Wipers are the black rubber rings at the top of the lower legs into which the stanchions disappear. Your forks bob up and down constantly as you ride, and on a muddy day your stanchions will be constantly bombarded with grit. If this grit can work its way down into your seals, it will get dragged up and down by the action of the forks, scouring long vertical grooves in the stanchions, which will allow dirt into your fork and oil out of it.
The wipers serve as a first line of defence against unwanted grit, helping to keep it off the seals. Regularly clean any build-up of dirt off the wipers to stop dirt from working its way down to the seals, which are found below the wipers where they are pressed into the top of the lower legs.
Fork seals have to flex with the movement of the stanchions, forming a tight-fitting barrier to prevent dirt getting in or oil getting out. The seals mustn’t fit too tightly though, or they will stop the fork from moving smoothly. Good seals are one of the most important qualities in a fork. Seals need to be replaced regularly, so ensure that this is done when you get your forks serviced.
Forks used to all come with fork boots, which are flexible rubber gaiters that were supposed to keep the stanchions clean. Besides being ugly, they had a tendency to trap moisture in the area around the top of the lower leg, just where you need it least. Very few forks come with boots now – wipers have replaced them and seals have become much more effective.
After cleaning the fork externally, spray the stanchions lightly with a light oil like GT85, and cycle the forks. This is a fancy term that means, stand next to the bike and push and release on the bars a few times to spread around the oil you’ve applied to the upper part of the stanchion. Then, use a small pick to carefully peel back the top of the wiper and drop in a couple of drops of a heavier oil. Whatever you’re using for your chain will be about right – I prefer something like Finish Line Cross Country. Run the pick gently around the circumference of the wiper, following the pick with a trail of oil. Cycle the fork again and use a clean cloth to wipe away any dirt that emerges.
It’s important not to scratch the stanchion while you’re doing this. If where you normally ride is muddy, it’s worth taking the time to custom make yourself a tool for the task. An old, thinbladed screwdriver, ready to be put out to pasture, can be usefully repurposed and recycled – clamp the last couple of centimetres (1 inch) in a bench vice and bend over at 90 degrees. Clean the blade really carefully and pop into your toolbox. An old spoke, bent at the end and hammered flat, will also serve well. You can buy specially made tools for this purpose, but there really is no reason why you’d want to. Don’t be tempted to use degreaser on the stanchions, even if they’re caked in dirt. It will find its way into the gap between the stanchion and the wiper, and break down all the lubricant inside your fork. So you’ll be nice and clean, but with no bounce.
Cheap forks have chrome steel stanchions. Although heavier than their more expensive anodised aluminium stanchions, chrome steel is smoother and more resistant to nicks and scratches. Some forks are made with both options – for example, a RockShox Recon has the same controls as a Tora, but the stanchions are upgraded to lighter aluminium versions.
“Don’t be tempted to use degreaser on the stanchions, even if they’re caked in dirt. It will find its way into the gap between the stanchion and the wiper”
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
See also bike maintenance tips, tricks and techniques “Inspecting and maintaining your forks for fun and profit”