there is a mechanical brake [w/electric release] on the electric motor that drives the screw gearset. it holds the motor, which through the gears holds the screw from turning. at work we have those screw jacks too, but we rarely lift loco's with them other than for wreck repairs. we have a large drop table for trucks and fueltanks, and 2 smaller ones for wheels/tm combos, swing hangers... but i don't like going under the jacked up units too.. Copyright 2008 Jerry DeBene
