No, I didn't think it would be a big job either except for the disassembly of the axle. Remind me again what fluid you use? Maybe I should just spend two days on this and be done with it. I don't even think an overflow is needed with two vents.
If two vents work like I think they should, I agree you will not need an
overflow tank. Now you see why the designer opted to tolerate the
the pressure spikes inside the axles, rather than deal with trouble-prone
venting. As an aside, my ATV has a vented rear final drive & the vent hose
goes all the way up to the handle bars. As the unit got older, the vent
hose cracked down by the final drive, and it took in a lot of water.
I use GL-5 gear oil. We went thru this before when I posted about
rebuilding my early 4300 axle.
I know this is offensive to JD true believers who want to use the hyd oil
specced in the manuals (J20C or J20D). I made this change for several
reasons: I was concerned about the corrosion I saw in my axle, after
9 y of THF being in there. There have been lots of changes to this axle
in just the 4 or 5 years of production. All seem to be made by Spicer (the
inventor of the U-joint), though the earliest ones are unmarked. They are
not made by Deere. OTOH, Kubota and DaeDong do seem to make their
own MFWD axles, and both spec gear oil, and both companies have very
reliable axles. I have not met any JD engineer or other employee who knows
anything about the lube choices they made. (I do ask them at the giant
exhibits at the tractor shows.) I am more comfortable using gear oil for
this low speed conventional gear final drive, but everyone should make
their own choice.
As for the access to inside that axle, that only requires removal of the
4 bolts (photo), and possibly the tie rod end. The shaft slides right out.
You can see the dipstick in there.