Gross gear oil @ 8k miles

[ShadowsPapa]

People are often concerned about the dark appearance and 'unique' smell of used EP type gear oil. Dark, stinky gear oil is typical

And that's been the case for decades. Doesn't take that many miles for hypoid gear lube to no longer be a nice translucent or dark honey fluid. Black or dark happens pretty easily.

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[rharr]

jac04/SP, I know the smell difference between gear oil and burnt gear oil, very different. Gear oil shouldn't get a burnt smell in 3k.

Here is mopars finest out of my rear diff at 4500 miles...... Coffee color and mildly burnt with some metal filing fully caking the magnet.

Just a follow up. Changed rear axle oil for a second time after 5k miles on it. Wanted to see if it was a oil issue or a axle issue causing the burnt oil. Plus wanted to inspect how much metal goo collected on the magnet from last time. Good news the metal goo is less and the oil (nothing fancy, shop bulk Philips 66 gear oil.) wasn't as nasty/burnt smelling or as dark.

Here are some pics of the drained stuff. (don't mind the chunks in the pan, i didn't wipe it out first, i just wanted to capture color)

and for all the busy bodies, yes i pulled the cover this time and hosed out the housing with brake clean. But it was hardly worth it, no debris/sludge, or anything else, just a fine black film covering everything.

The drain recess being the lowest point catches anything and gets drained out when you open the drain hole. Pretty simple exercise and I encourage anyone with a rubicon at the very least dump the factory crap (with all it's crap from break-in) and put in some fresh stuff, just drain and fill, don't bother pulling the cover unless you really want to and that will go a long way.

 

[ShadowsPapa]

I have 3 different gear lubes in bottles in my shop - and I have a 5 gallon bucket with a pump of another brand in my garage. I got curious and opened each up, looked at color and took good whiffs or each one.
Sort of interesting to note that the Valvoline smelled sort of like - well, hard to describe - gear oil smell plus some other smell to it, the Castrol smelled burned and rancid right out of the bottle. The penzoil looked and smelled the most "clean", a clear honey color and a gear lube smell plus maybe a hint of fish.
So if I were to first smell Penzoil and Valvoline first and then was asked about the Castrol, I'd say it was bad, and yet it's brand new (and sitting in my Javelin differential as that bottle is what's left from filling that one after I cleaned it up)

I can understand ATF smelling burned - most people who are mechanics have smelled that smell because a customer brings a transmission that's slipping to be checked out, or they towed with it and overloaded it and got it hot from slipping the clutches.......... but I'm not sure how you'd actually burn hypoid lube. It's made for extreme pressures and heat because the gears slide over each other with a lot of pressure and side movement, no real rolling action.
You'd have to get it really hot to burn it - really hot.

 

[rharr]

Have you not touched a diff after a long trip or a hard tow? They generate heat. Add in traction control devices that use friction materials, more heat is built.

Putting that all aside new gears and bearings seating for the first time, if you want to run that oem oil with all that crap floating in there for 50k be my guest, but I rather take a half hour and 25 bucks in gear oil and flush that crap out for the sake of my bearing and my locker sensor.

For arguments sake, please explain why my front diff oil (same set up as rear) was lighter in color and had less of a bunrt smell when i first changed oils? All things equal the oils front and back should of been the same color and same smell by your logic and just a brand trait. But alas they were not, the rear was darker, and stank like burnt oil, which indicates the early breaking down of the oil and exposure to high heat.

Your 80's tech AMC stuff is a different design, using different casting types/thicknesses and bearing styles and shouldn't be compared to what we have in 40+ years newer axles. You AMC stuff doesn't use ball bearing for pinion bearing for one thing and your motors aren't putting out 250hp of load into the axle.

 

[Josh00333]

I changed mine at the first oil change, or had it done. Seemed like cheep insurance.

 

[ezekio3160]

Ive always wondered about this. Since I pull my camper once a month ive had it in my head that I would have mine changed sooner than later...now 57k miles later...still thinking about it

Wow!!! 57k miles!!!??? You sure enjoy your drives! How’s the JT holding up?

 

[Glad_he_ate]

I requested mine done on first oil change. Told the sm that I tow about 5500 lbs every couple weeks for sometimes several hundred miles. He said and I quote. If you want it done I’ll do it but it don’t need it, I’d keep my money. It’s covered to 100k and jeep says not to do it till 75k. I said even towing ? He said yes if you are truly trying to be proactive do it at 30k or every spring prior to hooking up your camper.
I decided I’d wait till the spring. By then I’ll have towed a few thousand miles and have roughly 25k on the truck.

 

[rharr]

I requested mine done on first oil change. Told the sm that I tow about 5500 lbs every couple weeks for sometimes several hundred miles. He said and I quote. If you want it done I’ll do it but it don’t need it, I’d keep my money. It’s covered to 100k and jeep says not to do it till 75k. I said even towing ? He said yes if you are truly trying to be proactive do it at 30k or every spring prior to hooking up your camper.
I decided I’d wait till the spring. By then I’ll have towed a few thousand miles and have roughly 25k on the truck.

That is the consensus, yes, but I bet that tech hasn't pulled a diff out yet with only 10k on it and looked at the bearings?

my friend and professional mechanic and anal retentive ass-hat did a re gear on a JTR a few months back and the carrier bearing races were starting to get some interesting wear marks on them and not in a good way. It alarmed him enough that he called everyone of his friends with JT's and told them to come in and get fresh oil. He was also alarmed at the amount of metal on the magnets for such low miles.

if you are leasing and plan to move on in a few years don't worry about it, but there are a few of us that hope to have these for the next 15-20 years.

 

[Glad_he_ate]

I was a master tech for many years myself and not saying your buddy didn’t have reason to be concerned. Looks and smell can be and are deceiving. I plan on keeping mine until i require something different could be a year could be 10+ having done gear oil changes by the drum … sometimes several drums per machine I feel confident mine will last till spring then I’ll swap it out. Here is a sample pic of my past career that machine takes 135 gallons of gear oil. Some of the gears and sprockets are more than 30 inches in diameter.
cool equipment but it’ll beat ya up working on large industrial shit.

 

[Glad_he_ate]

Also just curious has you or your buddy done uoa??

 

[rharr]

Also just curious has you or your buddy done uoa??

No , Used oil analysis (UOA) was done, not worth the time/cost when UOA costs more then just flushing with fresh oil. For hobby folks go do a UOA, but when running a business it's better to go with your experience, especially when material/effort costs are so low. My ghetto UOA was my follow up thread from above. Does the fresh oil i put in at 3k look/smell better now at 8k then what was first pulled out; yes it does with less metal on the magnet observed.

The wear marks on the races indicated contaminated oil, aka excess metal in the oil. Plus the amount of metal filings on the locker sensor magnet was also alarming and likely why folks have locker engagement issues.

 

[Gren71]

Wow!!! 57k miles!!!??? You sure enjoy your drives! How’s the JT holding up?

Lol I actually do very much enjoy driving! Helps that I have a 40mile commute to work every day.

The Jt is holding up great! Though ives stuck to some lessons learned from other jeeps…

I corrected all of the geometry as close to oem as possible after a moderate 2in lift. And I use close to stock size tires and wont add a mess of unnecessary heavy bumpers and such. Keeps the wear and tare down a bit IMO.

 

[Maximus Gladius]

Also just curious has you or your buddy done uoa??

I’ve done oil analysis’s of not only my Gladiator diffs but also of my previous truck, 2017 Tacoma Sport diffs for reference.
The metal wear of the rear diffs is much higher in both vehicles when comparing with the front diffs. Hence, you would conclude the sheer pressure of the gears is less up front than the back which then explains the front oil will not be as dark as the back. I will post the lab results.

 

[ShadowsPapa]

The metal wear of the rear diffs is much higher in both vehicles when looking at the front diffs.

There is no load on the pinion and ring gear for the front differential unless you are using it in 4 wheel drive. In fact, the pinion and ring gear don't even turn so there should be zero wear up front unless you engage 4x4 mode and drive it.
Only the carrier gears, the spiders/pinions inside the carrier turn when in 2 wheel drive mode.
That being said - that front ring gear should last forever on a truck like mine.
There's almost never any load on it, it's only turning when I engage it.

The rear differential is carrying the load of pushing the truck any time you are driving it while the front ring gear just sits there.

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