I tried to do the manual cranking thing when our gear casing broke and would no longer engage the jack leg post so as to hold it in place. It just flopped around in the propane cabinet. What a giant POC those things are and they price them like they are titanium. ANYWAY, I grunted on that crank until I thought I was going to blow a heart valve and realized that I had raised the RV a mere 1/4" or so. I gave up on that idea and just used my 20T and 12T bottle jacks to lift the RV off of the truck and get it level.
Cheers!
Mike