Just like your car, routine servicing is crucial to get the most out of your fork or shock. Most manufacturers will have routine service recommendations generally between 40 and 100hrs use which for most of us will be annually at very minimum. Although it can cost more in the long run by carrying out regular servicing, it will not only allow for many years of happy trails without spending up big on replacements, but it will also massively improve and maintain a high level of performance for the fork or shock. And that's a win!
'My forks are working fine, they are just due for a service'. It is quite common for a fork to come in for service that feels just 'fine', however the condition on the inside often tells a different story. It is not uncommon to find blackened contaminated damper oil, dry lower legs, perished seals, worn stanchions and so on. So whilst they may be working ok, it is quite possible they are working well below the performance potential.
As you ride your bike, deep within the guts of your fork or shock is a complex array of seals, shafts, shims, pistons and bushings that allow for the complex damper systems within to work. Over time, in normal mountain bike use there will be contaminants such as dust for example that will make their way through the dust seals as they wear. Although it's unlikely that dust will cause any major catastrophies within the fork or shocks internals, it will almost certainly affect it's performance by drying out the inside, and if dust can get in, it will allow oil to get out. Additionally, over time the seals containing the oil within the damper will perish, wear and flatten and in turn loose their ability to properly seal the oil within the damper body. In many fork dampers (Rockshox charger damper, Fox FIT cartridge), there's a rubber bladder that will eventually loose it's ability to properly expand and contract, thus reducing it's ability to assist controlling the flow of oil through the damper's circuit. Eventually, the oil within the damper becomes aerated and that can quickly translate to loss of functionality at the external adjusters.
In rear shocks, this is sometimes referred to as cavitation i.e. when nitrogen or air from a shocks internal floating piston (IFP) chamber escapes and mixes with the oil, leaving you with that squelchy feeling and significant performance loss. (See pic below) The pic shows a cavitated shock damper that has also lost a significant amount of oil through the shocks main (but worn) seal head assembly and adjusters. As a result, there was little function in the lockout lever unit, and the shock rode like a 'pogo-stick'.
In forks, it is all too common to see severe damage to the stanchions, often referred to as the CSU - Crown Steerer Unit, or lower leg unit in Lefty forks. This is usually a result of poor lubrication in the lowers, bushing wear and or seal/foam ring contamination, most of which are avoided by regularly cleaning, inspecting and maintaining reasonable service intervals.
Although these are all replaceable parts, the costs can sometimes get out of control when a fork may end up requiring a service, seals, bushings and new (CSU) stanchions just to get it trail worthy again. For most forks, this part is replaceable, along with new bushings and so on, but it can be avoided with strict routine servicing! Below you'll see some nasty cases of CSU wear
- CSU Bushing Wear
- CSU Bushing Wear
- Lower Leg Wear - Lefty