This procedure is based on my RS250 manual, which also has USD Showa forks.

Remove the springs
• The RS250 manual leaves draining the fork oil until a later stage, but I prefer to get it over with now. The method I've been using is to back out the compression screw at the bottom of the fork leg, then removing the compression valve and draining the oil out the bottom (see the page on replacing fork oil). You need to be very careful not to damage the valve needle. Record the number of turns to fully seat the compression valve before backing it out. After removing the valve, pump the forks a few times to spray out the oil, then replace and tighten the compression valve.
   
• Turn the rebound adjust screw on top of the preload cap all the way in (gently), recording the number of turns. Then turn it all the way out (again, gently) to free the needle from the orifice. Next turn the preload adjuster in to reveal the spring clip on the top of the adjuster rod (anodized blue). Remove this clip, keeping your hand over it so as not to spring it across the room. After removing the clip, you can back out the preload adjuster all the way and remove it from the fork.
• Remove the nylon ring underneath the preload adjuster that retains three pins that push down on the spring. Unscrew the red preload cap completely now. There should be no spring pressure behind it. When it is unscrewed, the fork can be collapsed, revealing a steel preload tube bolted to the cap. This tube is pressing down on the spring and is under pressure.
• To remove the preload tube, it must first be pushed down against the spring while the blue damping rod is held up. When the tube has compressed the spring about an inch, it will reveal a wrench flat on the damping rod that must be held while the preload cap is removed. I strongly recommend you make or buy both of the special tools to depress and hold this tube.
   
  • The first tool grips the preload tube using the holes in its sides and has handles to allow you to push down on the tube with both hands. At 1 kg/mm, you need to be able to apply about 50 lbs to depress the tube enough to get at the wrench flat. I thought about using a couple long bolts, or perhaps modifying a c-clamp to fit in the hole. In the end I just welded up a tool shown in the picture below.
     
  • The second tool is a like a slotted clip, something to just slip over the damping rod under its lock nut to hold the preload tube down so you can release the push-down tool and remove the cap. The clip or plate could be a fender washer, maybe 1-1/2 inches in diameter to hold the tube, with a half inch hole slotted out to the edge to slip over the rod. I was quite lucky, as I had a piece just like this already: the Honda CBR600F3 cartridge forks have a slotted and dished washer in their parts list that serves a similar function (holding down the spring beneath a lock nut). If you order this part, or find it at a junk dealer, it works perfectly. I had a few bent F3 forks lying around.
  
   

  The preload tube has already been compressed and clipped down, revealing the wrench flats on the blue damping rod that you need to expose. Note the use of two tools to compress and retain the preload tube. (Click on image to enlarge and show notations.)

  
   
• I would recommend you depress the tube carefully and evenly, and only enough to get the clip in place. There is something that the tube bushing can get hung up on deeper in the forks (perhaps it can leave the bottom of the tube), and I managed to damage a bushing because I was not careful about this. (At least I think that's how it was damaged). This bushing does not have a separate part number, and an entire preload tube must be ordered if you damage it ($45 a side). To avoid depressing the tube excessively, have an assistant hold the preload cap up and slip in the clip while you depress the tube. Once the tube is clipped down, you can hold the rod with a wrench and unscrew the red preload cap from it.
   
• After the preload cap has been removed, you can once again depress the preload tube with the tool and remove the clip. Release the tube slowly, maneuvering it so it doesn't hang up on the blue damping rod.
• Remove the preload tube from the fork (with plastic spacer and washer above), then fish out the spring beneath it, and finally the washer and preload spacer beneath that. Remember that if you tip the fork over at this point to retreive the spacer, its going to have residual oil in it!
   
• Note that USD forks, unlike standard damping rod forks, will fall apart if the preload cap is off and you lift them by the upper (outer) tube. Don't do this!
   

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