Well...how tight is fully tight?......Now there's a good question. It's not always obvious. On an off-road car, such as the Nitro Evader, they are a pain....you really have to tighten them.....very tight. To test, tighten the slipper on the spur. Now hold the vehicle down and put a lot of force on trying to turn the spur. The differential should not slip. Now lift the vehicle up off its rear wheels. Hold the spur from turning. Now turn one of the rear wheels. The other rear wheel shoud smoothly turn in the opposite direction wihtout feeling any crunching or grinding noises. After you have it adjusted, remember to loosen your slipper to factory specs (or adjust so that it slips under very firm pressure with the rear wheels held from turning). On on-road cars, such as the NTC3, it's less critical and the instruction manual should be sufficient despite knowing wether fully tight is where you think it is.