Showa Fork Rebuild

By: Clarence Dold
May 1999

At 68,000 miles, it was time to reseal the Show front forks on my 93 K75S. I called the dealer to order the oil seals (my left fork was leaking badly). He suggested that I might want to change the upper and lower slider bushings as well.

I ordered the oil seals, the two bushings, the fill plug o-ring, and the crush washer for the drain.

After doing the job, I realize that I didn't need the fill or drain seals, as I didn't remove either of those screws. I did want a new dust seal for both sides, and the the o-ring for the top cap, as well as a crush washer for the screw that holds the damper rod.

There are two other bushings that are made of some hard nylon-like material that I didn't replace.

I used two special tools. One was a Jorgenson's bar clamp. The other was a length of thin wall pipe, 1-5/8" I.D, larger than the fork slider, smaller than the fork tube.

I looked at the Clymer's manual, then the ibmwr tech pages.

Start by loosening some bolts while the front tire is still on the ground. Axle pinch bolts, Axle bolt, disk caliper bolts, upper and lower fork bridge. The fork bridge clamps should still be snug, to keep the forks from slipping, but breaking them loose before jacking the wheel off the ground is a good idea.

Remove the belly pan, put a jack under the engine, with a block of wood as a pad, and raise the front wheel off the ground.

After removing the front wheel, loosen the bolts going up into the bottom of each fork, then remove the fender and fork brace. Tie the calipers up against the radiator shroud.

Take off the covers over the handlebars, and the handlebars, sliding the handlebars to the side far enough to get at the top of the fork. Pop the fork top plastic cover off.

Thanks to rob@unixguy.com for his suggestion about using a gear puller to press down on the top cap, to release the spring clip. (See http://www.ibmwr.org/ktech/fork-springs.shtml) I'm not as strong as Tom Coradeschi, apparently. I couldn't push down on the cap enough to get the clip out.

I couldn't find my gear puller, but I did find my Jorgenson's bar clamp, usually used for woodworking. In this case, it made a nice clamp, from bottom fork bridge, onto the fork cap. Easy to press down and hold. Then, thanks to Rob for his 'knife' idea, also. Pop the clip downward with a small screwdriver, then put a knife blade in to slide the clip up past the groove and out.

With the top cap out, lift out the top spacer. Remove the fork from the bike, and pour the oil out into a pan, catching the washer and main spring as they come out. I stuck the washer into the spring at the top end where it was supposed to be, as a reminder that the spring's tightly wound coils go toward the top.

As I read the manual, it said to put the fork slider into a vise with soft jaws. I thought about that, and decided to put the fork back into the fork bridge, and tighten the screws a little. Some downward pressure on the fork slider is needed to finish unscrewing the damper rod screw. It might have been possible to do this in a vise, or even hanging the fork upside down to maintain tension against the inside parts, while undoing that bottom bolt.

There is a lower spacer that sits in the bottom of the fork slider, and fits up into the fork tube. This part is now loose inside the fork slider, and must be 'caught' later. The fork should not be allowed to collapse completely now, as this spacer is no longer in alignment with the bottom of the fork tube.

The Clymer's manual didn't cover the Showa front forks. It only covered the BMW-built forks of the earlier K-Series. The Showa parts seem to be simpler.

Pop the dust boot off with a dull blade knife, then remove the clip ring with a screwdriver. Since the bottom screw is now out of the fork, the fork tube no longer tops out against the damper rod spring. The fork obviously slides apart farther, and stops where the lower bushing contacts the upper bushing. Using the fork tube like a slide hammer, yank the fork tube 'briskly' to pull the upper bushing and oil seal out of the fork slider. The lower bushing is at the bottom of the fork tube, and is split. Twist a screwdriver in the split, and pop it off the fork tube.

Clean all the parts, and start reassembly.

Put the damper rod with its spring into the fork tube, and then put the fork tube back into the fork bridge to hold it in position for the next step. Slide an 18" length of coat hanger up through the bolt hole in the bottom of the fork slider, to act as a guide to drop the lower spacer down into place. Then bring the fork slider, with the spacer and coat hanger, up to the bottom of the fork tube, and use the coat hanger to align the damper rod down into place. After removing the coat hanger, the weight of the damper rod is the only force you have holding the damper rod, as you start the screw through the bottom of the fork slider, into the damper rod. Once it is started, you can pull down on the fork slider, increasing the tension against the bolt, to tighten the bolt fully. Some manuals suggest a little sealant on the bottom of the spacer, and on the bolt, to prevent oil seepage.

Take the fork assembly back out of the fork bridge. Putting the top bushing back down into the fork slider would have been difficult, except that I had a chunk of pipe that fit over the fork slider, and inside the fork tube. The I.D. is 1-5/8". I think it is from cyclone fencing, but I'm not sure. It's thinner wall than water pipe. If your pipe is old and dirty, like mine, put the fork top cap into place to prevent debris from falling into the fork tube while banging on the pipe.

Put the washer on top of the bushing, and drive the bushing down. The oil seal is next, on top of the washer. The oil seal has a 'top' and 'bottom'. The 'bottom' is more open, the 'top' has thicker walls. Put the oil seal in place, and use the old seal as a cushion to drive it into place, using the pipe. Put the clip spring on, then the dust boot. Reinsert the fork into the fork bridge, drop in the spring (tight coils up), washer (make sure it falls flat onto the spring), and upper spacer.

The other problem with the non-Showa book is that the oil fill volume is incorrect. Thanks to http://www.ibmwr.org/ktech/fork-oil.shtml - bmwbrian@voicenet.com for providing proper oil amounts. The fork is supposed to have 420cc on a disassembly job.

I measured water into a bottle, and then poured oil into another like bottle to the same level, avoiding having to measure oil with my wife's kitchen tools ;-). With the fork cap still off, the top spacer can be pulled up a ways out of the fork tube, making a nice funnel.

Use the Jorgensons clamp to put the top cap and clip ring back on, and you are done with the forks.

The hardest part of the job was actually getting the grommets back into place in the fender, surrounding the brake lines.

 

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