I recently sold my 1999 F500 that had the P-Bone head shock fork.. There was no lock out on that model of fork. Cannondale made 50 or more different models of shock forks with all kinds of tech from coil springs, elastomers, air compression, oil dampening. Just about any combo and amounts of travel.. They don't all have the same features.. Vintage Cannondale dot com has lots of info including a whole section just on forks. You may find your fork has no lock out option. ON some models there is a 1/4" set screw under the knob that adjust tension on the spring. If yo try to remove it, it can come out about as fast as a .22 slug so watch out if you mess with it. There is a special cannondale castle wrench for disassembly that cost $75 -$100, just to take it apart so you can find out you can' t parts anyhow. Plenty of sites about these forks and the issues. Keep it clean and lubed. Water getting in is the enemy.