[dutton]

Couple things to try. First, when you're shimming, did you shim one gear at a time, ensuring to tighten down all screws and check for wobble/lock up. If not, you want to shim the spur gear first, tighten the box all the way down, check for smooth movement, reopen place, the sector gear in with the spur, tighten the box down, and repeat for the bevel gear, having both the sector and spur gears in place.

If you did that, next question is what battery are you using? A lot of times gearboxes lock up because the battery cannot put out enough power to cycle everything. Try discharging/recharging the battery or using another battery altogether. It helps to try a higher voltage battery in semi-auto.

If that doesn't do it, next thing to check is all the wiring. You want to make sure everything is making a solid contact and not grounding on anything metal. A lot of times it's a simple cut in the protective coating of the wiring that'll cause these problems.

Last thing to try is a different motor. It's quite possible the motor just can't handle it. This can range from needed new brushes, to a defective motor, to a failing motor.

If none of those work, let me know and I can throw some more information your way.