Rubicon Dana 44 Gear Oil Recommendations?

The factory calls for synthetic in the Rubicon and that's what I've used and will continue to use unless and until I put some aftermarket axles or lockers in the LJ. I know that others have stated aftermarket manufacturers such as Currie specify non-synthetic under penalty of voiding the warranty but for an OEM axle I'd go with what the OEM specifies.

AndyG said:

I see both synthetic and non synthetic recommended ... with my leaning toward 75/140 non synthetic .... thinking the synthetic may help the lockers slide better theoretically ...

What is the best route , changing my brakes I. Fluid today .

Thank you ,
Andy

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I have been a strong proponent of conventional gear lubes for years, after reading of tests that finally proved our gears run cooler when lubed with conventional gear lubes. In fact many well-known axle builders like Currie require their axles run only on conventional gear lubes to keep their warranties in effect. Gear manufacturers like Revolution Gear specify ONLY conventional gear lubes in their instructions.

But because I drive a Rubicon I let myself get talked into using a synthetic gear lube during the break-in of new gears last year. My new gears started a horrendous whine 900-1000 miles later, on the way back from Death Valley. Revolution Gear sent me a set of replacement gears under warranty and I took my Jeep to well-know expert/guru of regearing. As soon as he pulled my gears out he became very agitated and exclaimed they had been overheated and accused me of having used a synthetic gear lube. He was right, I had... against my better judgement. He made it very clear that he has seen too many issues with overheating in axles filled with synthetic gear lubes and made sure he made his point to me to only use a conventional in the future. When I said I had been told Rubicon axles supposedly had a different lube flow design that required a synthetic, he laughed and said that was a bunch of "bullshit".

Not to mention that the gentleman who fixed my gear problem (Martin of Mobile Gears) is probably the most respected R&P gear guy in SoCal, even Revolution Gear was happy when I told them who would be installing my new R&P gears. Martin set up the new gears, refilled the axle with a conventional 85W-140 and life has been good ever since.

The first time I was told about the conventional vs. synthetic gear lube thing, it was during a face-to-face conversation with John Currie maybe 15 years ago. He told me how they were starting to get an unusually high number of new R&P installation failures... gears THEY had installed and knew they had been correctly installed.

Currie then figured out the failures were only with axles the customers had filled with synthetic gear lubes which at the time made no sense. From the damage to the gears, they knew it was heat related... as was with my failed gears. They used an IR temperature gauge to measure the diff housings and observed that the housings filled with synthetics were cooler than those filled with conventional gear lubes. So they figured it can't be from the synthetic gear lube. Months later with more failures and repairs being taken care of under warranty (it's getting expensive for them) they still felt they had a heat problem. So they built a test jig so they could measure the heat of the gears directly. What they found was, when measured directly at the gears, the gears running in the synthetic gear lubes were running significantly hotter than those lubricated with conventional gear lubes. That shocked them since the common knowledge back then was gears lubricated with synthetics run cooler. The research finally figured out that the synthetic gear lube is not as good at extracting the heat out of the gears as a conventional gear lube is. The diff covers were not getting as hot when a synthetic was used because the synthetic wasn't carrying the heat out of the gears and to the diff housing and covers so it could radiate out.

Once Currie and other high-end axle builders figured that out, and they were all shocked at what they had learned about the use of synthetic gear lubes, they immediately changed their instructions to say to use only conventional gear lubes. After that their warranty repairs dropped back down to where they were before their customers started using synthetic gear lubes.

I know some people and shops claim synthetic is ok but when I read Revolution Gear's instructions, Currie's axle instructions, and hear a gear expert yell at me after he sees the condition of my newly installed gears last year, all agreeing to run a conventional gear lube in my axles, I'm back with my strictly conventional gear lube mindset. I don't care if it's a Rubicon axle or a non-Rubicon axle.

Jerry Bransford said:

I don't care if it's a Rubicon axle or a non-Rubicon axle.

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Apples and oranges.


I guess it's a miracle that my OEM gears haven't disintegrated in the last 120,000 miles.

L J said:

Apples and oranges.


I guess it's a miracle that my OEM gears haven't disintegrated in the last 120,000 miles.

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You're very correct that it's apples and oranges... OEM gears come ready to be driven on right out of the factory, no break-in is required. Your OEM gears were thoroughly lapped by Dana Spicer before they were installed at the Jeep factory and were ready to be driven on from day-one. They don't need to be set up or broken in. A synthetic gear lube can be used with them.

Non-OEM/non-factory gears don't come thoroughly pre-lapped like the OEM gears do and they need a full setup which then work-hardens the gears where they mesh against each other. It's during the break-in process where they get hotter. The extra heat caused by use of synthetic gear lubes can harm the gears during that break-in process. Once the gears are broken in, you can run a synthetic if you insist. Talk to a R&P manufacturer like Revolution Gear if you still don't believe any of this.

This is copied from near the bottom of RGA's gear break-in instructions at https://www.revolutiongear.com/ring_and_pinion_break_procedure

"(Recommended gear oil is an 85-140W, Non-Synthetic, GL5 grade or Higher, Name Brand Oil. "

They probably know what they're talking about.

AndyG said:

Thank you. I have felt like the factory synthetic recommendation was to ensure smooth movement of the lockers.

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Not at all, it makes zero difference to the lockers. The choice of gear lube is all about the gears, not about the lockers which are happy with anything that is suitable for the gears.

Don't get the impression that good quality conventional gear lubes are not slippery enough for smooth locker actuation or operation. That's not even a factor.

From my 2005 owners manual

AndyG said:

...just like it's generally not recommended to use synthetic for new engine break in.

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That turned out to be an old wive's tale Andy. Many new high-end cars come from the factory with synthetic engine oils in them.

twistedlv said:

From my 2005 owners manualView attachment 78143

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Why yes, it does say exactly that. I actually have that same manual myself. If you want to just run exactly what that says for the OEM gears the factory installed you will have no problems.

AndyG said:

Would that be similar to the earlier post where it was mentioned that factory tolerances are so good that synthetic is not a problem... For example a factory engine could use synthetic but something rebuilt in a guys garage might need to have conventional oil start with?

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I can't say, factory tolerances vary enough that I'd wouldn't even venture a guess. Engine rebuilders have their own views on lubricants to use during break in.... as do axle builders and ring & pinion gear providers.

So what brand conventional diff oil is the best to go with? What is Trulock axle? Does a Rubicon require additive?

correction Trac-Lok

Carl Kocurek said:

So what brand conventional diff oil is the best to go with? What is Trulock axle? Does a Rubicon require additive?

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Carl Kocurek said:

correction Trac-Lok

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Any major brand is fine. I use Valvoline myself but I'd just as happily use NAPA, Torco, Mobil, Castrol, Shell, Pennzoil, etc. or even Walmart's brand. Today's major brand gear lubes are all very good quality.

Your Tracloc limited slip differential does require an additive which is a friction modifier. But 99.9% of all the gear lubes on the store shelves already contain that additive so you don't need to buy and add it separately. You can verify if the GL-5 gear lube you're looking at has the additive by what it says on the back label. If the back label says something like "Compatible with limited slip differentials", that confirms it already contains the required additive.... don't add more. Most gear lubes contain it since that additive is fully compatible with all automotive axles.

great info thanks.

Most of the gear oils on the shelves here in Honolulu are NOT compatible with limited slip differentials. Only a select few have the additive, despite most being rated GL-5. Probably because everything here is already expensive so most people want the cheapest option. Just a hunch...

However, the Rubcon has True-Loc (not Trac-loc). Trac-loc is a limited lip differential, True-loc is a true mechanical lock. The manual mentions both because the manual is not specific to the Rubicon.

I bought Castrol conventional gear oil for my Rubicon and it seems fine. The cheapest thing would have been O'Reilly's brand oil in bulk. I paid a little more using Castrol because I've had great luck and experience with their products from motorcycles to manufacturing equipment.