On a Deere excavator 270D LC Do I need to bleed the Hydraulic pump if I drain the hydraulic tank?

Yes, you should purge air before running the machine hard, though "bleeding" here means something different than a brake or fuel system bleed. On a piston pump, running it dry-primed even briefly can score the pistons and slippers before oil ever reaches them, so the sequence matters more than the word "bleed" suggests.

Do this before you rev the engine:

1. Fill the tank to the correct level with the boom/arm/bucket in their normal resting position (not fully retracted, which changes cylinder displacement and throws off your fill level).
2. Crack the fitting on top of each main pump case (highest port) and let oil gravity-feed in until it runs out solid with no air, then retighten. This fills the pump housing so it isn't spinning dry on startup.
3. Start the engine and idle it low for 3-5 minutes before touching any control. Watch the pressure gauges and listen for pump noise, a growling or rattling pump at idle means it's still cavitating.
4. Once idle is quiet, cycle every function slowly through full travel several times at low engine speed, this pushes trapped air out through the cylinders and back to tank rather than through the pump.
5. Recheck tank level after cycling, air pockets collapsing will drop the level, top off as needed.

If the pump rattles or growls past a few minutes of idle, shut down immediately and recheck your top-fill on the pump case, don't push through it hoping it clears, a piston pump that cavitates on startup can gouge the barrel in seconds and that's a rebuild, not a warranty claim.

Hydraulic oil can still be under residual pressure from cylinder weight even with the engine off, so when you crack that top fitting on the pump, point it away from your face and have a rag ready.

Post whether your machine has one pump or two (270D LC typically runs a tandem pump setup) and whether you got any codes on the monitor after restart if you want a tighter check on whether it primed correctly.