Monarch RT3 DebonAir - no preload, odd 'bump'- Mtbr.com
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  1. #1
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    Monarch RT3 DebonAir - no preload, odd 'bump'

    I've a 2016 Monarch RT3 with DebonAir, and the first few rides were great. I've fitted a couple of the volume spacer rings, and after refitting the can and going through setting up preload, I've found that the shock had next to no preload - I've gone up to 250 psi and I still get 30-40% sag!

    Also, there's a "bump" at about the 15% sag point - feels like the shock is rubbing past something. Here's a video with about 150 psi in the shock where I've tried to put a constant force down and you can see and hear the "bump" at about the 15% sag mark:
    https://goo.gl/photos/RGDiHYoddiAY5Cjc6

    Any ideas as to what might be causing this?

  2. #2
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    Have you let out all the air and cycled the shock to release the negative air, then re-inflated and equalized it?

    Have you removed the outer sleeve to check that the spacers (or some grease) aren't blocking the equalizing holes?

  3. #3
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    I have a Trek Slash with the same issue. I never noticed it on the trail. Only when I push down on the seat with my elbow. A squish sound the first 10mm of travel. I am 200lbs and have about 250psi to get the 30% sag.

    Sram asked if the shock sucked down in travel with no weight on the bike. I still get full rebound. Does the rebound dial work if you make rebound slower or faster? My shock came with 2 bands in it. I removed one and added one and still has the same noise.

    I may send it to Sram to have them look at it but it still works fine on the trails.

  4. #4
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    BenL, what kind of bike do you have?

  5. #5
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    To elaborate on this a little more, I have a clip of me just pushing down on the shock and one into the travel with all my weight on it.


    https://www.youtube.com/watch?v=HTm9SLVUatY

    https://www.youtube.com/watch?v=jFaTw4TgTU4

  6. #6
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    fsrxc: yes, we went through a few cycles of pressurising/equalising, and also carefully checked the seals were in the grooves properly and the debonair holes look a-ok. We removed the rings to eliminate them as a cause.

    bigb73: this is on a Merida One-Forty 7.900 (2015) (factory shock was a Fox Float CTD BV LV). It's actually my son's bike. Rebound seems ok, both slow and fast settings, other than the 'bump' or 'lip' at around 15%. Thanks for your videos; what compression setting were they at?

    We sent the shock to SRAM Australia, who just returned it with a service note that basically says "no problems found". The problem persists. Here's a series of videos showing the lack of compression on all of open/closed/pedal settings, with my 60kg (130lb) son sitting on the bike and lightly bouncing (at 150 psi).

    https://goo.gl/photos/snQLvYCoYa65ypM97

    As you can see, the shock is compressing more or less the same regardless of the open/closed/pedal setting, and nearly bottoms out with a pretty light touch. When actually ridden the shock is fully bottoming out, even at ~200-220 psi, whereas when it was first installed it was great at around 160-180 psi, and there was no feeling of the 'lip' at about 15% sag.

    Discussions w/ SRAM are continuing... I get the impression SRAM simply dismiss the issue as "user error" (which it may well be, just tell me where we're going wrong :-). I think we'll have to find a LBS who can assess the shock and provide SRAM with an independent account.

    Ta,
    Ben

  7. #7
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    Hmm. Are you sure the air volume reducer rings are in the proper part of the air can? The spacers should be towards the eyelet (top) part of the air can. It is possible to have the spacers installed in the negative air spring portion of the can.... which would make your shock likely feel like crap. Remember; after refilling w/ air, it takes quite a few cycles of the shock to fill the negative air chamber.
    The odd sound you are hearing @ 15% sag is air passing through the negative air weep hole in the air can. All shocks do this. Some are more noticeable than others. You'll also feel this if you s-l-o-w-l-y cycle the shock past that point in its travel. Try the same thing on some other bikes and you'll feel the same (or similar) thing.
    As for the sag, those shocks tend to require more than body weight in psi for correct sag. I weigh 135lbs and run 165psi to get 30% sag on a Giant Trance.
    I work on this stuff for a living and everything you're saying actually sounds normal. Of course, I say this with only hearing your description and watching a video of your shock.
    Good luck.

  8. #8
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    Following up: we ended up visiting a not-so-local bike shop for their opinion, the first mechanic we spoke with was "no way it should be like that, it's faulty" but the second more experienced fellow noted that it may be just the interaction between the bike geometry and shock. He advised to try higher pressures, and indeed a bloke from SRAM got back to me and suggested basically the same thing (and also mentioned about how the various tunes should be selected for a specific frame design, though I have no idea how you're supposed to do this when you're fitting a shock aftermarket... Emails to the Merida distributor in Australia have gone unanswered :-( ).

    Armed with this advice we simply upped the pressure in the shock, and after a bit of experimenting my son's now happy with the setup with ~4 rings and about 230 psi.

    Stubbie, good point re. the ring positions and the negative weep hole, and seems you're quite right re. it the shock working as expected.
    Rgds,
    Ben

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