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Thread: Dropper post service

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    Default Dropper post service

    I inherited a DNM dropper. It's a relatively unknown brand from Taiwan that sells this post for $140 on Amazon. It was given to me because it failed in short order on the previous owner and he got sick of dealing with the company for a warranty. You can pump it up with a shock pump but it drops immediately under andy weight and stays down.

    I contacted the manufacturer to ask about service instructions andnthe said - I kid you not - to spray WD-40 on it. If that does not work, I have to mail it to them in Taiwan and pay $150 to have it serviced. $150 plus shipping for a $140 post. They also said that I cannot service it because disassembling and reassembling it requires a special jig that only that have. It looks like I could take the bottom off with a pin spanner and a strap wrench, but there's a warning sticker on the bottom that says not to take it apart.

    I can build wheels and service air forks with confidence, so I would like to take a stab at this thing. Even it I can't make it functional, I like taking things apart to see how they work, so it could be a fun dissection project.

    Since I don't have experience servicing dropper posts, what is the worst that can happen if I take it apart? Have you encountered dropper posts that would be dangerous to take apart? I just want to see this thing's guts, so long as it's not going to remove one of my fingers in the process.
    Jonathan - Austin, TX
    A Thorn in Your Sidewall

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    Default Re: Dropper post service

    Let all the air out of it. Put some goggles on and start taking it apart. Don't point it at yourself and you should be fine. Keep your mouth closed, just to be on the safe side.
     

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    Default Re: Dropper post service

    goggles, check.

    Jonathan - Austin, TX
    A Thorn in Your Sidewall

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    Default Re: Dropper post service

    20180330_205012.jpg

    DNM rep said "don't take it apart, we have a special jig to do that in Taiwan." stick on the bottom says "do not disassemble". so I took it apart. it was not that hard, and nothing exploded.

    however, there were no service instuctions anywhere, so I am not 100% certain I put it back together the right way. it's going in the trash. this whole experience has turned me off from dropper seatposts. too much drama. rigid froks and seatpostseses for ever.
    Jonathan - Austin, TX
    A Thorn in Your Sidewall

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    Default Re: Dropper post service

    I'm not exactly a super dropper fan boy but they have their place. Many out their are pretty easy to service and are well supported. I wouldn't write the category off because of one bad experience with a company that won't realistically support product.

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    Default Re: Dropper post service

    There are only 12 parts ... how hard can it be to reassemble and see if it now works?
     

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    Default Re: Dropper post service

    Quote Originally Posted by mack_turtle View Post
    this whole experience has turned me off from dropper seatposts. too much drama. rigid froks and seatpostseses for ever.
    Have you ever tried to service a shifter? Man, those things are the worst. Shifterless 4EVAH.
     

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    Default Re: Dropper post service

    Quote Originally Posted by lala View Post
    There are only 12 parts ... how hard can it be to reassemble and see if it now works?
    Except I have no idea how long it will "work" until it fails me 12 miles from home. I don't think it's worth the hassle anymore. I put it back together and it still does not hold air.

    I have disassembled and rebuild old LX shifters. Both of my bikes are singlespeed, though.
    Jonathan - Austin, TX
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    Default Re: Dropper post service

    I'll give droppers another shot at some point. It seems out of place on a rigid singlespeed, but I won't knock the experience before a actually try it. It's just too bad that this company refuses to support their product and I am enjoying talking shit about them.
    Jonathan - Austin, TX
    A Thorn in Your Sidewall

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    Default Re: Dropper post service

    Quote Originally Posted by mack_turtle View Post
    I have disassembled and rebuild old LX shifters. Both of my bikes are singlespeed, though.
    I used to use a rigid singlespeed as an excuse for being a broke teenager and sucking as a mechanic. Then I got older and much, much faster on gears and suspension.

    Also, I took apart a 1994 Hyundai Accent, and can’t put it back together, and it’s not an M3 so all automobiles suck. I could go on?
     

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    Default Re: Dropper post service

    Quote Originally Posted by Applesauce View Post
    Also, I took apart a 1994 Hyundai Accent, and can’t put it back together, and it’s not an M3 so all automobiles suck. I could go on?
    I am sure that mechanical problems with your Hyundai Accent in 1995 did not require that you ship it back to Korea for the exact cost of a brand new one, and you didn't have to diagnose mechanical issues completey blind. professional mechanics and the public would have access to some sort of manual for that vehicle.

    I conceded that this experience does not mean that all droppers suck and that I will give them a chance. it was just a lousy first experience for me. my commentary stands: when a company makes a "disposable" part that would be easily serviceable if they would provide some sort for support, that sucks. how hard would that be to provide a diagram? throw us a freakin bone here.

    sorry if I came in here with a chip on my shoulder. my frustration is with this manufacturer. just looking for pointers at this time.

    to anyone who has serviced a few droppers- does that one look like anything in particular that I can use as a frame of reference for this one? I don't know where to start with troubleshooting WHY it's not holding air. I am just looking for a frame of reference since I don't have an infinite amount of time to spend fiddling with it when I could be riding.
    Jonathan - Austin, TX
    A Thorn in Your Sidewall

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    Default Re: Dropper post service

    I've rebuilt front shocks. Very simply the reason that piston arrangements like this stop holding air is that the things that are involved in preventing air from escaping (or control the rate at which air moves from one chamber to another) are worn, blocked by crud or destroyed. So the places to check first are o-rings and valves. Looks like there is some sort of ball-valve, perhaps with a spring - hard to tell from the photo - I would make sure that's working correctly and not sticking somehow and not opening or closing at the right moment. And there are quite a few o-rings, so any one of those could be worn down smaller than required and leaking air. Looks like there is also some sort of a top cap - if the threads of that piece have any role in holding air or if there is a missing gasket for that part, then that might be something you'd have to solve. And then finally you have to look at the larger parts and figure out whether the barrel or the piston itself is misshapen in some way that allows air to leak no matter how good the condition of the seals. Bent, gouged, dented, or whatever.

    I think what Applesauce is telling you is that the first thing that gets dropped (no pun) by a manufacturer when they try to lower the price on a part is rebuild-ability, because that cuts out a bunch of expensive engineering time and design work that would have to occur. To an engineer, assembly, disassembly and re-assembly are all different (though related) design problems. As a result, on some of these less expensive parts, the mere act of disassembly will alter the part enough that it will no longer function, because they were never engineered to be re-assembled, let alone disassembled. Which is kind of ironic, because the more affordable parts are more likely to be purchased by budget minded customers who are also more likely to be interested in rebuilding worn equipment for the same reason they bought a more affordable part in the first place.

    As you hinted at above, the ultimate response then is simplicity - the fewer gizmos and mechanisms on the bike, the less expensive it is to ride and maintain.
    Last edited by j44ke; 04-02-2018 at 08:37 AM.
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    Default Re: Dropper post service

    Quote Originally Posted by j44ke View Post
    Very simply the reason that piston arrangements like this stop holding air is that the things that are involved in preventing air from escaping (or control the rate at which air moves from one chamber to another) are worn, blocked by crud or destroyed...
    Pure gold, thank you.

    Yes, the spring that goes at the top is missing in the phot, but I still have it.

    I have two remaining issues:

    1. The pin that holds the actuator at the head of the post was stripped out - the 2.5 mm broach could not be turned and it was too small for any of the bolt extractors I had available - and was destroyed in the process. So I need to find a way to replace it.

    2. I cannot access the anti-roll pins in the post to see if they are damaged. I think those may be outside of the sealed system and have no bearing on how well the system seals, though. So it might not matter.

    I will keep experimenting with this and try to make it work, more out of curiousity than neccessity. I don't trust it enough to put it on my bike in the end. I'll probably get a basic post from a relaible brand.
    Jonathan - Austin, TX
    A Thorn in Your Sidewall

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    Default Re: Dropper post service

    Almost all dropper posts work differently. (The similar exceptions have gas charged cartridges that look like the struts that hold your trunk up, and they look pretty similar, but will all have different bushing and chassis seal-arrangements.) I gather you haven’t taken apart very many hydraulic circuits, or you’d know how different one can be from another: if “dropper posts” were universal, for instance, you could read a Reverb service manual and slap this puppy back together in no time. Likewise for my M3 manual and my Hyundai (which, praised jeebus, I’ve never actually come anywhere near).

    I have NO idea how your post works, and if I don’t, I would venture that you’re asking on the wrong board (maybe try MTBR...those guys seem to love dissembling brand-new garbage parts). Did it have a significant volume of oil in it? Ever? Should it have oil in it? If it should, the reassembly is going be an order-of-operations thing, because you’ll need to have just oil in one place and just air (most likely) in another. But again, these cursory instructions won’t help you, as you’re flying fully blind.
     

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    Default Re: Dropper post service

    Quote Originally Posted by mack_turtle View Post
    Pure gold, thank you.

    Yes, the spring that goes at the top is missing in the phot, but I still have it.

    I have two remaining issues:

    1. The pin that holds the actuator at the head of the post was stripped out - the 2.5 mm broach could not be turned and it was too small for any of the bolt extractors I had available - and was destroyed in the process. So I need to find a way to replace it.

    2. I cannot access the anti-roll pins in the post to see if they are damaged. I think those may be outside of the sealed system and have no bearing on how well the system seals, though. So it might not matter.

    I will keep experimenting with this and try to make it work, more out of curiousity than neccessity. I don't trust it enough to put it on my bike in the end. I'll probably get a basic post from a relaible brand.
    Well, sometimes thinking simply gets skipped over, so....
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    Default Re: Dropper post service

    For the price of a Brand x ascend post I would not try to rebuild another one.
    I used and x -fusion hard for 2 years and tried to service it (thank god I wore goggles), and later just bought a brand x that is heavy but works very well for $115.
     

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    Default Re: Dropper post service

    Happy with my 115$ Tranz-X too which I believe is pretty much the same thing as the Brand-X. It doesn't require to be pumped thus I believe it is spring actuated. Feel free to educate me if that's not the case. Spring works for a long time, do not leak nor do they require maintenance. I think this is the way to go for droppers.
    Last edited by sk_tle; 04-16-2018 at 10:09 AM.
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    Default Re: Dropper post service

    Quote Originally Posted by sk_tle View Post
    Happy with my 115$ Tranz-X too which I believe is pretty much the same thing as the Brand-X. It doesn't require to be pumped thus I believe it is spring actuated. Feel free to educate me if that's not the case. Spring works for a long time, do not leak nor do they require maintenance. I think this is the way to go for droppers.
    Some kind of closed cartridge I understood. Again, really like the post so far.
    Together with "easy out" pedals , it saved me from tip overs that would have ended ugly.
     

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    Default Re: Dropper post service

    I have a Marzocchi Atom-80 in the barn that hasn't seen a shock pump in 5 or 6 years, and is ready to ride. An air spring ain't necessarily high maintenance.

    Coil springs are real nice for having a low threshold of activation (small bump compliance), but is that a must-have for a dropper post?
    Tödd Höllând

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    Default Re: Dropper post service

    Quote Originally Posted by rabo View Post
    Some kind of closed cartridge I understood. Again, really like the post so far.
    Together with "easy out" pedals , it saved me from tip overs that would have ended ugly.
    I stand corrected then.

    Quote Originally Posted by thollandpe View Post
    I have a Marzocchi Atom-80 in the barn that hasn't seen a shock pump in 5 or 6 years, and is ready to ride. An air spring ain't necessarily high maintenance.

    Coil springs are real nice for having a low threshold of activation (small bump compliance), but is that a must-have for a dropper post?
    No I was merely thinking about the low maintenance. Before the TranzX I was using a forca400, 3 position spring actuated one. This time I'm sure it was spring actuated because I actually took it appart and rebuild it once. The spring made for a much faster upward movement than my current TranzX or the reverb and other dropper I used at the time on test bikes. People seemed to have concern that such a dropper could hurt their genitals because of the speed and loud noise it did when reaching the top, but in reality while fast when unloaded the thing wasn't strong enough to hurt.
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