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  1. #1
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    Fox CTD "O/C" Evolution damper service info and pics

    Just did a service on a CTD fork for the first time. This one has the CTD "O/C" damper which is the cheaper version than the FIT one, I gather. The Foxracingshox.com service site has info on bleeding the oil out of the trail adjust and remote lockout versions through the bleed port.

    The CTD O/C (Open Cartridge?) damper doesn't have any bleed port, and the compression adjustment shaft goes all the way through the damper unit, unlike the older FIT forks from which you could just remove the compression adjuster to bleed the damper.

    Don't do what I did and remove the circlip and spring from the top of the damper, it's very fiddly to get back on.

    Pull the damper head out of the cartridge using your 26mm socket, the thread is a standard thread unlike the Rockshox units:



    Once you've got the CTD adjust knob off the top you'll see a stack with a tiny circlip at the top, then a washer, then a spring, then a larger washer. Underneath this is the spring and ball for the CTD detents. There's no need to remove this assembly unless you need to replace the ball or spring.



    The bottom of the damper has a small bolt which holds on a wing-shaped plate that covers the ports for the C, T and D settings.

    Climb setting (small and large ports closed):



    Trail setting (small port closed, large port open):



    Descend seting (small and large ports open):



    If you remove the spring and circlip assembly from the top of the damper, the easiest way to get them back on is to undo this small bolt from the bottom (marking which way the wing plates are aligned on the 4-sided shaft), push the shaft up through the top, and reassemble without any need to compress the top spring while putting the circlip back on (a 4-handed operation).

    Refill the damper with 82.5cc of Fox red, test the CTD functions and reinstall.

    Drawings from Foxracingxhox:

    32 mm 29 120-130 FLOAT O/C CTD Cartridge Assembly

    32 mm 26/29 FLOAT O/C CTD Cartridge: Subassemblies

    Have fun everyone!

    - Joel
    Attached Thumbnails Attached Thumbnails Fox CTD "O/C" Evolution damper service info and pics-ctd-oc-1.jpg  

    Fox CTD "O/C" Evolution damper service info and pics-ctd-oc-2-descend.jpg  

    Fox CTD "O/C" Evolution damper service info and pics-ctd-oc-3-trail.jpg  

    Fox CTD "O/C" Evolution damper service info and pics-ctd-oc-4-climb.jpg  

    Fox CTD "O/C" Evolution damper service info and pics-ctd-oc-5-top.jpg  

    Cycling is Serious Business.

  2. #2
    "El Whatever"
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    Man, thanks for sharing.

    Did you noticed if the compression and rebound pistons have shims?

    Thanks again!
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  3. #3
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    Hey Joel,

    Just came across your post, having started my own thread yesterday asking advice about changing the oil in this damper.

    Could you tell me how you drained the oil from the O/C damper, and how you refilled with new oil? Is it a 'sealed' unit like a FIT cartridge, or like the open bath dampers I'm familiar with?

    As you said, no instructions on the Fox web site for the O/C damper, so I'd kinda like to know what I'm getting myself in for before I dismantle this baby... Thanks.

  4. #4
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    Quote Originally Posted by Warp View Post
    Man, thanks for sharing.

    Did you noticed if the compression and rebound pistons have shims?

    Thanks again!
    You've probably found one by now, but just for completing the thread. There are shims on the comperssion damper, but how stiff they are I'm not entirely sure. The size of the ports suggest orifice choke damping.

    Rebound is not shimmed.

    Quote Originally Posted by PerthMTB View Post
    Hey Joel,

    Just came across your post, having started my own thread yesterday asking advice about changing the oil in this damper.

    Could you tell me how you drained the oil from the O/C damper, and how you refilled with new oil? Is it a 'sealed' unit like a FIT cartridge, or like the open bath dampers I'm familiar with?

    As you said, no instructions on the Fox web site for the O/C damper, so I'd kinda like to know what I'm getting myself in for before I dismantle this baby... Thanks.
    Just for the others who stumble across this thread:
    Think manitou TPC cartridge, but with bleed holes so if the damper is over-filled they spew the excess damper oil into the bushing lube oil. Test full stroke on the bench before putting the damper back in.
    Which explains why the oil you drain from the damper leg will always look mixed.
    There is a valve arrangement on these bleed ports. Presumably so the oil doesn't leak into the lower legs when the fork is inverted or lying flat.

    A clunky mid-stroke change in these forks means not enough oil or air in the oil. Air will obviously stroke it's way up and out but insufficient oil won't.
    Owner of www.shockcraft.co.nz and NZ Manitou Service Agent.
    www.dougal.co.nz Suspension setup & tuning.
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  5. #5
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    Quote Originally Posted by Dougal View Post
    You've probably found one by now, but just for completing the thread. There are shims on the comperssion damper, but how stiff they are I'm not entirely sure. The size of the ports suggest orifice choke damping.

    Rebound is not shimmed.



    Just for the others who stumble across this thread:
    Think manitou TPC cartridge, but with bleed holes so if the damper is over-filled they spew the excess damper oil into the bushing lube oil. Test full stroke on the bench before putting the damper back in.
    Which explains why the oil you drain from the damper leg will always look mixed.
    There is a valve arrangement on these bleed ports. Presumably so the oil doesn't leak into the lower legs when the fork is inverted or lying flat.

    A clunky mid-stroke change in these forks means not enough oil or air in the oil. Air will obviously stroke it's way up and out but insufficient oil won't.
    Actually I don't think there are valves on the bleed holes. I know when I left mine upside down for 10 mins I lost damping in the first part of the stroke consistent with with a loss of damper oil. This wasn't a temporary loss of damping straight after being upside down. It was permanent until I next serviced it and replaced the oil.

    That was one of the many reasons why I sold it.

  6. #6
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    I hang mine upside down frequently and never have had an issue.

    The shim on the base valve is purely a hsc blowoff for Climb. It is preloaded with a stiff coil spring. Port orifices all around in this jewel. I have a '14 120. It spikes terribly in T and D is too soft for anything but a sunday drive.

  7. #7
    rgf
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    Quote Originally Posted by Dougal View Post
    Which explains why the oil you drain from the damper leg will always look mixed.
    There is a valve arrangement on these bleed ports. Presumably so the oil doesn't leak into the lower legs when the fork is inverted or lying flat.
    Hello, I have a float 32 o/c. Yesterday I did the second lower leg service of its life.
    The first time I was a bit puzzled to find the damper side oil kind of yellowish when I drained it but I just thought it was old, cleaned everything, put the correct Fox Green quantity and the fork worked fine.

    This time it was even more yellow, and I just serviced it three months ago. I did the usual lower leg (and air shaft) service, left the cartridge unchanged. The first strokes the damping was completely absent (C mode didn't lock it out at all), then it looks like it sucked some oil in and started working but it still doesn't lock out as before and even rebound isn't working properly.

    Is it really that normal to find mixed damping and lubrication oil in the right lower leg? Given that the fork has less than a year, should I send it for warranty?
    I thought I could threat this damper like a sealed cartridge and just change the lubrication oil but it looks like it's leaking the damping oil in the lower leg.
    Last edited by rgf; 07-23-2014 at 08:00 PM.

  8. #8
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    Quote Originally Posted by rgf View Post
    Hello, I have a float 32 o/c. Yesterday I did the second lower leg service of its life.
    The first time I was a bit puzzled to find the damper side oil kind of yellowish when I drained but I just thought it was old, cleaned everything, put the correct Fox Green quantity and the fork worked fine.

    This time it was even more yellow, and I just serviced it three months ago. I did the usual lower leg (and air shaft service), left the cartridge unchanged. The first strokes the damping was completely absent (C mode didn't lock it out at all), then it looks like it sucked some oil in and started working but it still doesn't lock out as before and even rebound isn't working properly.

    Is it really that normal to find mixed damping and lubrication oil in the right lower leg? Given that the fork has less than a year, should I send it for warranty?
    I thought I could threat this damper like a sealed cartridge and just change the lubrication oil but it looks like it's leaking the damping oil in the lower leg.
    I'd be tempted to try wrapping a road bike inner tube section around those bleed holes to keep the oil in the cartridge.

    I don't understand this design at all. I have no idea what they were thinking.
    Owner of www.shockcraft.co.nz and NZ Manitou Service Agent.
    www.dougal.co.nz Suspension setup & tuning.
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  9. #9
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    Quote Originally Posted by rgf View Post
    Hello, I have a float 32 o/c. Yesterday I did the second lower leg service of its life.
    The first time I was a bit puzzled to find the damper side oil kind of yellowish when I drained it but I just thought it was old, cleaned everything, put the correct Fox Green quantity and the fork worked fine.

    This time it was even more yellow, and I just serviced it three months ago. I did the usual lower leg (and air shaft) service, left the cartridge unchanged. The first strokes the damping was completely absent (C mode didn't lock it out at all), then it looks like it sucked some oil in and started working but it still doesn't lock out as before and even rebound isn't working properly.

    Is it really that normal to find mixed damping and lubrication oil in the right lower leg? Given that the fork has less than a year, should I send it for warranty?
    I thought I could threat this damper like a sealed cartridge and just change the lubrication oil but it looks like it's leaking the damping oil in the lower leg.
    That's exactly what happened with mine. The lock out stopped working properly and the rebound became inconsistent. I was very disappointed with my evo fork.

  10. #10
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    Oil shouldn't leak out of the holes when inverted or during use. I'd be looking at the shaft seal if damper oil is getting in the bath oil.

  11. #11
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    Quote Originally Posted by ktm520 View Post
    Oil shouldn't leak out of the holes when inverted or during use. I'd be looking at the shaft seal if damper oil is getting in the bath oil.
    What is stopping the oil leaking out the holes when the fork is inverted?

  12. #12
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    An unsubstantiated theory. There are 4 small holes around the top of cartridge.

  13. #13
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    The first gen of these cartridges had no holes (as per the one in my pics from last year). I don't think they had the spring loaded pressure relief valve in the plastic base/rebound assembly either. As a result, when the pressure spiked they exploded! No surprises there. The circlip holding in the plastic base assembly was usually the thing to break apart.

    The second gen which were issued as warranty replacements had holes drilled in the top, 4 of them, about 2mm. I personally theorise that these were just returned cartridges which had been drilled and then sent back out to customers until a better solution could be engineered.

    The later ones I've seen have had no bleed holes in the top, but a spring and ball arrangement in the plastic base assembly which serves as a blow-off valve in case of spiking pressure.

    All in all, the cartridge design is pretty crappy, with the bladder-type FIT cartridges being a much better product.

    I've had Evolution cartridges which were overfilled from the factory, as and such the damper only got half travel, as well as some which were under filled giving no damping in the bottom part of the stroke.

    There is nothing stopping the oil leaking from the holes when the fork is inverted. If you do the drilling mod yourself to a cartridge which Fox won't warranty but which is leaking due to pressure, one or two smaller holes should suffice and will slow down the leaking.

    - Joel
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  14. #14
    rgf
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    Too bad I just sent it for a warranty service, now I'm curious which cartridge gen I had... let's hope they will just put a FIT cartridge there and ditch this crappy o/c one.
    I find it irritating that the cartridge needing to be serviced more often has little to none docs about it.

    Thinking about selling it when it gets back from service.

  15. #15
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    Re: Fox CTD "O/C" Evolution damper service info and pics

    Quote Originally Posted by tomacropod View Post
    All in all, the cartridge design is pretty crappy, with the bladder-type FIT cartridges being a much better product.
    I'll second that!

    My Evo came on a '14 Scott. It has the 4 holes up top, but I recall some type of check valve when I had it apart. It hangs upside down most of the time and has never lost oil.

  16. #16
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    Actually,the fork cartridge I posted pics of was from '13 MY bike.

  17. #17
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    Thanks for the clarification people. It seems that there's different versions of this cartridge. Mine was a 2014 fork on a giant trance. It definitely had no valves or anything to prevent oil leaking out the holes. Sounds like they've fixed this on some forks.

  18. #18
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    Can someone post a picture of the holes that you are talking about? I've got a Evo 26 150 2013 I'm about to service for the first time. Thanks for all the info.

  19. #19
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    They're nothing you need to consider in your servicing. Just remove the damper head as per the first pic. There may or may not be a couple of holes just below the bottom of the thread, above the damper head in the air space above the damper oil.

    Refill it with fox red when you go to reassemble it. Actually, it probably doesn't matter what oil you use in this crappy damper, it will still be crappy.

    - joel
    Cycling is Serious Business.

  20. #20
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    Serviced my Evo fork this weekend. Piece of cake thanks to Tomacropod's post. I took the dampener cartridge completely out as well as the air spring piston, then reassembled it using mobile 1 ATF in the OC, and mobile 1 5w30 in the lower legs. The fork in trail mode has a lot less compression dampening than before, which is what I was after. There's a lot less stiction overall too! I was blowing through travel with this setup, so I added 5ml of oil into the air chamber. Feels pretty decent, much better than the stock setup, but I need to get more time in the saddle. BTW, mine must be a later model fork, as it has the 4 holes drilled, and has a white plastic piece with 4 small check valves to keep cartridge fluid from leaking out. The fork is a factory spec off of a '13 Pivot Mach 5.7 that I bought (lightly) used.

  21. #21
    rgf
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    Quote Originally Posted by rgf View Post
    Thinking about selling it when it gets back from service.
    Hey guys, the fork (originally a float 32 evolution 150) came back from service with a new steerer and a FIT CTD with Trail Adjust cartridge. Now I'm not sure if I want to sell it anymore...

    I was looking at a 2014 Marzocchi 55 CR but reading the DBC cartridge description it sounds awfully similar to the O/C one. Hybrid between open bath and sealed cartridge, oil is dumped in the lowers in case of high pressure and sucked back in later... Do you guys have any insight about it? Would I be getting just a stiffer fork with a worse damper?

    Thanks and sorry for the OT!

  22. #22
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    Why not give it a try? I demoed a Yeti SB5 last weekend with a Fox 34 CTD FIT fork, and really liked it. Sweet bike too!

    Update on my Evo fork; in addition to the Mobile 1 fluids, I replaced the Fox Float fluid in the air chamber with Redline heavy shock proof gear oil. This stuff is so slippery that it is not recommended for synchronized gear boxes. I added an additional 10 cc to the chamber to get a little more support from mid stroke on. The fork rides so much better! Small bump compliance is excellent, and I'm not blowing through travel like I was before. If you don't mind tinkering, you can get these forks to work pretty well.

  23. #23
    moaaar shimz
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    10cc is a lot, you'll see in your next service that the oil has migrated into the lowers.

  24. #24
    rgf
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    Quote Originally Posted by daytonadogie View Post
    Why not give it a try? I demoed a Yeti SB5 last weekend with a Fox 34 CTD FIT fork, and really liked it.
    I am, still not sure of the outcome though. Fit damper seems to work fine, you can appreciate both compression and rebound clicks effects on the ride.
    It just feels a lot sticky, especially on small bumps, I doubt it's from the damper, probably it's just dry or too much float fluid in the air chamber or both. Wouldn't be the first time I see a fork come back dry from Fox service...

    Could even be that they changed the bushings and needs to wear them a bit... too bad I have no way to know it since they don't give any report about what they actually did on the fork, I have to figure it out looking at it.

  25. #25
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    Hello, does have FLOAT EVOLUTION some air volume spacer under air volume cap? Something like this: http://fcdn.mtbr.com/attachments/sho...ke-air-cap.jpg

    It is too progressive for me even if I pump low pressure (SAG 25%)

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