unscrewing the schrader valve closes first sealing the fork. Then the o ring in the hose unseat letting out the air in the hose.

 

[neur0x]

Nope, there is no way for it to lose air. When connected the pump and fork are equalized and then when unscrewing the a header valve closes first sealing the fork. Then the o ring in the hose unseat learning out the air in the hose.

Got it. Thx for the clarification!

 

[Paranoid_Android]

Nope, there is no way for it to lose air. When connected the pump and fork are equalized and then when unscrewing the schrader valve closes first sealing the fork. Then the o ring in the hose unseat letting out the air in the hose.

A shock definitely can lose pressure while disconnecting a shock pump in certain situations. I'm very heavy and run my Fox suspension at maximum pressure. Some pumps disconnect with no issue at all, others will cause the shock to lose in the order of 40psi even while disconnecting as quick as I can. The same pump on my Rockshox suspension (lower pressures) causes no loss at all. It's a loss that is measurable and can be tested. I totally understand the theory you mention, but the valve is not completely open or completely closed; it can be slightly open and with a low-volume high-pressure shock, that slight moment before the valve seals completely, is more than enough to release a substantial amount of air. The clearest way to test this is to very slowly unscrew the pump on a shock/pump combo that suffers this issue. If I do this, I can release the entire contents of the shock while disconnecting.

Note: This is completely seperate from the concept of losing some air pressure as the shock is fitted and becomes pressurised. There's several things going on here and they tend to be conflated which is why people like to say it definitely cannot happen or it definitely can.

 

[Jesse Hill]

A shock definitely can lose pressure while disconnecting a shock pump in certain situations. I'm very heavy and run my Fox suspension at maximum pressure. Some pumps disconnect with no issue at all, others will cause the shock to lose in the order of 40psi even while disconnecting as quick as I can. The same pump on my Rockshox suspension (lower pressures) causes no loss at all. It's a loss that is measurable and can be tested. I totally understand the theory you mention, but the valve is not completely open or completely closed; it can be slightly open and with a low-volume high-pressure shock, that slight moment before the valve seals completely, is more than enough to release a substantial amount of air. The clearest way to test this is to very slowly unscrew the pump on a shock/pump combo that suffers this issue. If I do this, I can release the entire contents of the shock while disconnecting.

Note: This is completely seperate from the concept of losing some air pressure as the shock is fitted and becomes pressurised. There's several things going on here and they tend to be conflated which is why people like to say it definitely cannot happen or it definitely can.

if this is happening then the o ring in your shock pump is worn out and flattened or its a poorly made pump and I would replace it. If designed right the o ring should engage well before the valve is depressed, you can test it by screwing on your pump until you feel on some resistance and then give the pump a few strokes and watch how incredibly fast you build psi (because you haven't depressed the valve). The schrader valve is also a spring loaded valve so once the mechanical needle is no longer pushing on the valve the valve will close regardless the fact that the psi is equal on both sides.

 

[Paranoid_Android]

if this is happening then the o ring in your shock pump is worn out and flattened or its a poorly made pump and I would replace it. If designed right the o ring should engage well before the valve is depressed, you can test it by screwing on your pump until you feel on some resistance and then give the pump a few strokes and watch how incredibly fast you build psi (because you haven't depressed the valve). The schrader valve is also a spring loaded valve so once the mechanical needle is no longer pushing on the valve the valve will close regardless the fact that the psi is equal on both sides.

I have various different pumps that all end up doing the same thing. Maybe it's more related to the shock valve than the pump? I was also under the impression that this just didn't occur but was advised otherwise by the suspension place that works on my bike. They mechanic for a top EWS rider and seem to know their stuff. I'm very much an amateur. I may not be explaining it well, understanding you correctly, or even understanding the valve mechanism itself; but my understanding was that the shrader valve of the shock isn't able to close fast enough to prevent a momentary air release. With lower pressures, that release is negligible. But with 350psi it's a decent amount.

 

[Jesse Hill]

I have various different pumps that all end up doing the same thing. Maybe it's more related to the shock valve than the pump? I was also under the impression that this just didn't occur but was advised otherwise by the suspension place that works on my bike. They mechanic for a top EWS rider and seem to know their stuff. I'm very much an amateur. I may not be explaining it well, understanding you correctly, or even understanding the valve mechanism itself; but my understanding was that the shrader valve of the shock isn't able to close fast enough to prevent a momentary air release. With lower pressures, that release is negligible. But with 350psi it's a decent amount.

think about it for a second if this were true then wouldn't you hear the same hiss of air while screwing on the pump until the o ring sealed? I'll bet you don't and you shouldn't because that is not how the system is designed. the point that depresses the valve sits lower in the pump head than the o ring so the o ring seals the interface first then the needled depresses the valve on install. on uninstall it is the exact opposite. so with that said where is this air going to escape to? if the fork chamber is 40psi and the pump is 40 psi there is no low side for the air to travel to and the valve simply shuts. then as you continue to unscrew the pump the o ring unseats and now you have 40 psi in the pump exposed to atmospheric and now you hear the hiss.

 

[Paranoid_Android]

think about it for a second if this were true then wouldn't you hear the same hiss of air while screwing on the pump until the o ring sealed? I'll bet you don't and you shouldn't because that is not how the system is designed. the point that depresses the valve sits lower in the pump head than the o ring so the o ring seals the interface first then the needled depresses the valve on install. on uninstall it is the exact opposite. so with that said where is this air going to escape to? if the fork chamber is 40psi and the pump is 40 psi there is no low side for the air to travel to and the valve simply shuts. then as you continue to unscrew the pump the o ring unseats and now you have 40 psi in the pump exposed to atmospheric and now you hear the hiss.

Your explanation sounds logical to me. Could it be that most pumps kinda suck and even when new, the o-rings fail to do their job? I haven't and won't try to argue how this is all supposed to work; just that I lose a significant amount of air when I disconnect all the pumps I have and the pumps the shop uses.

 

[Jesse Hill]

Your explanation sounds logical to me. Could it be that most pumps kinda suck and even when new, the o-rings fail to do their job? I haven't and won't try to argue how this is all supposed to work; just that I lose a significant amount of air when I disconnect all the pumps I have and the pumps the shop uses.

How are you verifying your losing air?

 

[Paranoid_Android]

How are you verifying your losing air?

Because it's such a large amount of air it's very obvious. The increase in sag is distinct. There's also the decrease in pressure that I see when reconnecting (above and beyond the loss from pressurising the pump). If I don't unscrew the pump super fast, I can release a lot of pressure. I'm sure if I did it very slowly I could release most or all of the air in the shock.

I feel like I've highjacked this thread more than enough. Apologies and I'll dip out!

 

[neur0x]

Well, "quick" air spring service and as expected there was way too much grease... I'm now running:

96 PSI - 87/88Kg fully geared (loosing weight)
1 token.
around 18% SAG
settings from fully closed:
HSC 6
LSC 10
HSR 3
LSR 4

Still needs tuning, this was basically setup in 2 runs of a loop but it already feels a massive improvement over before.

Some pictures:

Positive chamber:

Negative Chamber:

There was even more grease inside the air sleeve.

So, again, thx for the great tips about the negative air chamber and the terrible QC at FOX!!!

 

[retrofred]

Can having to grease in the negative chamber cause a knocking sound on larger impacts? I am chasing rattles and knocks on my 2021 Ransom 920. Most of the rattles were from cables in the downtube not being wrapped, but I have knocking that I can't quite put my finger on. I suspect it might be from the headset. I don't think it is seated correctly and it's also a cheap headset. Am planning on changing tomorrow.

 

[neur0x]

Can having to grease in the negative chamber cause a knocking sound on larger impacts? I am chasing rattles and knocks on my 2021 Ransom 920. Most of the rattles were from cables in the downtube not being wrapped, but I have knocking that I can't quite put my finger on. I suspect it might be from the headset. I don't think it is seated correctly and it's also a cheap headset. Am planning on changing tomorrow.

I'm don't think so. At least in my case there was no knocking just poor performance. I have a Scott Genius 2018 and had terrible rattle with the cables after a while that need to be sorted out. If you suspect it's the headset try and retighten it. Doesn't hurt to try.

 

[jeremy3220]

Can anyone comment on how to use a shaft clamp? I'm considering buying one to service my 38. I'm comfortable with servicing normal air springs but haven't done any work requiring a shaft clamp yet. The Fox 38 requires the lower bolt be removed from the shaft though. I guess my concerns are not clamping it tight enough and scratching the shaft when it twist or over clamping (or is that not possible?).

 

[Jesse Hill]

So the shaft clamps are made from a softer material than the shaft so it shouldn’t scratch. I actually prefer the rockshox ones because they are made from brass which is non marring (just like the non marring hammers and punches). The bolt isn’t on very tight so once you heat it it should not take much torque, if the shaft spins and you feel you didn’t put much leverage on then tighten the vice a little at a time and eventually it’ll hold.

 

[294037]

So the shaft clamps are made from a softer material than the shaft so it shouldn't scratch. I actually prefer the rockshox ones because they are made from brass which is non marring (just like the non marring hammers and punches). The bolt isn't on very tight so once you heat it it should not take much torque, if the shaft spins and you feel you didn't put much leverage on then tighten the vice a little at a time and eventually it'll hold.

This is good advice, I also recommend using good clamps, and clean both surfaces with iso to ensure decent grip.

you can crush or slip on the shaft for sure, and I always try to clamp in a zone that is less likely to be sliding through a seal or anything like that.