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  1. #1
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    Inside the Fox RC2 Damper

    I noted in my own teardowns following the Fox site that they leave out some steps, along with conspicuously leaving out what the actual damper in the RC2 cartridge looks like.

    My 36 has been in service for nearly a year, and a trip to the local bikepark revealed that without any doubt, my bottom out was too hard for me. I can't really get travel past where the mechanism noticeably and audibly takes over without sagging so far that I'm too low. So my goals were to reduce bottom out resistance, along with changing the oil because the cart was feeling a bit sticky (since everything else was lubed). The additional goal was to see what the RC2's valving assembly looked like, especially for the purpose of modifications. Additionally, a small volume of oil may have bypassed into the bladder over time, leading to a minor harsh top out. Enough to feel it. Indeed, there were some drops of oil in there and the cart was not smooth.

    There will be little dialog accompanying the pictures and I decided to not turn this into a DIY tutorial for the time being.

    Unscrew the top cap (so one may pull the cart out completely after the foot nut is removed and the bottom is tapped out.)



    The damper in one piece:


    Where the bottom out piston is set to activate. Was basically losing this much travel due to it.


    Remove bottom damper cap nut and use a combination of forcing the damper rod in a but, along with twisting and pulling of the cap to remove the bladder.




    The bladder (clean inside and out, grease all edges):


    The damper and the bottom out portion removed from the main housing. The damper itself is inside the silver housing, while the portion that protrudes is where the bottom out assembly plunges into. Note the holes.


    The bottom out control. The Fox explanation is worded a bit poorly. The seal at the end of the shaft plunges into the female portion and seals restricts flow, or rather flows oil through a greater restriction. The lower it is to the bottom of the shaft, the earlier you hit bottom out, which I find to be a bit too abrupt so early because I'm not really hucking yet. One has to remove the 2mm bolt at the end and pull up the "glide ring" and spacers and move it back. I ended up moving mine up (away from the end) to all but one small spacer. So far, so good, and perhaps I can dial HSC to help with the bottoming also, though in this design it was made to be distinct from BO.



    With BO reduced, for example (My final position was still higher). One can screw the assemblies back together and then cycle the damper shaft to see where the engagement point is. I went off this to determine a yet higher BO point (bottom out is closer to bottom in travel).


    All the main parts of the damper and pretty much where the Fox manual leaves off:



    The damper disassembled. Pink rubber gloves for grip to remove the caps and screw then back together. Had to use a hair dryer due to possible loctiting on the threads. Not shown is a spring inside the cap that holds the single shim down, I guess simulating reinforcing shims in a stack, since this design doesn't hold it down with a center bolt.







    Last edited by Jerk_Chicken; 09-17-2008 at 02:05 AM.

  2. #2
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    Excellent post!
    Had to fix my R cartridge myself as the local rep did not have the part in stock.
    Thanks
    A different angle on bikes:
    www.ofanaim.net/has.html

  3. #3
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    Nice post. I'm interested to hear your riding impressions. I have done multiple damper oil changes on my '06 but never needed to change the BO since it was already at firmest. My '09 has a noticeably stronger BO and I may need to change it...especially on my wife's. I see no need to change the overall damping however since it's pretty well dialled in stock form for me.

  4. #4
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    I just came back from a ride today. My guesstimate of the BO piston position (with only one small spacer between it and the main piston) was perfect. I get full travel and no harsh bottoming against the crown. This gives me about 7-8mm or so of bottom out ramp. So now that missing 20mm or so is tacked onto travel. Changing the damper oil really helped things out. The whole thing feels smoother and has way more small bump sensitivity.

    Unfortunately, I don't huck, so that BO position was essentially useless and reduced my travel.

  5. #5
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    I agree that the damper oil change makes a huge difference on these forks. I went 2 seasons on stock oil before changing mine and quickly regretted waiting that long. What weight of oil did you go with?

    I don't think I would drop the BO quite as much as you did...maybe 1/2 way to gain 10mm or so but keep a little safety margin for those botched landings. I don't exactly huck this bike but I do a lot of small drops with root infested landings that can be harsh if you get unlucky at high speed.

    I did have a strange occurance with my '06 van a couple weeks ago. I nosed into a roller really hard and bottomed it. After that I had a terrible knocking on rebound and a dead spot with no rebound damping for about 1cm of travel. I think the impact forced a good amount of oil out of the damper past the bladder. I changed the oil and all is well now. Since this had never happened in the past I'm wondering if the bladder has gotten a little hard and doesn't seal quite as well anymore.

    I actually picked up a second '09 Talas last night because my wife refused to give mine back after I "loaned" it to her to try out. Again I dropped the oil as soon as it came out of the box and this one was even lower. I would guess about 5cc was in each leg. It would have likely been dry in less than a week of riding. I feel sorry for anyone that doesn't check it before riding it.

  6. #6
    Nightriding rules SuperModerator
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    great post, JC!

    now that's a real tear down

  7. #7
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    Spectro 85/150 Based on the CSt, it should be close (16.90 vs 16.10 of Torco RFF7), but about half of RSF.

  8. #8
    Underweight Rider
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    erm...whats that in oil weight terms? 7.5W? 5W? bcoz i'm longing to tear down my month old 09 Van36 RC2.....>.<

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    nice detail.

    did you turn the two comp dials to see what effects what?

    I am guessing the low speed controls an orifice size the the high adds tension to the spring?

    I think the oil you used may also me lighter weight then spec. Fox says 10wt for RC2 but if I remember right their 10wt is thicker than Torco 10wt but its been like 6 months since I did one and looked. I only did a straight oil change and bleed (didn't have enough time to completely take apart the damper and check for myself how they due there low and high comp). The BO is pretty straight forward just like the sleeve for the 888 you could add.

    and yes frequent oil changes are not a bad idea for RC2 esp the 40 since it runs alot of travel and very little volume, dh all day so heat gets fairly high.

  10. #10
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    It is lighter going by the wt, but it has not produced a massively different ride. However, it does feel like it works better on my terrain and so far I'm running everything nearly wide open.

  11. #11
    Underweight Rider
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    Would it be safe to run 5wt instead of 7.5wt?

  12. #12
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    It's not all about the weight. You have to check out Pete Verdone's analysis chart to see how the ratings are all over the place:

    http://www.peterverdonedesigns.com/lowspeed.htm

    DO NOT GO BY LABLED OIL WEIGHT! Not only is this a poor way to decide which oil to use, but each manufacturer seems to be on a different scale. For example Maxima RSF 7wt is actually lighter than Spectro 5wt and Silkolene Pro RSF 7.5wt is actually heavier than Showa SS-8 10wt. This is not a judgment about the quality of these oils, just that the 'weight' label leads to a lot of trouble when trying to tune with suspension oils.

    Suspension oil is labeled by weight because consumers are used to thinking of oil (ie. motor oil & gear oil) in these terms. The SAE weight system has a very broad and vague viscosity range and does not even cover the viscosity range that most quality motorcycle suspension systems require. Another point of confusion is that motor oils and gear oils are rated for viscosity on the SAE scale at different temperatures, leading to similar viscosity oils having very different ratings. SAE J300 is used to define engine oils, while SAE J306 is used to define drive line (gear) and chassis lubricants.

  13. #13
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    hey JC did you play with the comp dials with it apart to see what did what?

  14. #14
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    Quote Originally Posted by Jesse Hill
    nice detail.

    did you turn the two comp dials to see what effects what?

    I am guessing the low speed controls an orifice size the the high adds tension to the spring?
    +1 on the nice write up and

    +1 on wanting to know how the level of sophistication of external damping tuning.

    P

  15. #15
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    Ah i see, thanks JC for the insight

  16. #16
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    Just an FYI - I opened up my '09 talas 36 last night to drop the bottom out setting and it's not there anymore. I have done this on my old '06 van and it helped quite a bit. On the '09cart the assembly ends right after the pink glide ring...no more spacers and black guide ring to adjust. Not sure if there is another method to change the bottom out or not. I hope so since I'm not setting the last 1 1/2 inch of travel. I did go to slightly heavier cart oil in the hopes of being able to run less air pressure without getting too divy and use the travel more effectively.

  17. #17
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    Here´s my speculation.
    Last year (eeeer 2008 and 2007) the Float forks had a damping cartridge without the hydraulic bottom out unit. They were progressive enough without it.
    The Talas was not that linear too (in my oppinion)
    Also the 2009 Talas has less air chambers, probably is a bit closer to a Float (spring curve progressive etc. less stiction)

    Maybe they got rid of it, as the spring curve provided enough ramp up?

    Now maybe only the Van has that internal hydraulic bottom out, as the coil spring is really linear?

    Greetings Znarf

  18. #18
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    I just took a look on the fox service site and they do have a different fit service write-up for the float and the assembly is identical to my '09 Talas one. Looks like you're right znarf.

    Wierd thing is that in the TALAS3 service write-up they link to the standard fit service document that shows the bottom out assembly.

  19. #19
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    Yeah,
    probably a website mistake.

    If you look closely at last years service instructions, especially the pictures of the Float/Talas with our without the bottom out shaft, you can see, that they just took the same picture and removed the bottom out thing with Photoshop or whatever

    (and I definitely spent too much time on that site, noticing details )

    Greetings Znarf

  20. #20
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    And within the float service procedure you can actually see the bottom out assembly in one step but not the rest. They should fire their photoshop guy...

  21. #21
    MC MasterShake
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    Quote Originally Posted by Znarf
    Here´s my speculation.
    Last year (eeeer 2008 and 2007) the Float forks had a damping cartridge without the hydraulic bottom out unit. They were progressive enough without it.
    The Talas was not that linear too (in my oppinion)
    Also the 2009 Talas has less air chambers, probably is a bit closer to a Float (spring curve progressive etc. less stiction)

    Maybe they got rid of it, as the spring curve provided enough ramp up?

    Now maybe only the Van has that internal hydraulic bottom out, as the coil spring is really linear?

    Greetings Znarf
    You are correct. I opened up my 08 Float 36 looking for the BO spacers and they were not there. I called Fox and they told me the Floats were progressive enough that they didn't require a BO control. I asked him how I could get back that last inch of travel and he told me to run less pressure and more HSC and LSC in the fork. I tried that but it didn't seem to work. The fork ended up riding really deep in it's travel and I still end up missing about 3/4" of my travel. I'm going to have to play with this some more. Besides that issue this fork is really plush. Moreso than my 07 Vanilla.

  22. #22
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    after one of JC's threads i changed the oil in my 07 TALAs and i had to re adjust the talas timing, now its works like it was in the factory. perfect.

    thanks for putting the time into the photo's.

    G

  23. #23
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    So which model year are supposed to have a BO control like seen above? I'd love to open my fork as it has the exact same problem, I can't use the last inch of travel, no matter what I do with the adjusters.

  24. #24
    MC MasterShake
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    Quote Originally Posted by Radical_53
    So which model year are supposed to have a BO control like seen above? I'd love to open my fork as it has the exact same problem, I can't use the last inch of travel, no matter what I do with the adjusters.
    I would assume the Van and Tal models would have them but I wouldn't count on it. You'll have to check with Fox.

    I think your best bet is to check your fluid levels first My 08 Float wouldn't use that last inch of travel despite multiple drops in the 7 to 8' range. I cracked it open and of found that there is no BO adjustment on the Floats. But, when I checked the fluids my damper side leg was spot on, the air chamber has 25cc's instead of 5cc's and the leg had 5cc's instead of 25cc's. I corrected the fluids and now I get full travel. I'm actually having problems now with it bottoming too easy. I'm playing with adjusters but I made add a couple of cc's into the air chamber

  25. #25
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    As I said above, the '09 talas does not have the bo adjustment. Not sure about the '08. I believe all the vans will have it.

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