Replacing fork seals on a scooter dual-arm suspension system can be a bit of a beast, similar to the same work on a motorcycle. Since such dual fork systems basically use the same design, the repair work to replace leaky fork seals generally follows the same steps.
Disconnect the scooter headset from the top of the fork using a socket wrench. Use a crescent wrench or adjustable wrench to loosen the triple tree assembly at the top of the fork unit. Loosen the front wheel axle and brake caliper with crescent wrenches as well. Use a crate or stand to lift the front end of the scooter and suspend it in the air.
Finish loosening the bolts holding on the brake parts, cables, and front wheel assembly. Strip the bottom forks of parts until they are bare. Remove the bolts on the triple clamp that were loosened earlier and pull the fork legs out, one at a time as you work on them.
Pinch the top of the first fork in a vice clamp with padding or brass jaws so as not to damage the chrome or metal. Tighten the vice down a few inches below the top end of the fork. Loosen the fork cap with an adjustable wrench until loose enough to twist by hand. Continue twisting, being ready to catch the cap when it pops loose with the spring inside. Take the internal spring out and drain the fork oil.
Go inside the fork with a damper rod tool and loosen the damper rod from its connection to the bottom of the fork. Reposition the fork so that the outer fork cover is now in the vice clamp. Unscrew the dust seal at the end of the big tube and remove the spring clip underneath. Pull the inner fork tube out of the outer tube cavity. Remove the old bushings from the fork and replace them.
Clean all the separated metal parts of the fork with a solvent cleaner. Remove all signs of old oil and dirt. Look for bad pitting to confirm if a fork tube part needs to be replaced. Use oil-soaked emery cloth to smooth out minor pitting.
Reinstall the damper rod in the fork and tighten it so it won't come out. Install the upper guide bushing into the outer fork tube. Apply a new fork seal on the inner tube and follow it with the dust seal. Refill the fork leg inner tube with the required amount of fork oil. Push the inner fork back into the outer fork tube and try to completely compress it to squeeze the air out.
Pull the fork inner tube out again and insert the adjuster spring, hardware, and cap to keep it in place. Put the inner tube back into the outer tube and take it off the vice. Transfer the rebuilt fork back to the triple clamp on the scooter and reinstall it. Tighten the bolts in the triple clamp holding the rebuilt fork. Perform Steps 2 through 8 for the remaining fork.
Adjust the front fork's sag when both forks are completely rebuilt. Use the pre-load adjuster dials located on the fork tops to determine the setting.
Fork seal replacement should occur when you see signs of fork oil residue appearing on the top of fork tubes.
Be careful to anticipate when the fork oil will be exposed, otherwise you will spill it all over your workspace floor, creating a big mess.
Tips and warnings
- Fork seal replacement should occur when you see signs of fork oil residue appearing on the top of fork tubes.
- Be careful to anticipate when the fork oil will be exposed, otherwise you will spill it all over your workspace floor, creating a big mess.