I got my car together with a used 8 3/4 differential, 741 case. Now I find it is leaking fluid from the pinion seal. Can the flange be unbolted and the seal replaced in the car, or does this get into the whole crush sleeve process? Thanks.

no crush sleeve in the 741, just pull the pinion & tap out the old seal around the perimeter of it & pack around the spring on the new seal with grease to keep it in place (if that type has a spring, been quite awhile) & drive it in. get it started straight then finish driving it with as few strokes as possible (each stroke ups the chances of damaging a seal). keep it going in straight.

No crush sleeve in a 741--you're lucky. Yes it can be done. MATCHMARK the pinion nut to the pinion. Remove the nut,replace seal and return the nut to the same position.

Torquing the nut to spec can be difficult but should result in the nut match mark returning to the same position.

I will add, inspect the sealing surface on the yoke and polish out any irregularities install a sppedee sleeve ( if available ??)
I would also add a bit of sealer to the OD of the seal as well as the splines as occasionally they will leak through the splines.

Blue Locktite the pinion nut for a little insurance.

And pack the seal garter spring with grease, they're known to pop off during installation.

Thanks all. Glad to hear no crush sleeve is involved on this case. I will get a seal tomorrow and install it with grease, sealer, locktite and and a big ole torque wrench.

Don't rely on torque reading, just use a torque wrench to get it close.
Read Pacnorthcuda's reply again.
keyword...MATCHMARK
Make sure you get the nut back in the same location which should give the same bearing pre-load as before.

OK so is the bottom line to get it back to the same turning torque # OR to get it to the same "matchmark" ?

Ideally the torque wrench would click as the match marks lined up.
It's clear to me that the designer specified the torque to fasten the joint properly, thus tighten to proper torque.
You can use the match mark method here, too, and it'll be fine unless there has been some wear that shortens the assembly length. If the wrench clicks before the marks line up, you have a different friction between nut and pinion. In that case line up the marks.

The match mark method is really useful on a crush sleeve setup, it's harder to get a decent torque reading. I also think it was developed by mechanics working on the flat rate because it saves minutes. You don't have to even use a torque wrench. Just tighten 'til snug and then turn nut until match marks line up.

R.

When putting in the pinion seal , it's good to smear a little sealant in that back cavity floor and wall where the pinion seal bottoms out.
Then press in the pinion seal till it bottoms out.

Dog, noted, thank you.

The torque reading is what is required to get it on properly per the FSM
OP, forget the match mark method and torque it to the proper torque

Torque it is!