Thanks very much all. Your insight appreciated.

I can follow directions for the lube change, but lacked experiences to know what damage looked like.

As to the foamy milky look....weird.

Googling comes up with answers ranging from:
overfilled
water
friction modifier used (mopar original unavailable, used after market)

Water obviously not possible.

I used brake cleaner on mating surface to clean RTV off to shining surface. It is possible some got in diff (I was careful but a little?)

Also noted it was difficult to remove all existing lube.

It pools at the bottom of the diff and doesn't flow out when truck was level. I used my fingers to paddle out all I could.

No leaks I saw last night. Will check for seeping Friday afternoon, when I do the front diff.

Have many afternoons of scheduled maintenance ahead of me.

Not looking forward to driver side rear V10 spark plug...

 

Sounds like it may have been over filled. Best way to get it right that I can think of is to get the truck level and crawl up under it, remove the plug on the rear cover, put a pan under it and let any excess fluid weep out of the plug hole. After awhile after the excess fluid drains out, put the plug back in.

 

So, first for clarification, when I say 'level' I mean parked in such a way that I can put a level on the pickup bed rails and it's level. This morning I looked at it twice, once, when level - cold...then again after a 30 minute drive.

Cold - fluid was clear and unremarkable.

Warm - I know I said milky before, but upon close inspection in morning light (rather than late afternoon dimming light) I would say..."sudsy". As far as over filled nothing flows out...except after I stick my finger in, a small bead drags out with it down the diff cover...but it's really just a drop, not enough to even make it to the ground.

Picture of 'suds' suds on finger
here you can see the fill level...and 'suds' inside.
Now...a bit more fun...I think the 'suds' are maybe a result of the synthetic oil. When I removed the old stuff it was cold so no telling if it was sudsy before, but I saw no evidence of suds. The truck calls for some 90W oil in back but there's a note about heavy towing and putting synthetic back there - the same stuff that is called for in the front. So I thought "ehh, I tow in the summer - when it's 100 degrees out...sure...why not" the Synthetic wasn't prohibitively expensive anyway.

Well, after checking my rear diff warm, I decided to go ahead and start on front diff, easier to drain when it's still warm from my drive...I can let it drain while I work - then go back out at lunch and finish it up (I work at home, and depending on what I have going on it's easy to do a little work before my work day starts, and then get back out at lunch).

Well, check the fluid before removing the pumpkin, and it looks EXACTLY like the rear fluid...sudsy. So I'm thinking maybe this is something that either:

1) pretty much always looks this way warm.
2) is just how the synthetic stuff looks warm.

So unless that fluid level looked over filled to you guys, in the pic above, I think I'm likely fine.

As to leaking...I opted to buy a fel-pro gasket rather than use RTV (and feel better about that decision after spending a long time cleaning the remaining orange RTV from both surfaces)...I saw no drips this morning, or spots on concrete. After I took it for the drive to warm it this morning I put some cardboard under the rear diff to see if I get any spots...safe to say that if I see nothing in 8 hours of sitting there that I'm leak free?

I'm sure the RTV works well for sealing, but I would rather not have to spend all that time scrubbing and using a plastic scraper trying to get it off again. The felpro went on dry...I just used a little gasket sealent to 'glue' it to the surface of the cover, making alignment easier while I was under the truck.

Thanks everyone for reading the thread and contributing.

Side note, if anyone is ever looking to undertake this for the first time, and reading through this thread. When you remove the cover bolts the cover will almost certainly not slide off, it will be stuck, well glued by the RTV that was previously used to seal things up...and possibly no amount of tapping with a rubber mallet gets it moving. For mine, I put a floor jack under the cover and jacked it up against the cover, with small block of wood to distribute the push and keep from any hard scratching/indenting on the cover...that gets it moving. However, be warned...it's just about impossible to time getting the pan back under there...there will be fluid spillage if you don't plan ahead and line a large swath of floor under the jack and cover.

-Ray

 

If you used synthetic oil then you did not need friction modifier.

Synthetic OR traditional w/ FM but not both. Could be why there's bubbles. I've never seen anything like that.

As for changing the oil, you can always just get a hand pump to remove the old through the fill hole so the cover never has to come off. I'm **** so I do it fully with RTV and wire brush all surfaces for a complete change.

 

Unless the gear lube used already has friction modifier in it, (and, some does, some does not) it still needs to be in there, regardless of fluid used. If it comes already in it, all well and good, if it doesn't SPECIFICALLY STATE the the FM is in there, you need to add it.

 

I saw you could pump it out. But then I never would have seen the inside, and learned as much as I have

 

Double checked the bottle of what I used (incidentally what I used was MasterPro 75W140 Synthetic...Orielly house brand I would guess)...while it says its ok to use in LSD, it doesn't say it has any additives for it.

Given that the front differential which I had not touched, was in the same shape (foamy/sudsy) when warm - I'm less concerned. As I look around the internet I find as many people say "huh?" as I do say "yeah that's normal".

Finally ran into some videos on youtube of folks with clear differential covers...which seems to confirm the idea that things get whipped up in there by gears...
This guy went from normal dark fluid to a mocha foam cappuccino in about 45 seconds.







So I went ahead and drained and replaced my front differential. Same basic experience....spent 3x longer cleaning RTV than any other step.I saw nothing very different than the rear diff in terms of condition, except on the inside of the cover plate, once clean there was some scoring...Pics attached.I ask all you experienced folks...normal wear and tear causes this?

 

You are way over analyzing this. Again those are not scorns, looks to me like build of up oil or a film of something over the years and when the fluid is swishing around in there, it kinda smears that built up, caked up film stuff. All the gears and everything look like they should with nothing obviously wrong with them? Not metal shavings? Nothing to worry about. Fill her up and not worry about it for interval

 

Thanks. Only way to learn... do stuff, ask questions, get answers.

Appreciate all the help.

 

Use a 90 degree die grinder with 3M roloc scotch brite pads https://www.fisheriessupply.com/3m-r...bly-with-shank https://www.3m.com/3M/en_US/company-...3241340&rt=rud

You can get scotch brite pads, sanding discs, bristle discs. They are awesome. You can use an electric drill if you don't have a die grinder.