I learned a real lesson last week, when the electric jack would not crank down the left jack on the 5th wheel. Tried the manual crank and it would not crank the left jack down either. Since I was already at my destination and the RV was still connected to the truck, I called a mobile tech. I took it apart, and found that the shear pin in the top of the jack had crushed the washer and had everything in a bind. The Mobile tech fixed the problem, and charged me $150. But stated the obvious:
"WHEN WINDING UP THE JACKS DON'T BOTTOM OUT THE JACKS. MARK A SAFE LINE AND STOP AT THAT POINT." My dealer told me to run the jacks up until they bottom out. Doing this repeatedly, crushed the washer and bound everything up. This should work on any electric jack.