how do i disassemble the final drive on a john deere 70D excavator
What's the problem with it?
it's leaking oil and part of a big o-ring is exposed
The complete drive assembly will need to be removed including the motor. It's fairly easy to do. There's heaps of info on this forum about this and how to replace the Duo-Cone seal. Fair warning though, a failed seal can be caused by other factors like worn bearings etc, be prepared.
If you want any proper help from someone like MG, you're going to want to post the serial number.
Is the drive only leaking gear oil or are you losing hydraulic oil as well ? If only leaking gear oil you have the option to replace the duo cone seal without removing the final drive housing from the machine. May save you from fighting a bunch of rust in the frame. Referencing the parts screenshot below. Drain the final drive oil . Remove the planetary pinion assembly #25, gear #17 , shaft #35 and planetary pinion assembly #16. Drive the dowel pin #13 (that locks the nut to the ring gear) inwards until it is clear of the nut #12. Support the drum #6 and sprocket #7 before loosening the nut. You will not likely need a socket to loosen the nut when disassembling a couple of raps with a bar will usually get it loosened. (You will definitely need to fabricate a socket to torque the nut to spec when going back together). Spin off the nut and remove ring gear #11. Remove drum , sprocket , (2) bearings #4 and duo cone seal assembly # 5. . https://partscatalog.deere.com/jdrc/sidebyside/equipment/63405/referrer/navigation/pgId/2950 .