Changing leaking fork seals is vital to the safety of motorcycle operation. Inadequate fork oil and pressure can result in fork dive and decreased braking ability. It can also result in a jarring ride. Changing fork seals requires some tools and preparation, and must be performed correctly. Have tools and supplies on hand, and use caution in handling suspension parts to avoid damage.
Remove the front wheel. Remove the brake caliper, and use a bungee cord to hold the caliper up and out of the way. Detach the speedometer cable from the speedometer drive. Remove the front fender, and carefully remove the axle covers, lowering the front wheel to the ground. Set the front wheel aside.
Drain the fork oil. Using the appropriate Allen wrench, remove the drain bolt from the bottom of each fork, allowing the fork oil to drain completely into a drain pan. Set the drain bolts aside.
Remove the forks from the bike. Before removal, use a large wrench or socket to loosen the fork caps on both forks. Do not remove the caps while the forks are still on the bike. Carefully loosen the four bolts on the triple trees that secure the forks to the bike. Only loosen these bolts enough so that the fork tubes slide easily out of the clamps.
Clear a large clean work area to disassemble the forks, once they are removed. Carefully remove the fork cap and slide the springs and washers from the inside of the fork, making careful note of the order in which they were removed.
Remove the dust cap. Using circlip pliers, remove the clip above the fork seal. Then, using a rapid motion, pull the upper fork tube and the lower fork leg in opposite directions. After a couple of quick forceful tugs, the fork seal should pop loose, and the fork leg should come apart. Before pulling, ensure that the circlip has been removed, otherwise significant damage will result. If the fork seal sticks and the fork does not come apart, do not pry the fork seal out. Seek professional help. Significant damage can result to fork tubes by prying.
Remove the upper fork tube from the lower fork tube, and inspect the bushings. Bushings should be brass in colour. If a silver sheen is showing through the brass, the bushings should be replaced. It is generally a good idea to replace bushings at the same time that fork seals are replaced.
Clean all parts carefully before reassembly, using a parts washer or brake parts cleaner. Inspect parts for damage, and replace any that show significant damage or wear.
Slide fork tubes back together. Reinstall drain bolts using new copper washers on each. Slide the new seal over the inner fork tube, and slide it into place using a fork seal driver, until it is seated firmly in the outer fork tube. Install the circlip on top of the seal, then install the dust cap over it.
Pour in the correct amount and weight of fork oil according the manufacturer's specifications. Reinstall the fork caps as tightly as you can by hand. Slide the fork tubes back into the triple clamps, and tighten the lower retaining bolts to manufacturers specifications. Tighten the fork caps to the proper torque specifications, then tighten the upper triple clamp bolts.
Reassemble the remainder of the front end, following the reverse of the assembly steps. Ensure that the front tire spins freely and is properly aligned. Also ensure that the front brakes are functioning properly.
Take the bike for a test drive, after inspecting your work and completing all steps. Ensure that all braking systems are operating properly and that the front suspension feels firm and does not "dive" on front-end braking. Look around the front end, ensuring that there are no leaks, and check all bolts for tightness. Clean all surfaces of fingerprints and smudges of oil.
Before attempting any repair job, you should have tools and parts necessary on hand. Brakes and suspension components of a motorcycle are vital to rider safety. If you are not confident in doing repairs or maintenance to these systems yourself, seek professional advice or help. It is always advisable to have a good repair manual on hand to aid in completion of this task. Place the motorcycle securely on a motorcycle jack or table, elevated enough to work comfortably on and around the front of the bike.