Re: thunderbolt 800 wont go into gear...
Drop the lower unit once more (if you haven't got it fixed already) and get a feel for how the lower unit shifts. Don't use vise-grips on the splined shaft, a 3/8" (I think) socket fits nicely onto the splines, and you can rotate the shift shaft easily with a ratchet.
The shift cam attached to the shift shaft has 3 lobes that define the gear selection. The cam is free to rotate 360*, but the gear selection occurs only within about 45* of rotation. See attached photo for reference.
Once the cam is in the "free" zone of 300* as you described, it is outside of the shifting region. Continue to SLOWLY rotate the shift shaft CCW and you will feel a small detent. Stop. This is the FWD gear detent. The prop will lock in one direction and ratchet in the other. SLOWLY continue to rotate CCW until you feel the next (more distinct) detent. Stop. This is the NEUTRAL gear detent. The prop will spin freely in either direction. Continue to rotate CCW until you feel another small detent, and this will be the reverse detent. Stop. The prop will be locked in either direction. Do not rotate any further CCW. Now rotate the shift shaft CW back to the neutral detent. Do not rotate the shift cam CW (other than changing from N to FWD or R to N) as you may damage something due to the shape of the cam.
Put the control in neutral and disconnect the shift linkage from the motor. This will allow the upper and lower shift shafts to easily align, as you install the lower unit, if they are slightly out of alignment. Once the lower unit is in place, you can adjust the shift linkage as required at the motor.
