Ask the Editors: My ATV Thinks it’s a Pogo Stick

April 23rd, 2012 by Jason Giacchino

 
 
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Dear ATVC:

My quad’s rear shock feels really springy- it still seems to be working but the rear of the machine bounces more than I remember over rough terrain. My friend says it means the shock is blown and needs to be rebuilt. I thought a blown shock wouldn’t work at all. Please help.



Sadly we’re inclined to agree with your friend on this one. To understand why a blown shock turns even softer and bouncier than a properly functioning one, let’s take a moment to examine what’s going on inside your ATV’s shocks.

Shocks absorb impact by using the flow of fluid (oil) through stacks of washers that act as valves. When a shock is new (or freshly rebuilt), the system works smoothly. However, like all oils, shock fluid begins breaking down over time. As shock fluid degenerates, it becomes thinner and hence passes through the valving with less resistance than it should.

This is critical because the damping circuits (valves) inside your shock are what provide the resistance not only to impacts causing the shock to move in the first place but also to keep the shock’s spring from compressing and expanding wildly. So why have a spring at all if it’s oil doing the absorbing? The answer is rebound; or the force that allows the shock to extend after it has been compressed. Without a spring, your shock would only work the first time it was compressed.

In addition to the shock’s fluid breaking down inside, the outside of your ATV’s suspension is dealing with all sorts of nasty conditions each and every time you ride. Dust, grime small rocks and sand gather up on the shock bodies then get pushed into your shock’s rubber seals. Acting as gritty sandpaper, these unwanted materials breakdown seals and wipers over time as well, often resulting in the shock’s internal fluid leaking out.

The reason a blown shock feels suddenly softer is that the fluid-driven damping circuit is being bypassed entirely due to one (or both) of the situations described above. In other words, your machine is in fact riding on the spring and the spring alone. No oil damping absorbing the terrain (compression) and likewise no oil damping to slow down the spring’s return expansion (rebound).

Higher end shocks can be rebuilt (oil change, fresh seals etc.) but many budget-friendly ATVs (including minis) offer non-rebuildable units as a cost shavings measure. If that’s the case with your particular quad, replacement is the only option.

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