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  1. #1
    g3h6o3
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    RS Reba Team Dual Air : The dreaded positive oil leak!

    Hello, this thread is the pursuit of a leak I'm experiencing with my 08 RockShox Reba and that has been going on for over a year. The process has started in the o-ring thread but given the o-ring sizes can be safely ruled out, I thought of starting a new thread.

    The problem is that I lose all oil from the positive chamber during a ride of more or less an hour. It leaks to the negative chamber and if I keep on riding the fork when it lost all it's oil, I pressures in both chambers will equalize.

    So, up to now, the fork has received a new CSU since there seemed to have some minor scratches inside the stanchion. Since this didn't help, a brand new dual air piston assembly was installed without curing the problem. There is not much left to investigate but I'm also close to giving up so if you have any idea of what I could try then let me know!

    Thanks
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  2. #2
    g3h6o3
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    Since there aren't many place the oil can leak from, I just worked on one of them. I removed the valve stem with a 9mm socket and replaced the o-ring at it's base with a 4mm x 2mm (close enough to the original).

    I might go for a 2nd ride today to test this...
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  3. #3
    nocturnal oblivion
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    It's not the top cap if its leaking to the neg. Try thicker oil on top the positive piston. Could be caused be those scratches of course, which you could test by seeing if it leaks to the neg. just while sitting with the positive at 100psi and the negative empty. If it doesn't leak then, it's the scratches.
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  4. #4
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    Same problem on an '09... No air loss, but oil always moved to the negative chamber as evidenced by it squirting out whenever checking the neg air pressure.

    Recently bought an '11 RLT for another bike, and when taking out the 20mm spacer, low and behold, there was NO oil in the air spring chamber at all. Just a blob of grease on the top of the positive piston, with all seals well greased. Referring to the the Reba 2011 Tech Manual, page 7, turns out they no longer spec oil for the air piston -- grease only.

    I guess that solved a nagging problem for them . I then disassembled my '09 fork, and set it up the same way. Problem solved.

  5. #5
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    What weight oil are you using?

  6. #6
    g3h6o3
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    Quote Originally Posted by stumblemumble View Post
    It's not the top cap if its leaking to the neg. Try thicker oil on top the positive piston. Could be caused be those scratches of course, which you could test by seeing if it leaks to the neg. just while sitting with the positive at 100psi and the negative empty. If it doesn't leak then, it's the scratches.
    There are no scratches, I replaced the whole CSU.
    I did try 80W gear oil without success.
    I can only assume it's leaking in the neg. Ther doesn'T seem to be a leak in the Shrader valve and when I disassemble the fork there is always oil in the neg. With that said, there is always oil everywhere when disassembling a fork so it could be an false impression.

    Quote Originally Posted by bad mechanic View Post
    What weight oil are you using?
    Spectro 15W in the + chamber.
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  7. #7
    g3h6o3
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    I rode the fork tonight but it wasn't a big or intense ride as it was the 2nd of the (12:15 to 1:30 & 5:15 to 6:15) day and I wasn't too energetic. I did push it hard at times but it wasn't as harsh as usual. To top it off, my rear brake had a layer of dirt "cooked" on the pads so they didn't brake well and it wasn't helping my confidence.

    I will try to give it another go tomorrow.
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  8. #8
    g3h6o3
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    Quote Originally Posted by dh_swing View Post
    Same problem on an '09... No air loss, but oil always moved to the negative chamber as evidenced by it squirting out whenever checking the neg air pressure.

    Recently bought an '11 RLT for another bike, and when taking out the 20mm spacer, low and behold, there was NO oil in the air spring chamber at all. Just a blob of grease on the top of the positive piston, with all seals well greased. Referring to the the Reba 2011 Tech Manual, page 7, turns out they no longer spec oil for the air piston -- grease only.

    I guess that solved a nagging problem for them . I then disassembled my '09 fork, and set it up the same way. Problem solved.
    Interesting...
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  9. #9
    nocturnal oblivion
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    Quote Originally Posted by PissedOffCil View Post
    I can only assume it's leaking in the neg. Ther doesn'T seem to be a leak in the Shrader valve and when I disassemble the fork there is always oil in the neg. With that said, there is always oil everywhere when disassembling a fork so it could be an false impression.
    Again for effect:
    An example if you run 100psi positive and 70psi negative and both chambers end up at 80psi, then it's the positive piston o-ring.
    The positive piston is a one piece white dome cap with an o-ring around the edge, there's nowhere else the air could get down to the negative chamber from.
    If the above is happening it's not the schrader or top cap.
    Like I mentioned, try putting 120psi or so in the positive and put no pressure in the negative. After a day of sitting if the negative has pressure when you thumbnail the negative schrader, you know it's the positive piston o-ring. If the negative doesn't have pressure, but the positive lost pressure, it'd be the top cap assembly (which you'd probably see oil seeping/bubbling from).
    There's only two culprits, the positive piston o-ring or the top cap o-ring or schrader.

    If you do the above experiment and no air is lost from the positive, your fork is either fine or it only loses positive air to the negative when the fork is cycled. The latter would indicate an inner stanchion scratch causing air to pass the o-ring when the piston passes over it, which seeing how you replaced the stanchions shouldn't be the issue.
    Good luck!
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  10. #10
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    I wasn't impressed by the durability of my Rockshox Pike's Dual AIr. I went to a Dual Air U-turn in my 2010 Reba - no air loss issues but I had a nasty top out clunk. RS waranted the assembly but I have not had a chance to install. The U-turn Dual Air is an enclosed cartridge isolated from the stanchions.

  11. #11
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    The problem is grease simply isn't the best lubricant to use there. Oil stays on top of the o-ring, while the grease will eventually be pushed away. The problem is Rock Shox is trying to use one o-ring to seal two chambers. It's cheaper, lighter, with less stiction, but it doesn't doesn't work all the well unless you have a tight fit. What Rock Shox really needs to do is go to either a quad-ring, or go with two separate (hopefully lip) seals. While I like what they're doing, RS makes are seriously head scratching engineering decisions.

    Try and heavy weight synthetic gear oil in the air chamber instead of the 15w. The gear oil will lubricate just as well, but the higher viscosity should help keep it from leaking past the o-ring.

  12. #12
    g3h6o3
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    Quote Originally Posted by bad mechanic View Post
    Try and heavy weight synthetic gear oil in the air chamber instead of the 15w. The gear oil will lubricate just as well, but the higher viscosity should help keep it from leaking past the o-ring.
    As mentionned 80W gear oil did not help.
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  13. #13
    g3h6o3
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    Quote Originally Posted by stumblemumble View Post
    Again for effect:
    An example if you run 100psi positive and 70psi negative and both chambers end up at 80psi, then it's the positive piston o-ring.
    The positive piston is a one piece white dome cap with an o-ring around the edge, there's nowhere else the air could get down to the negative chamber from.
    If the above is happening it's not the schrader or top cap.
    Like I mentioned, try putting 120psi or so in the positive and put no pressure in the negative. After a day of sitting if the negative has pressure when you thumbnail the negative schrader, you know it's the positive piston o-ring. If the negative doesn't have pressure, but the positive lost pressure, it'd be the top cap assembly (which you'd probably see oil seeping/bubbling from).
    There's only two culprits, the positive piston o-ring or the top cap o-ring or schrader.

    If you do the above experiment and no air is lost from the positive, your fork is either fine or it only loses positive air to the negative when the fork is cycled. The latter would indicate an inner stanchion scratch causing air to pass the o-ring when the piston passes over it, which seeing how you replaced the stanchions shouldn't be the issue.
    Good luck!
    I disassembled the fork about 40-50 times while investigating this issue and fully understand how it works. I could do your overnight test with air but I can tell you oil is only lost when riding. I believe it's the same for air as I did store the bike after riding only to realize days later that I had no oil in the pos. chamber yet the pressures had remained where I left them.

    So as mentioned, I could do the test specifically but I doubt air leaks when stored and I believe it only leaks on hard impacts after all oil has spilled out. In fact, it's not uncommon to hear a hissing sound on a hard impact.
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  14. #14
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    I have successfully solved the same issue with my Dual Air fork by using some very thin grease instead of oil. Ended up mixing about 4 parts of Fox Float fluid with 2 parts of Slickoleum (aka Slick Honey). The resulting mixture is very thin, yet does not drip.

    Using the Fox Float fluid alone didn't work well: even though it is very viscous, it would still leak to the negative chamber eventually.

    It is possible that the Slickoleum alone would work fine too (it's fairly thin anyway), but I didn't try that and went with a mixture right away.

  15. #15
    g3h6o3
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    I could try mixing PrepM with the Spectro oil.

    However, if it doesn't drip, it means that it sticks to the stanchions and at one point there might be no grease left to seal the o-ring, no?
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  16. #16
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    Quote Originally Posted by shapirus View Post
    I have successfully solved the same issue with my Dual Air fork by using some very thin grease instead of oil. Ended up mixing about 4 parts of Fox Float fluid with 2 parts of Slickoleum (aka Slick Honey). The resulting mixture is very thin, yet does not drip.

    Using the Fox Float fluid alone didn't work well: even though it is very viscous, it would still leak to the negative chamber eventually.

    It is possible that the Slickoleum alone would work fine too (it's fairly thin anyway), but I didn't try that and went with a mixture right away.
    I like your solution.

  17. #17
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    Quote Originally Posted by PissedOffCil View Post
    However, if it doesn't drip, it means that it sticks to the stanchions and at one point there might be no grease left to seal the o-ring, no?
    This sounds reasonable, however, I've had absolutely no issues for the 80 hours of riding since the last fork service. It is smooth and doesn't lose air. And it is time to service it again anyway, so the piston will get re-lubed.

    Also, check the service manuals for the 2011+ RS forks: they tell to use grease rather than oil to lubricate the air piston now. So I guess it shouldn't cause any troubles.

  18. #18
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    Even if it doesn't drip, it can still flow, which is what you're looking for. You want something which is just thin enough to flow back down the wall of the stanchion.

  19. #19
    g3h6o3
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    It's worth the try.
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  20. #20
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    EDIT...

    didn't read the thread, wrote completely wrong stuff. My bad.

  21. #21
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    Quote Originally Posted by PissedOffCil View Post
    As mentionned 80W gear oil did not help.
    80W gear oil is not all that heavy. For instance Castrol VMX80 has a viscosity of 59.2 cSt at 40 degC, which is equivalent to some 15WT fork oils.

  22. #22
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    Just found out I have the same problem. Although its just air and not oil thats leaking from positive to negative. Should I grease the o-ring myself, drop some oil in the pos side, or take it to a LBS for warranted service? It was a mail order Sette Razzo, so the LBS would probably charge for labor which I assume isn't included by the RS warranty.

  23. #23
    meow, meow.
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    Quote Originally Posted by shapirus View Post
    I have successfully solved the same issue with my Dual Air fork by using some very thin grease instead of oil. Ended up mixing about 4 parts of Fox Float fluid with 2 parts of Slickoleum (aka Slick Honey). The resulting mixture is very thin, yet does not drip.

    Using the Fox Float fluid alone didn't work well: even though it is very viscous, it would still leak to the negative chamber eventually.

    It is possible that the Slickoleum alone would work fine too (it's fairly thin anyway), but I didn't try that and went with a mixture right away.
    Have you ever tried to use Rock N Roll Super Slick grease for that?

    I'm currently in the Float Fluid / full synthetic viscous oil camp, but that stuff doesn't last long in too many (RS and Manitou) forks that I encounter, so I'm trying to find out which o-ring grease is better.
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  24. #24
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    If all else fails, you can convert it to coil spring. If the inner tubes are scored, no seal in the world is is going to seal it.

    I basically got a used Reba SL 29er fork for super mega cheap (as in, cheaper than the shipping to get it to my house) on the knowledge that it probably needed a full rebuild... and even that might not bring it back. Well, new seals, and it still leaked down.

    So, I converted it to coil using a Pike U-Turn coil for $45. Add another $25 if you actually care about having a U-Turn knob on the top.

    The fork is now pretty heavy, but man, it feels pretty amazing.

    Now, the damper leaks out the top a bit. It's not show stopping. It's just some seepage, but I don't wanna spend real money on fixing it.

  25. #25
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    Quote Originally Posted by pimpbot View Post
    Now, the damper leaks out the top a bit. It's not show stopping. It's just some seepage, but I don't wanna spend real money on fixing it.
    FWIW, some RS MC dampers have such leak from new.
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  26. #26
    g3h6o3
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    Quote Originally Posted by pimpbot View Post
    So, I converted it to coil using a Pike U-Turn coil for $45. Add another $25 if you actually care about having a U-Turn knob on the top.
    Was it a 26in or 29in fork? In a certain thread, some people used the Revelation spring instead because the travel matches the Reba better (80-130mm versus 90-140mm IIRC)
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  27. #27
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    So I have a new 2012 Reba RL 29 and it seems way tooo plush. I am only 150lbs and have the air pressure at Pos 125 Neg 110-15 just to try to make the fork a little firmer to no avail. According to the fork, I should only need 100psi in both chambers. I have the rebound turned all the way up and it still does not nearly feel stiff enough for my liking. I had a ’07 tora single air before I went 29er and never had an issue once with it being to plush. Any chance some of the issues on this thread could be related to my issues, or did it come from the SRAM factory without enough oil in the POS CHAMBER or maybe the damper/motion control???? I am sort of a noob with these dual air issues. Also, when fully locked out it will still compress 2 inches which is not a good sign!!!

  28. #28
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    You may want to check the oil level in your damper.

  29. #29
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    Quote Originally Posted by bad mechanic View Post
    You may want to check the oil level in your damper.
    Do i need to remove the lower legs? and if not, do i need to release the air from both chambers and does the rebound need to be a certain position? Also is there a way to see how much oil is in the damper without actually dumping it all out or are you just sort of eyeballing it and adding more in through the top if you think its low? Thanks for you help!

  30. #30
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    Make it 125 pos/90 neg and discover what a stiff fork is

  31. #31
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    Quote Originally Posted by volume331 View Post
    Do i need to remove the lower legs? and if not, do i need to release the air from both chambers and does the rebound need to be a certain position? Also is there a way to see how much oil is in the damper without actually dumping it all out or are you just sort of eyeballing it and adding more in through the top if you think its low? Thanks for you help!
    You don't. Remove the damper side top cap. The oil should come a little over the top of the piston (located at the bottom of the spring tube).

  32. #32
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    Quote Originally Posted by bad mechanic View Post
    You don't. Remove the damper side top cap. The oil should come a little over the top of the piston (located at the bottom of the spring tube).
    I removed the damper side top cap and pulled the damper out. I guess I am a little confused on what you are referring to as the top of the piston any more details would be greatly appreciated I am not really familiar with these internal parts yet

  33. #33
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    Quote Originally Posted by shapirus View Post
    Make it 125 pos/90 neg and discover what a stiff fork is
    Deff tried that and many other pos/neg combinations, no success which leads me to believe it is a lack of oil and not an air issue, The Air seems to be holding just fine. Thanks for your suggestion tho!

  34. #34
    "El Whatever"
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    Quote Originally Posted by volume331 View Post
    I removed the damper side top cap and pulled the damper out. I guess I am a little confused on what you are referring to as the top of the piston any more details would be greatly appreciated I am not really familiar with these internal parts yet
    He means the top of the compression piston which sits ate the bottom of the spring-tube.

    Measure its length, then use a straw or any sort of dipstick to eyeball properly, so oil reaches to a point where it covers the piston located at the bottom of the spring tube.

    The spring tube is the thingy between the topcap and the compression piston (that thing with an o-ring at the bottom). Depending on the damping unit it can be a plastic tube, a red-holed plastic tube, a titanium groove-holed tube or a DNA chain looking plastic tube,.

    I assume you already bought some oil to top up. I'd just dump all oil and put the right amount for peace of mind, we're just talking 130cc's or so. It's not a car engine where you need like 4 qts of oil. You are not saving anything or making your life easier by just topping up, but that's just my opinion.
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  35. #35
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    I know this thread is ancient, but I had another idea.

    Maybe your bushings were shot and allowing enough axial misalignment under load to create temporary leaks (specifically through the 10x3mm oring in the middle of the negative piston).

    A round hole becomes an oval when you tip it a bit.

  36. #36
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    Did this ever got solved OP?

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