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  1. #1
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    Fox CTD shock 2013 issues

    Bought a SB95 frame back in Nov that came with a 2013 CTD trail adjust shock on it. At 10hrs, I noticed it had sucked a very small amount of air into the damper, audible but no noticeable loss in damping. At 25 hrs, it was getting worst and I could then feel the lossin in damping with the lean on the seat test. Finally sent it off for warranty rebuild at 35hrs. Fox replaced the shaft seal, pp spring, small pp shims, and the air can seals.

    2 weeks later, got it back and after the first 1hr of trail time, I could already hear air in the oil again. Now, at a whopping 4hrs, I can feel a loss in damping. To say I'm frustrated is an understatment at best.

    This is my first experience with a Fox boost valve shock. What gives here? Am I just extremely unlucky or are these shock notorious for sucking air due to the lower IFP pressures? It's a 175 bv tune. I've been running 155psi in the spring and ride in Descend mode 99% of the time.

  2. #2
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    I don't have an answer to your question, but what are the signs/symptoms of sucking air into the damper?
    Alcohol may lead nowhere, but it sure is the scenic route!

  3. #3
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    Hi,
    I have issue with my 2013 Fox Float CTD Evolution 8.5x2.5 shock that has ID CCZ9, compression tune is L and climb tune is F, it came on Santa Cruz Heckler frame and has no Boost valve or trial adjust.
    My first impression from the first ride that in climb mode the shock is completely closed and a 6” frame climbing like a hard tail.
    I take the bike to our local Fox service center and asked them if any option or calibration available to do it little more plushy at climb mode, and I get the answer “yes” and they can reduce some pressure of Nitrogen gas from the shock to get it work plusher in climb mode, for my mistake I agreed to this and now I have some issue with it.
    When I descending on fast downhill tracks with some jumps and technical areas with small bumps I hear a very strong metallic noise like air hummer strike from a shock, its sounds at the beginning of a suspension or like very fast rebound I don’t know how to explain this.
    I already take a shock two additional times to the service center and they try to play with the pressure of nitrogen gas, increase or decrease and nothing, I ask them also what exact pressure value need to be placed in this shock 175psi/200psi or maybe 225psi and they don’t know to answer me.
    May be some one here on MTBR can advise, what exact values of nitrogen charge need to be put inside a shock for optimal performance on my bike.
    Thanks

  4. #4
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    vadimn, the "boost valve tune" should be labeled on the air can of your shock. That number is the ifp pressure. Do you know where the guys at Fox set your ifp pressure when you asked them to soften it? I don't know what the acceptable range is for a inline shock, but most I've seen are between 150 and 200.

    Just a theory, but if they went low on the ifp pressure, the noise you are hearing could be the boost valve slamming open during hsc.

    Before you changed the ifp pressure, did you try using trail mode? You are really comprising the overall shock performance if you lower the ifp trying to get plushness in climb mode.

  5. #5
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    ktm520, thanks for reply.
    Evolution Series line of the Fox Float CTD Shocks has no boost valve, it some cheaper (OEM) version, Boost Valve only available on Factory Series shocks.

    My shock worked fine in Trial and also Descend modes before they play with nitrogen pressure. Now in both of modes I can hear this metal noise, its looks like very fast rebound or some think like this but I have no idea what is this and also guys from Fox have no idea too.

  6. #6
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    My bad, I missed that it is an Evolution shock. In that case, changing the ifp pressure is not what you want and it will make very little difference. The ifp should be around 400psi for your shock regardless of tune. The new CTD's are basically the same internally as an RP with a different lsc adjuster.

    Did you make sure that the shock eyelet bolts are tight?

  7. #7
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    Quote Originally Posted by ktm520 View Post
    Bought a SB95 frame back in Nov that came with a 2013 CTD trail adjust shock on it. At 10hrs, I noticed it had sucked a very small amount of air into the damper, audible but no noticeable loss in damping.
    I am having the same problem, shock has under 25hrs of riding (bought at end of February). I've had the same problem on a DHX Air. I'll send it to warranty, to see if it gets better. I wish we could change the IFP pressure like in the Rock Shox Monarch...
    Keith Scott: If you want to go mountain biking, then throw a leg over a new Banshee and the bike will do the talking

  8. #8
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    Quote Originally Posted by vadimn View Post
    ktm520, thanks for reply.
    Evolution Series line of the Fox Float CTD Shocks has no boost valve, it some cheaper (OEM) version, Boost Valve only available on Factory Series shocks.

    My shock worked fine in Trial and also Descend modes before they play with nitrogen pressure. Now in both of modes I can hear this metal noise, its looks like very fast rebound or some think like this but I have no idea what is this and also guys from Fox have no idea too.
    It sounds like what you are experiencing is cavitation on hard hits. Cavitation is caused by the pressure required to force oil through the piston fast enough to fill the space behind it, being lower than the actual pressure in front of the piston (which is determined by the IFP pressure). It often feels like a jarring/spiking sensation followed by a brief moment of zero rebound damping, often followed by another "slapping" sensation as the piston hits the oil behind it during the rebound stroke. This all happens VERY quickly and can easily feel like a single jarring event.

    This is specifically caused by an IFP pressure that is too low - it should be 400psi. The reason Boost Valve Floats can run lower pressure in the IFP is because the BV will open fully once the pressure behind it drops sufficiently (rather than requiring the pressure in front of it to climb hugely), which means cavitation is far less of an issue - this does not happen in the same manner with shims. All the harshness in the climb mode (which realistically is a complete lockout) is to do with the valving, not the IFP pressure - the options available to you are basically either making more use of the Trail mode, or getting the thing revalved.
    VorsprungSuspension.com - fully engineered suspension retuning & servicing in Whistler, BC.

  9. #9
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    Thanks Steve,
    We actually rebuild a shock yesterday with new seals and 26Bar of IFP pressure.
    I am going to a test ride and will post here later.

  10. #10
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    I have a non Boast Valve CTD shock which I bought when they first came out last year. Didn't put a lot of time on it last year.
    On today's ride, it started making the slurp noise and would occasionally feel like it would fall through the travel.
    Now to decide whether to send it to Fox for warranty or off to Push

  11. #11
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    Ok guys,
    After we rebuild a shock and fit 26bar in IFP, I still have more or less the same issue, may be less then more from a beginning but I still can hear kind of jarring event that Steve talking about it.
    My question is - is it possible to put 400PSI? Guys from Fox Service Center thinking that I am sick / crazy person...

  12. #12
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    Quote Originally Posted by vadimn View Post
    My question is - is it possible to put 400PSI? Guys from Fox Service Center thinking that I am sick / crazy person...
    Yes, that specification is directly from Fox. I think you may want to find a new service center. 26bar=377psi, so you weren't to far from 400.

  13. #13
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    Yeah, I know, all of us having issues and returns to this service center for more that 2,3,4 and some times 5 times to solve issue or tuning after shock service.
    This service center located 10 to 30 minutes in car from us, we have another service center much better from this but it located 2 hours driving from my location.
    So, better to buy some CCDB Air or Rock Shox .

  14. #14
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    I'm gonna chime in here because I have a separate issue but want to keep this thread alive too. I have a year-old (2013) Giant Trance X29 with the Boostvalve CTD shock. About 1 month after owning the bike the shock leaked oil more than normal out the seals. Lbs sent it off and I got the bike back 2 weeks later with a shock that looked to have an extensive rebuild by Fox, according to the work order that accompanied it. Fox claimed in the w/o that the oil disbursement was 'normal' but that they serviced it anyways. I know they did something with the CTD lever because it was crisp-acting when I got it back. Before that, it was kinda loose in the C or D modes.

    Fast-forward about 1 year and the shock has no discernible actuation feel in C,T, or D. Pedal bob is pretty bad and I have replaced the seals myself, thinking this was the cause. I'd like to think a simple seal replacement could not have caused this CTD to malfunction but the shock felt great after I serviced the seals. Now I'm getting pedal-bob and the a$$ end of the bike feels like it's dragging. I also have the air pressure set to provide normal sag (about 25%) and the rebound seems to be working ok.

    I'm looking for suggestions here. The shock is out of warranty but I'm divided between sending it to PUSH or sending it back to Fox and risking them just giving it a lick and a promise. Right now I have very little confidence in Fox.
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  15. #15
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    Quote Originally Posted by MTBeing View Post
    I'm gonna chime in here because I have a separate issue but want to keep this thread alive too. I have a year-old (2013) Giant Trance X29 with the Boostvalve CTD shock. About 1 month after owning the bike the shock leaked oil more than normal out the seals. Lbs sent it off and I got the bike back 2 weeks later with a shock that looked to have an extensive rebuild by Fox, according to the work order that accompanied it. Fox claimed in the w/o that the oil disbursement was 'normal' but that they serviced it anyways. I know they did something with the CTD lever because it was crisp-acting when I got it back. Before that, it was kinda loose in the C or D modes.

    Fast-forward about 1 year and the shock has no discernible actuation feel in C,T, or D. Pedal bob is pretty bad and I have replaced the seals myself, thinking this was the cause. I'd like to think a simple seal replacement could not have caused this CTD to malfunction but the shock felt great after I serviced the seals. Now I'm getting pedal-bob and the a$$ end of the bike feels like it's dragging. I also have the air pressure set to provide normal sag (about 25%) and the rebound seems to be working ok.

    I'm looking for suggestions here. The shock is out of warranty but I'm divided between sending it to PUSH or sending it back to Fox and risking them just giving it a lick and a promise. Right now I have very little confidence in Fox.
    The CTD shocks use a pressure sensitive piston that relies on the nitrogen gas to produce compression damping, but a shimmed system on rebound. Over time you get both a break down of the damping fluid as well as a drop in the gas pressure in the shock which cause the shock to develop a softer feel on the compression stroke. Basically, what you're describing is normal and a sign that you're in need of service.

    If you are considering us, we have a pretty great deal going through the end of this month! And hey, maybe you'll be the lucky winner and can get yourself setup with a spare shock for your bike!

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  16. #16
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    Quote Originally Posted by MTBeing View Post
    Fast-forward about 1 year and the shock has no discernible actuation feel in C,T, or D. Pedal bob is pretty bad and I have replaced the seals myself, thinking this was the cause. I'd like to think a simple seal replacement could not have caused this CTD to malfunction but the shock felt great after I serviced the seals. Now I'm getting pedal-bob and the a$$ end of the bike feels like it's dragging. I also have the air pressure set to provide normal sag (about 25%) and the rebound seems to be working ok.

    I'm looking for suggestions here. The shock is out of warranty but I'm divided between sending it to PUSH or sending it back to Fox and risking them just giving it a lick and a promise. Right now I have very little confidence in Fox.
    As Darren stated above, your shock just needs a damper service. You have ridden the shock for a year, and this is completely normal. It is not Fox's fault. They specify that damper service should be done every 100hrs of riding, or once a year. You should just send it to Push.

  17. #17
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    Fox CTD shock 2013 issues

    Looks like it's PUSH. Thanks Darren and Matty. You're right on with the squishy feeling.
    Please donate to IMBA or your local chapter. It's trail karma.

  18. #18
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    Quote Originally Posted by ktm520 View Post
    Bought a SB95 frame back in Nov that came with a 2013 CTD trail adjust shock on it. At 10hrs, I noticed it had sucked a very small amount of air into the damper, audible but no noticeable loss in damping. At 25 hrs, it was getting worst and I could then feel the lossin in damping with the lean on the seat test. Finally sent it off for warranty rebuild at 35hrs. Fox replaced the shaft seal, pp spring, small pp shims, and the air can seals.

    2 weeks later, got it back and after the first 1hr of trail time, I could already hear air in the oil again. Now, at a whopping 4hrs, I can feel a loss in damping. To say I'm frustrated is an understatment at best.

    This is my first experience with a Fox boost valve shock. What gives here? Am I just extremely unlucky or are these shock notorious for sucking air due to the lower IFP pressures? It's a 175 bv tune. I've been running 155psi in the spring and ride in Descend mode 99% of the time.
    We at Avalanche Suspension have a solution to the CTD/RP23 Float shocks. We remove the Boost Valve and convert it to a speed sensitive damper (SSD). This is done by converting the Boost Valve system to a valving shimmed compression system. This allows us to reduce the pressure on the IFP to normal shock pressures increasing the life of the oil and nitrogen charge. The SSD system provides for better performance on high speed square edged hits and can be custom tuned for any linkage curve or rider preference. We have also modified the internal compression adjuster system to our high speed blow-off (HSB) system, The low speed circuit is converted to our HSB system, this allows for increased low speed compression that blows off on small bumps and creates high speed threshold adjustment without harshness in the high speed circuit, we can tune this up or down depending on the adjustment range you are looking for.

    Check it out here:Float CTD and RP23 SSD Modifications

  19. #19
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    Thanks Craig. I revlaved the rebound in the ctd (big improvement) and played with different ifp settings, but it still spikes on square edge, which I can't tune out of it without a higher flow piston. I've been meaning to look and see what you all have to offer for the float shocks. Right now, I'm torn between getting a Monarch RT or + and revalving it myself, or sending off the ctd for a Avalanche/Push tune.

    Can you expound a little more on the HSB system? Doesn't sound much different than the varying spring loaded poppet valve Fox already uses. What exactly do you mean by "high speed threshold adjustment"? I like the idea of increased lsc without increased harshness but isn't that kind of the holy grail of offroad suspension?

  20. #20
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    Quote Originally Posted by ktm520 View Post
    Thanks Craig. I revlaved the rebound in the ctd (big improvement) and played with different ifp settings, but it still spikes on square edge, which I can't tune out of it without a higher flow piston. I've been meaning to look and see what you all have to offer for the float shocks. Right now, I'm torn between getting a Monarch RT or + and revalving it myself, or sending off the ctd for a Avalanche/Push tune.

    Can you expound a little more on the HSB system? Doesn't sound much different than the varying spring loaded poppet valve Fox already uses. What exactly do you mean by "high speed threshold adjustment"? I like the idea of increased lsc without increased harshness but isn't that kind of the holy grail of offroad suspension?
    The spikes will smooth out if you remove the boost valve and replace it with shims, then the IFP settings will not be critical and a standard pressure will work. Lets just say we have found the holy grail of suspension! No, basically what everyone wants their suspension to feel like is to have low speed compression that holds the shock up and is plush on small bumps, not bottom and slice through squared edged bumps. If you add a valve the stays closed long enough to provide low speed compression for pedaling(threshold), but has the ability to open a predetermined amount (float) and can blow-off at a controlled rate(high speed blow-off, HSB) and then the shim stack can then blend in to control the entire stroke, then I guess this would be the holy grail. We try to accomplish this by using one of 3 different rate springs that are the proper length to determine the correct preload, rate of blow-off, float (free length to solid height) to get the desired affects. So yes it is sort of how the Fox system works we just re-engineered it to do what we want it to do.

    We have a similar system we use in our fork cartridge system described here:Floating Valving Assisted Threshhold High Speed Blow-off System

  21. #21
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    Gotcha. My gears were spinning off in a more elaborate direction that was trying to envision how you would completely redesign that circuit. I wouldn't have thought that the bleed circuit would flow enough oil to affect hsc but it sounds like it's more for controlling the transition to the shim stack. I had a looked for a source for the small poppet spring but it wasn't cost effective for small quantities.

    I just read your FAQ page. Very informative. I was under the impression that the stock piston wouldn't flow enough oil. Thanks for the feedback.

  22. #22
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    Subscribed! I want to keep an eye on where this thread is headed. The last few posts are very interesting.

    Also, Craig, you need to post on here more.

  23. #23
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    Quote Originally Posted by mullen119 View Post
    Subscribed! I want to keep an eye on where this thread is headed. The last few posts are very interesting.

    Also, Craig, you need to post on here more.
    I will as needed, I do follow these forums very closely.

  24. #24
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    Looks like it's PUSH. Thanks Darren and Matty. You're right on with the squishy feeling.
    10-4. If you have any questions, feel free to drop us an email or phone call.

    We remove the Boost Valve and convert it to a speed sensitive damper (SSD).
    I think it's important to point out that the stock FOX Boost Valve from the factory is speed sensitive. For that matter, every MTB fork damper and rear shock is. What makes the stock FOX Boost Valve piston assembly unique is that it provides a secondary component that is also position sensitive in addition to the speed sensitivity.

    Darren

  25. #25
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    Quote Originally Posted by PUSHIND View Post
    10-4. If you have any questions, feel free to drop us an email or phone call.

    I think it's important to point out that the stock FOX Boost Valve from the factory is speed sensitive. For that matter, every MTB fork damper and rear shock is. What makes the stock FOX Boost Valve piston assembly unique is that it provides a secondary component that is also position sensitive in addition to the speed sensitivity.

    Darren
    Yes, but is it really speed sensitive enough? oil is oil now, I guess!

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