Replacing Fork Seals

Leaking fork seals are more than a messy eyesore. Let them go long enough and the oil can ruin brake pads and, when the fluid's gone, the fork's internals will begin a nice 60-grit dance. You don't want any of that.

Fortunately, fork-seal replacement is generally uncomplicated. As always, the task is easier if you get your tools and supplies ready. You'll need whatever tools are necessary to remove the fork tubes from the bike, plus a hex socket to fit the socket-head bolt securing damping rod or cartridge. (Most Japanese sportbikes use a 6mm or 8mm hex.) It's important that the hex portion of the tool is long enough to reach through the axle casting without fouling the access hole underneath. Have two fork seals at hand; you never know when you'll ruin one during the install or, more likely, decide the job is so much fun you can't resist doing the other seal at the same time. Have a sufficient quantity of fresh fork oil at the ready, too.

Start by getting the fork leg off the bike--did you remember to crack the fork cap while the lower triple clamp bolts were still tight?--and giving it a thorough bath with a parts washer or contact cleaner. With the fork cap still in place, take your hex driver and insert it into the damping-cartridge hole; give it three or four good whacks with a hammer (1) to help unseat any thread-locking compound. Loosen but don't remove the bolt just yet. Go to the other end of the leg and remove the fork cap (2). Drain the fork oil through the top, and take careful note of the orientation of the spring, washers and spacers. Remove the fork cap from the damping rod, then remove the spring, spacers and washers and set them aside. Next, remove the cartridge bolt (3), make sure you account for the brass washer under its head.

The next sequence will remove the old seal. First pry the dust seal from the top of the fork leg (4), being careful not to gouge the soft aluminum. Underneath this cap you'll see the fork seal proper, secured by an expanding clip set inside a small groove (5). Carefully pry this clip out. Squirt some contact cleaner into the recess to flush out any gunk.What comes next sounds positively barbaric, but it works. Grasp the fork tube in one hand and the stanchion in the other (6). Rapidly, and with moderate force, attempt to hyperextend the fork tube. Did you hear the clank? Good. Keep going until the fork seal begins to move out of the cavity; once it gets going it doesn't take a lot of extra effort to set it free.

Take a moment to examine the bushing (7), looking for cracks or a speckled appearance that indicates grime and metal shavings have been worked into the surface. Clean the exposed parts again.

Now you're ready to install the new seal. Wrap the top of the stanchion with electrical tape (8) and lightly lubricate the inside of the new seal. Pay attention to which end is supposed to go up. (Hint: It'll be the closed end. The side that is supposed to face down will have a small tensioning spring visible.) Carefully slip the seal over the stanchion. Take your time and, if you experience trouble getting the seal to fit, warm it under a lamp before trying again.

To set the seal, you can use any of a number of special tools called seal drivers (Race Tech at 909/279-6655 or www.racetech.com sells drivers for $69.99) or you can improvise. Whatever you use to drive the seal must fit the seal perfectly, with the outer diameter of the tube (or pipe or whatever) just small enough to fit into the slider cavity. If the driver is too small you'll damage the seal. Also, the face of the driver must be perfectly flat and smooth. Ready? Take your tool (9) and use it to gently tap the seal into the recess; keep going until it seats firmly. Inspect it to be sure it's straight in the bore and that the retaining-clip groove is exposed (10). Reinstall the clip and dust seal, followed by the damping rod or cartridge, refill with oil (be sure to measure the level with the spring out and the fork leg fully compressed) and you're just about done.

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