I wrote up a tension mod for the SideWinder 3D in May of 2000 (back in the Elvene days). If I recall correctly, the disassembly on the FF stick was exactly the same up until you began to disassemble the actual internal mechanism, except that it didn't have a mode switch to worry about. Since I still have the write up, I thought I'd post the first section describing disassembly for you. If it helps you out, great. If not, then... sorry.
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Grue
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Disclaimer - As always, working with electronics requires static safe handling.
Note – for the purpose of this procedure, the front of the joystick is considered to be the direction you would push the stick directly away from you (pitch down) if the joystick were placed naturally on the desk in front of you in use. Even when holding the unit upside down and “backwards” for disassembly, all references to left, right, forward, back, top and bottom refer to the joystick as if it were sitting on the desk in it’s natural position, unless specifically referenced to you instead.
Step 1: examine your joystick. The procedure I describe was used on joysticks marked on the bottom with:
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Microsoft ® Sidewinder ™ 3D Pro
Part No. 63545
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Proceed cautiously in any event, but if you have a different part number use extreme caution. Note the position of the mode selector switch on the front bottom of the joystick so that you can put it back in the same mode when done. (edit-> the mode switch does not apply to the FF)
Step 2: Disconnect the joystick from the computer. Place the joystick upside down in your lap, stick portion between your thighs, with the base resting comfortably in your lap. Orient so that forward on the joystick is toward your body.
Step 3. Locate the first hidden screw under the label on the bottom of the joystick. Press in on the label on the “tion” portion of the word Corporation under the word SideWinder, and you will feel a hole behind the label. Using the very small flathead screwdriver or an exacto knife break/cut open the label at that point so that the head of the screw is visible.
Step 4. Locate the other 2 hidden screws on the bottom of the joystick. Carefully pry up (damaging as little as possible) and remove the two rubber feet at the front corners of the joystick, and place them to the side.
Step 5. You should now be able to see 7 screws in the base of the joystick. Using the #1 Phillips, remove them.
Step 6. Center the mode selector switch exactly between the one and two dot settings. Using both hands (thumbs positioned each side of selector switch) gently lift the plastic base of the joystick up and away from you, and it should freely detach from the rest of the joystick. Note, from this point forward static safe precautions should be observed.
Step 7. (The rest describes how to mod the stick to remove the center slack, which is non-applicable to the FF stick)