In the ramp up to the Snotcycle I changed the oil and replaced seals on a few suspension forks and I was struck by a few things. First of all, I am quite careful to catch all the oil that drains out of the fork when I disassemble it. A large plastic bin on the ground below the work stand is a great catch basin. Once the lower legs (sliders) have been removed it is a simple process to clean all the surfaces, pry the old seals out with a large flat head screwdriver from the top of the sliders and then press the new seals in place. Then it is a matter of re-assembling the fork and then filling the fork back up with the appropriate shock oil of the correct weight and the correct volume. As I was pumping the oil into the various chambers of the suspension fork I thought back on all the forks I have overhauled in such a manner and I realized that the amount of oil that had drained out of the fork was perhaps 1/5th the amount that I was re-filling it with. Where in the world did all the oil go? This has occurred even when I have changed the oil on a fairly new fork, usually for the purpose of adding or removing a spacer to change the travel. Even then, hardly any oil pours out into the oil pan. Perhaps manufacturers cut of few corners and save money by skimping a bit on fork oil during assembly in the factory. On the forks that have seen many months of hard riding, perhaps the oil slowly migrates out of the seals and is then washed away when the bike’s owner fastidiously cleans his bike after a few muddy rides? Either way, almost all of the forks I have taken apart have not had the correct volume of oil in them, not even close!
Fox recommends the oil and seals be changed every 50 hours of use. Rock Shox has no stated guidelines but recommends a regular inspection. In every case the forks that I have re-filled have worked markedly better which makes sense since they were running effectively dry before I got my hands on them.
On the scale of mechanical difficulty, changing oil and seals in most suspension forks ranks easy to moderate. Most cyclists I know are fairly diligent about cleaning their bikes and keeping the chain properly lubricated. I would consider this process to be about as easy and not very time consuming. Considering the amount of money some of these shocks cost and the impact they can have on the quality of your ride experience, I think everyone should take the plunge and get oily!
Tom Stokes