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RS Rev dual air not fully extending.

jairajjairaj Posts: 3,009
edited March 2013 in MTB workshop & tech
I recently performed a lower leg service on my forks as they where very stiff and had lost all small bump compliance. Afterwards the forks felt fine and where back to normal.

After a couple rides the seal on the air spring side popped up mid ride. I did some trail side repairs. pushed the seal back on and added some air to re-pressurise the fork. I rode back home gingerly but the fork felt okish.

On my return home I noticed that the fork has reduced its maximum travel by 5mm. I emptied all the air out of both +ve and -ve chambers. Pumped up the +ve to 110psi and the fork returned to its maximum 150mm but when I added 110psi to the -ve chamber the fork was pulled down into its travel by 5mm.

A quick bounce on the fork inside my home and everything feels ok but the fork won't extend that last 5mm.

Any ideas what's gone wrong or what I should check?
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Posts

  • supersonicsupersonic Posts: 82,708 Lives Here
    This is normal for a Dual Air fork, the more negative air you add, the more it pulls the fork in. Try 105psi in the negative.
  • jairajjairaj Posts: 3,009
    But my normal settings are 110psi in positive and 120psi in negative to give me a more supple feeling. I have never experienced the fork being sucked into its travel when the positive and negative are roughly the same. Sure when the negative is 20psi more it will start to pull the fork in but not at 10psi more?

    The fork does not extend back to 150mm even when the front wheel is lifted up and un-weighted. If pulling into the travel is normal then how do I get the full 150mm of travel? surely the most I will get is 145mm?
  • jairajjairaj Posts: 3,009
    Also is the sealing popping out a symptom of some other problem? or could it just be that I did't push the seal in far enough when I replaced it?

    thanks for the help.
  • PlyphonPlyphon Posts: 433
    This happened to me last week, however my forks are sucking in about 15/20mm at my normal 10psi more in the negative chamber.

    (my left fork seal popped out also.)

    I've not really been able to get a conclusive answer but some people said air might of gotten into the lowers, creating pressure and popping off the seal.

    Some people say this isn't possible, no one really knows.

    All I know is that my seal popped, the forks lost some air in both chambers, and when I repressurised the forks felt horrible and sucked in when I put my regular pressures in.

    I'm going to service the lowers and service the air spring (replace all O rings basically) as I think a ring somewhere has gone, I'm taking it on this weekend.

    I will let you know my results!

    Oh and yeah prior to this my fork didn't suck in at all with +10 psi in the neg.
  • jairajjairaj Posts: 3,009
    thanks I'll be interested to see what you find.
  • DCR00DCR00 Posts: 2,160
    you could have trapped air in the lowers when you put the forks back together. Same happened to me. I did a test cycle after putting them back together and the right hand seal popped off. Was fine after that.
  • jairajjairaj Posts: 3,009
    Thing was the forks were fine for a couple rides with full extension behaving fine etc.. It happened mid ride. Does this mean an air seal has given way and leaked air into the lowers ?
  • clamps81clamps81 Posts: 315
    This happened to me as well. Periodically my fork would decide that it wanted to be 130mm instead of 150m.. Air seals presumably. Emptying out both chambers, resetting the travel and then filling them again sorted it, but II got fed up with doing that and just had it converted to coil, which suits me far better.
    Nukeproof Mega AM


    Tomac Snyper - Now sadly in pieces
  • supersonicsupersonic Posts: 82,708 Lives Here
    Here's the deal - RS forks stated travel is +/- 3mm when the chambers are exactly equal pressure. Sometimes can be hard to get them the same as the -ve chamber is small. As soon as you go above the +ve pressure it will suck down into the travel slightly.

    But the forks can leak air into the leg structure, which causes problems. An air spring service kit is the way forward ie replacing all of the o rings.
  • jairajjairaj Posts: 3,009
    ah I didn't know that. So chances are they are probably fine then.

    I'll give the forks another ride on the weekend if they feel fine then I'll stick with it.

    If they feel different in any way I'll get a full service performed too.

    thanks for the info
  • PlyphonPlyphon Posts: 433
    So.

    I performed my air spring service and lower service.

    Some strange developments!

    Before the service my pressures were 35+ and 45-. (I'm very light.)
    Now, I have to have 80 psi to get the same sag.

    If I have the negative 10 psi more than positive, it sucks it like 20/30mm. (I can pull it out by hand but it sucks back in)

    If I have the negative the same as positive, it sucks it about 1cm. Or rather, doesn't extend the last 10mm.

    Any ideas why this is? Should I just carry on reducing the negative until it doesn't pull in?

    Other than that the fork does feel fantastic thanks to the new oil etc.
  • supersonicsupersonic Posts: 82,708 Lives Here
    I'd try reducing the negative as is hard to get the exact figure you want. if the fork still feels supple then all is good.
  • PlyphonPlyphon Posts: 433
    So,

    Just to humor myself I tried again making sure I follow the correct method to set the chambers:

    1) let out negative air
    2) set positive air
    3) set negative air to same values as positive air
    4) check seated sag
    5) if sag is incorrect return to step one. NOT step 2!

    The fork sucks in with both chambers at 80psi. If I let out negative, the fork jolts back to full travel. I measured, and it's sucking in 20mm.

    The fork starts to suck in at around 50psi in the negative, with 80 in the positive. I set the chambers again and put 50psi in the negative and it sucks in about 5mm, which I could live with, but obviously something isn't right.

    My questions are -
    1: Why before my service was 35psi +ive, 45psi -ive giving me correct sag if those pressures are so low? Do you think friction from lack of oil & lube? The fork performed brilliantly at those pressure.

    2: Why now when I set the chambers using the correct method does the fork suck in 20mm when both chambers are the same psi?

    We will get there eventually...
  • supersonicsupersonic Posts: 82,708 Lives Here
    Could be friction or a damper problem for Q1.

    Seated sag is another reason why the figures are low - it should be set standing.

    What is the shock pump? Some are very off at measuring lower pressures.
  • PlyphonPlyphon Posts: 433
    yeah sorry I do set sag standing in the attack position not sat down, that was a typo.

    I've no idea what it is... think it probably is a cheapo !
  • PlyphonPlyphon Posts: 433
    It has occurred to me that my pump might be under-reading the true value.

    Unfortunately I don't have access to another to check.

    If I just add air until the first signs of pulling down (say I get it so it pulls down 3 - 10mm) - and rode the fork like that, would it cause any damages?
  • supersonicsupersonic Posts: 82,708 Lives Here
    Not at all. What feels best is best.
  • PlyphonPlyphon Posts: 433
    I'm glad you've said that -

    I just this minute pumped the positive to 80 and the negative to 50 (whereby it starts to pull down, approx 3mm - which I can live with!)

    The fork feels great at these pressures, super plush, not too much bob or dive, and good small bump.
  • supersonicsupersonic Posts: 82,708 Lives Here
    All sounds good to me!
  • My dual air rev did exactly the same and it was bloody annoying so I feel your pain!

    Although, I have a single air Reba now and would much prefer the dual air. The black box dual air rev was THE best fork I've ever used... set up exactly how I wanted and so so so supple.

    Took me bloody ages to get it "just so" however.
  • supersonicsupersonic Posts: 82,708 Lives Here
    Black Box Reba Ti dual air best fork I have had too. Be a long time until they match these.
  • jairajjairaj Posts: 3,009
    I've been thinking of upgrading the damper in my Rev. I have a basic motion control unit from 2010. Would I be better off going for a Black Box Ti damper or the RCT3 damper.

    I like tuning options so I can get the fork to behave how I want it. But once I've found my setting I leave it there I don't tend to fiddle with lock out etc on climbs or descent
  • supersonicsupersonic Posts: 82,708 Lives Here
    Black Box Ti and RCT3 get a separate (but fixed) high speed circuit which helps with harder hits. However with RCT3 you lose the fine tuning of the blow off (floodgate). Both use the dual flow rebound circuit, which again helps with the big stuff. However you'd need to replace the both dampers. Not cheap.
  • jairajjairaj Posts: 3,009
    yep not cheap was hoping to sell old fork and buy a new one with RCT3 but can't find any dual air with 20mm axle forks any more. every one has the new solo air spring with 15mm axle.

    I want to keep my current chassis and upgrade the internals instead.
  • DCR00DCR00 Posts: 2,160
    supersonic wrote:
    Black Box Ti and RCT3 get a separate (but fixed) high speed circuit which helps with harder hits. However with RCT3 you lose the fine tuning of the blow off (floodgate). Both use the dual flow rebound circuit, which again helps with the big stuff. However you'd need to replace the both dampers. Not cheap.

    I did this on my Sektors.

    The RCT damper is really overpriced IMO. You can get the RLT damper for about £70, which has floodgate adjust. For me the rebound damper made the biggest difference to performance, and at £60, it wasnt too crazy price wise (that was from Loco). £130 for both isnt too bad when you compare it to the price of a new fork...
  • warpcowwarpcow Posts: 1,448
    DCR00 wrote:
    supersonic wrote:
    Black Box Ti and RCT3 get a separate (but fixed) high speed circuit which helps with harder hits. However with RCT3 you lose the fine tuning of the blow off (floodgate). Both use the dual flow rebound circuit, which again helps with the big stuff. However you'd need to replace the both dampers. Not cheap.

    I did this on my Sektors.

    The RCT damper is really overpriced IMO. You can get the RLT damper for about £70, which has floodgate adjust. For me the rebound damper made the biggest difference to performance, and at £60, it wasnt too crazy price wise (that was from Loco). £130 for both isnt too bad when you compare it to the price of a new fork...

    Did the same here: BB rebound and RLT comp. damper in one of the cheap 20mm Maxle sektors from Merlin. The RLT is all I've ever found I needed on RS forks, just to set a bit of low-speed damping. Also found the rebound damper gave the most noticable change though. Comp. damper cost me about £50 through my LBS and the rebound was £60. If I could only do one it would definitely be the rebound.
  • cameraukcamerauk Posts: 1,000
    I am just in the process of doing this to my Reba dual air forks from my Camber Expert
    I phoned TFtuned and the chap said all I needed to replace was just the Motion Control unit which I have ordered (RTL3), I asked about the rebound damper and he said unless I put the Blackbox one in it would make no difference.
    The Fork is Reba TK which only had a very basic lockout unit in it
    Specialized Camber Expert
    Specialized Allez Sport
  • DCR00DCR00 Posts: 2,160
    camerauk wrote:
    I am just in the process of doing this to my Reba dual air forks from my Camber Expert
    I phoned TFtuned and the chap said all I needed to replace was just the Motion Control unit which I have ordered (RTL3), I asked about the rebound damper and he said unless I put the Blackbox one in it would make no difference.
    The Fork is Reba TK which only had a very basic lockout unit in it

    I dont think there is a Blackbox specific rebound damper. All ive seen is the dual flow, which you get on the likes of the Rev, and the Mission Control damper, for the bigger forks. Ive had similar advice from RS, but they suggested that there was little point changing the comp damper if i wasnt going to change the rebound damper...
  • cameraukcamerauk Posts: 1,000
    Well that was a no starter I have received the new damper unit but it won't fit in the top of the leg
    Will have to get on to TFtuned in the morning and find out what has gone wrong either it is wrongly packaged or they have ordered the wrong unit :(
    The unit they have sent is part number 11.4015.544.050
    Anyone with any help on this
    Specialized Camber Expert
    Specialized Allez Sport
  • supersonicsupersonic Posts: 82,708 Lives Here
    Looks like you have bought the damper for a 120mm SID.
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