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  1. #1
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    firebird DHX issues

    Hello all. I've been lurking more than posting lately, but now I have a real problem so here goes:
    The issue I'm having with my DHX rear shock (This is a 2012 shock/frame.) is it seems to sag too deeply into the travel, creating major geo issues on moderately steep climbs. I set the bottom out pressure/volume according to the recommendations on the Pivot website. In the main air chamber I had it originally set to 210 (my ready to ride weight + 5 - 10 lbs.)
    After I started noticing these handling issues on recent climbs (there's also a fair amount of shock movement when I'm just pedalling along, this is what alerted me that something may be going on with the rear shock)
    So I decided to reset the air pressure/sag. When I put on the shock pump I was surprised to notice that there was still about 200 psi in there even though I appear to have about 55 - 60% sag.

    So I pumped it up to 230 psi and 'sat down hard' to check the sag. It was down to about 50% now. The weird thing was if I checked the sag just by sitting down on the bike , it lined up with the red hash mark, so what gives ? If I do it the Pivot way, I'm way over in sag
    , and this is probably why I'm getting a bit of squat or pedal bob now. Any ideas what I need to do to get decent performance out of this shock ?
    Last edited by le_buzz; 09-10-2012 at 07:21 PM.

  2. #2
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    Hmm, I'm not really sure what's going on here but the 1st thing I'd do is vent off all the air and see if the shock stays up or if it pulls down. There is a possibility that an internal seal could be leaking and pressurizing the wrong side of the piston. I haven't heard of this problem since the 1st year that the shock was available but it's possible you have a bad seal. The other thing would be to recheck your sag without referencing the pressure gauge, just go by the actual sag measurement. I've seen PLENTY of faulty pressure gauges so I don't really rely them for much more than a reference. Try those things and let me know what you get. Remember to sit down HARD on the saddle before resetting the O-Ring and measuring sag. Just doing that part wrong can give a false reading...
    Desert Sunset Calls/Upward, Pain, Perseverance/Welcome Solitude

  3. #3
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    Quote Originally Posted by kenbentit View Post
    Hmm, I'm not really sure what's going on here but the 1st thing I'd do is vent off all the air and see if the shock stays up or if it pulls down. There is a possibility that an internal seal could be leaking and pressurizing the wrong side of the piston. I haven't heard of this problem since the 1st year that the shock was available but it's possible you have a bad seal. The other thing would be to recheck your sag without referencing the pressure gauge, just go by the actual sag measurement. I've seen PLENTY of faulty pressure gauges so I don't really rely them for much more than a reference. Try those things and let me know what you get. Remember to sit down HARD on the saddle before resetting the O-Ring and measuring sag. Just doing that part wrong can give a false reading...
    Thanks for the tips. After venting off all the air the shock does stay up, so its probably not a seal if thats what happens when you have a faulty seal.

    I also reckecked the sag by putting the O-ring and sitting down hard. Still the same result of about 50 - 55% sag. When I first screwed on the nozzle on the shock pump, it read 220 psi in the gage, and I had to 230 the day before, so if the gauge is working correctly Im only losing 10 psi when I unscrew the nozzle. As I'm right around 200# ready
    to ride, this seems like (220 - 230) a reasonable setting. I also tried monkeying with the bottom out volume on my last ride, but it just made the ride more harsh, so I put it back to the original recommended turns. The shock is set up correctly as far as I know, this is perplexing.

  4. #4
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    PSI don't mean **** if you aren't sagged right. Whatever your preconceptions of what air pressure you "should" be running here are off. There is no reason to think you should be running body weight (or some approximation thereof) to get the right sag, unless that is what you are seeing on THIS frame with THIS shock from other riders on the forum. Even if the Pivot site says something about setup here, are you sure you aren't mixing up the resivoir PSI with the shock body PSI? I assume you have a DHX Air...

    Is this the guidance you are citing from Pivot?:
    Setting Rebound, Bottom Out, and Boost Valve on DHX Air Shocks: In general, a good starting rebound setting is 7 clicks in from fu
    open for a rider weight of 170lbs. We recommend setting the bottom-out with two lines showing on the reservoir. A good starting Boost
    Valve pressure is 170psi. We do not recommend going below 150psi on the Firebird.


    They are referring to boost valve pressure, not spring/cannister pressure.


    Set your sag to 30%ish, regardless of what the pump says. Then go ride.

    Also, you aren't losing pressure from the system when you disconnect the valve, you are losing it when you re-connect. You are adding volume to the system (as the pump isn't pressurized) and that pressure is now dispersed over more area.
    Last edited by CharacterZero; 09-12-2012 at 07:00 PM.

  5. #5
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    DHX Air: the continuing saga

    I forgot to mention that after letting all the air out,
    I pumped it back up to 255 psi. (I was planning on trying for 270, but i found that after 255 I just couldn't
    get any more air in there without possibly risking damage from overinflation - I would either have broken the pump or perhaps a seal ini the shock ?)

    After that I decided, just for shyttes and grins, to check the boost valve air pressure, and lo and behold - there was none. The reservoir was basically empty. Now, this was the first time i have checked this since I initially setting it up back in Jan., so my first question is, is this normal for the boost chamber to lose all of it's air over 6 mo. of use ?

    I've had the DHX Air on a couple of other bikes and don't remember having this kind of issue with those. So I pumped the boost chamber up to 190 psi (wanted to err on the side of a bit too much pressure this time, rather than too little.)

    I went on a ride yesterday on which there were occasions to test this new setup on chundery stuff with lots of sand and square edged boulders washed down from the recent rains as well as loose, technical climbs and descents that were mostly short but steep (Tucson Mountain Park for
    anyone interested in the exact location)

    If I were on any other kind of bike, I would probably have been satisfied, but I expect more from the Firebird/dw-link than I got.

    There was some hrshness on fast, repetitive square edged hits as well as a peculiar feeling of being on a hammock where you initially absorb the impact and compress down into but then bounce back up so much that it nearly throws you off balance. It reminded me a little bit of my old
    blurXC. I had the rebound set perfectly before.

    This would typically happen when there's a slight dip in the trail between 2 close together hits.
    Last edited by le_buzz; 09-15-2012 at 05:16 PM.

  6. #6
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    I've never had my Boost chamber loose all it's air but it wouldn't take much of a leak for that to happen due to the relatively low size of the chamber. I like to check mine every few months just to be sure it's where I want it, especially if I notice the bike starting to ride a bit different. I'd recheck the sag now that you have the Boost pressure setup and see how the bike performs then. It sounds like there is still some adjusting that needs to be made.
    Desert Sunset Calls/Upward, Pain, Perseverance/Welcome Solitude

  7. #7
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    Ok so to pump the boost valve, just connect the pump, pump to the requires psi and dis connect? I initially pumped abt 200psi just to get the pump to read 170 on the next reconnection. Ouhhh shitzz

  8. #8
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    That is normal.
    The chamber has such a small volume, the amount of air that goes into the hose on reconnect drastically changes the internal pressure. Mine ALWAYS reads 150lbs in the chamber on a reconnect regardless of what I put in it.
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