It sounds like the oil pump drive chain may have fallen off the sprocket. When this happens, there is zero oil pressure. This transmission runs off oil pressure and no oil pressure = no movement. That said, the real problem is that no oil pressure = no lubrication for the engine. That is not
good. STOP RUNNING THE ENGINE IMMEDIATELY OR YOU RISK SERIOUS ENGINE DAMAGE
The official procedure to verify if the oil pump drive chain has fallen off is to perform an oil pressure test with a gauge and special fittings. The test only takes a minute and will confirm this condition right away. But really, why bother? I'll give you and all other Rubicon owners a neat little trick that will tell you in about 30 seconds if the oil pump chain has fallen off. Just make sure you follow this warning... ***** THE RUBICON'S OIL PUMP PUTS OUT 150+ PSI OF OIL PRESSURE. MAKE SURE THAT NO ONE IS AROUND THE TEST PORT AREA. ALSO, COVER THE TEST PORT AREA WITH A BUCKET IN CASE THE OIL PUMP DRIVE CHAIN HAS NOT FALLEN OFF *****
Look to the left front side of the engine for a small bolt. This is the oil pressure test port sealing bolt. Remove this bolt. Usually, this bolt is removed and an oil pressure gauge is screwed into the engine block. You don't have an oil pressure gauge, so what we'll do is simply cover the test port with a bucket (in case the oil pump chain has not fallen off) and start the engine for 5 seconds. It's very simple - if oil shoots out of the hole, the oil pump chain has not derailed and there is another problem with your Rubicon. If no
oil comes out of the hole, the oil pump chain has fallen off the sprocket. Here is the location of the test port sealing bolt.