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  1. #1
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    Rear shock oil change...

    Hello everyone.

    After a seven year break I'm back into mountain biking. I went to the dark side during that 7 years and was a full time dirtbiker. But a torn ACL, surgery, and alot of physio has shown me I need to get back on the mountain bike.

    Wow, I'm so amazed at how mountain bikes have changed. Full suspension was starting to take off when I quite, but I was so turned off with these bikes after my GT RTS-2. But it seems like manufacturers have really done their homework and come up with great bushings and linkage systems. I'm really impressed. Part of the reason I got out of mountain biking was my old Kula just didn't handle the downhilling very well. I'm a true XC guy, but downhills is 50% of the ride. So now that I'm getting back into it, I figure getting a different bike is good. So I find out there is a new category called "all mountain". Cool. Heavy for XC climbing, but smooth for XC downhills. So I find a cheap one in the bargain finder. A 2001 Giant XTC AC2. Nice bike. But like everything I own, needs to be overhauled to perform at 110%.

    My time with dirtbikes has taught me alot about suspension. So I figure the first thing would be the rear shock. Surely the previous owner never changed the oil. Well I was right. But the funny thing is I'm trying to find out info on shock oil changes and nothing seems to be out there. Does nobody change their oil on their shocks??? I don't get it. My shock is a DNM backdraft air/oil shock. Seems like a pretty crappy one, but good enough for my comeback. But I can't find any info on this shock. DNM has been absolutetly no help. They suggested I send it back to Tiawan for repair. I don't think so. The shipping would cost more then the shock is worth. So I find myself figuring it out on my own. I just wanted to ask if anyone here has had experience with this shock and knows where I could get a seal kit for it. I'm also trying to find out the correct oil volume it needs.

    Also, why are most of the XC bikes using air/oil and not a coil over shock? I would think a coil would be far better then air.

    Anyway, thanks for your feedback.

  2. #2
    Lost in the Black Hills mx_599's Avatar
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    Quote Originally Posted by renes
    Hello everyone. Does nobody change their oil on their shocks??? I don't get it. My shock is a DNM backdraft air/oil shock. But I can't find any info on this shock. DNM has been absolutetly no help. I just wanted to ask if anyone here has had experience with this shock and knows where I could get a seal kit for it. I'm also trying to find out the correct oil volume it needs.

    Also, why are most of the XC bikes using air/oil and not a coil over shock? I would think a coil would be far better then air.

    Anyway, thanks for your feedback.
    have you ever serviced a motocross shock?

    is this shock you're refering to even serviceable? i would imagine you put as much oil in it as you can, with no bubbles...like a mx shock. i am assuming there is an air bladder...no? if the air and oil mix, that would be a pretty crappy design. are you sure its not meant to be thrown away? can you see where its made to disassemble?

    to answer your other question, most people DO NOT know how to change their shock oil

    i believe many of the shocks use air over coil to save weight.

    if your shock is not leaking oil, a seal change is unneccessary.

  3. #3
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    Most XC rear shocks do not have a servicable oil damper. You used to be able to take some of them apart but the manufacturer wasn't much help with IFP depths and most people didn't have access to nitrogen to re-pressurize the IFP. In the bicycle industry there was not any demand for custom shim stacks, re-porting vavles, or changing oil viscostiy and by the time the damper assembly needed service the bike and shock were outdated. Most current rear shocks have so much external adjustability with high speed and low speed compression and rebound damping, stable platform systems like SPV, teralogic and motion control plus adjustable positive and negative springs that we don't need to do custom valving. Now everything I see has a roll crimped damper assembly and you can't take them apart. It is still very easy to service the air canister on most brands of air sprung rear shocks. I am not farmiliar with DNM so I can't help you there but if you purchase a new rear shock and want to refresh the oil if it breaks down then you should check out the Marzocchi Rocco or Manitou Swinger line, Fox and Rock Shox XC shocks don't have servicable dampers from what I've seen. Cane Creek makes XC rear shocks that are air sprung and air damped that you can adjust and are servicable. Also for some cool suspension tech you can check out www.pushindustries.com.

  4. #4
    The Red Lantern Rev.Chuck's Avatar
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    Unless the nitrogen seal fails all you need to do is pull it apart and clean the seals, wipe out the bore and relube with the proper juice every now and then. Almost like cleaning a mason jar but you need to let the air out first. A bigger service problem is bushings and bearings. They are pretty small on most bikes and wear pretty quick leaving play in the system.
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