Hi,
my 1970 Challenger with 8 3/4" rear axle needs new outer bearings. I will just put in new tapered ones, no change towards green bearings. While doing so I'd like to install new seals etc. Does the third member oil need to be drained and/or refilled? Is the oil level high enough to run out the sides of the axle housing when I pull the axle shafts or pry out the inner seal rings?

You won’t have to drain it and it should not run out the sides if it was properly filled to begin with.

Thanks a lot, Suregrip391. I just found a good pic of a 489 third member which confirms it. Drain plug is lower than the axles.

I jack each side up a bit higher than level doing one at a time just to make sure & on a side note the hypodermic needle attachment on your grease gun works good for greaseing the new (or old) bearings. I would do new seals at the same time. EDIT & I do the dr side first then the pass side with the adjuster & get ~.010" end play.

The inner axle seals should stop any gear oil from draining out the sides as long as the rear end is near level

I've never seen an inner axle seal on an 8-3/4".

Stock should have inner seal. If converted to green bearing it may or may not have the seal as it is not required with the green bearings.
FWIW, The photo of the 8-3/4 does not have a thrust button, so would need to run with green bearings.

those big seals are technickly called an inner seal & the thin ones in the 5 hole bolt on flanges are the outer ones but most people dont service the thin outer ones & just refer to the big ones (that are driven in) as the outers cuz they are pretty much on the outer end of the housing.

Inner as in between the bearing and the center section, not that it's anywhere near the center section.

The inner large axle seal is in the housing, the outer is on the axle
I install them in all the rear ends I work on, even with the green bearings to help stop gear lube form leaking onto the brakes and the backing plates

but don't use green bearings

I've had to use the Green bearings(from Dr Diff) to put a 35 spline axle in a 8 3/4 housing along with the Dana 60 inner axle seal with good results

Side question, (and perhaps I've missed it posted elsewhere) but, does anyone have a tuitorial or Youtube link on how to overhaul and diagnose an 8.75? I think mine needs axle bearings but have no idea. Could be the carrier bearings?

I know for some of You this is something you can do in your sleep, but rear differentials are really out of my comfort zone. Any advice would be greatly appreciated.

It's probably best to start a new post describing the symptoms / concerns and we can try to help from there