Safeties are inside the trolley that rides in the track. If there is nothing left in the overhead to pick the car up, you will probably need to crib up to the platform and support the car and sling an disconnect the trolley from the cab, four allen bolts secure the trolley to the cab. When you crib up for the cab, a bottle jack at half extension in the cribbing will allow you to lower the cab a few inches after you raise the trolley. It sounds like one of the cables might have slipped at the drum and is allowing the safety to set. This uses a broken rope safety and either cable being loose will set safeties.