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Shocks are typically only movement dampers; the extending force comes from springs. if your shocks come with built-in springs, you may be able to find different springs that have the same dimensions.Another source for suspension parts is Go-kart places (for heavier parts) and RC car/truck places (for lighter parts.)
The key will be finding a market where something with the specs you want are used and produced in large quantities. Based on your link it looks like you have been searching in the ATV market. You might find some good products in the mountain biking market as well but I know things can get really pricey there. Try searching by specific applications that use similar products such as "mini ATV strut" or "rear mountain bike shock".
If you can disassemble them or even get them apart in a manner that you would be able to reconstruct them replacing the springs might be a good way to go and keep costs down.
As far as specs go there are a lot of variables but the main ones I can think of are: spring rate (which may vary along the stroke), preload, damping coefficient (may be different for extension and compression). Any of these may also be adjustable depending on what shocks you have. I'm not surprised you are having difficulty finding specs as I suspect most of the shocks for ATVs have had little testing outside of does the thing work in application (if they are made in china the manufacturer may not even have an idea what the target specs are ... just what the design they copied looked like ) It looks like the ones you are currently using have a progressive spring rate as well as an adjustable preload. Have you reduced the preload to the minimum setting?
Another idea is to change the mechanical advantage of the suspension mechanism. You could move the mounting point of the shock closer to the pivot of the suspension arm. You could also mount the shock so its axis is more perpendicular to the path made by the point where the shock attaches to the suspension arm.
It sounds like the track is putting a lot of perload on your shocks, can you make the tracks longer?
I'm wondering if the rebound is almost too fast with the shock absorbers that include the coils. Howe and Howe Tech which is a company known for the high speed track systems looks like they don't use coils in their suspension system. Take a look at this video and you can see what I mean
QuoteIf you can disassemble them or even get them apart in a manner that you would be able to reconstruct them replacing the springs might be a good way to go and keep costs down.I agree. I'm trying to figure out how to disassemble these to see if that's an option. It is very cumbersome and requires some advanced tools that I don't have.
It looks like there is a hex on the bottom of the rod eye (inside the spring) is the rod eye threaded onto the rod? If they are permanently attached (or require tools you do not have access to) perhaps you could cut the end of the rod off and either modify the rod eye, manufacture a new one, or purchase an off the shelf component and then reattach the parts.
Looks like the only thing that does damping is the actual spring itself. That's not right, is it? I thought the coils were only responsible for the rebound.
You are correct springs provide very little damping, in terms of system design the damping of a coil spring can usually be neglected. The damper is the chromed cylinder object in your picture. The cylinder is likely filled with oil, typically a piston attached to the rod has a small orifice in it that restricts flow of oil as the rod move in and out. This restriction is what provides the dissipation of energy and the damping. Because the volume inside the cylinder changes a the rod moves in and out shocks are usually "charged" with a compressed gas (nitrogen is often used because it is inert) to take up the remainder of the space not filled with oil. It looks like your cylinders have been assembled by welding the bottom end-cap on so it is unlikely you will be able to see any of the inner working without cutting the cylinder in half. You should be able to feel this damping tho if you move the rod in and out with the spring removed.