75w85 rear differential gear oil what are you using

[Texasgrillchef]

For you guys that have changed their rear diff fluid did you stick to motorcraft synthetic 75w85 gear oil? Or use something else? Redline? Lucas? Amsoil?

Feline makes a 75w-85 gear oil available at summit racing. It has lubrication modifiers in it as well. It’s like around $27 a quart

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[Texasgrillchef]

How much oil goes into the m220 rear differential

 

[Ducati1098]

How much oil goes into the m220 rear differential

 

[Felix808]

Valvoline synthetic in the squeeze pack.

Valvoline 75W-140

Yep

 

[Bird Dog Off Road]

Differentials are a bit different (at least from my experience). First of all, I would not run a "weird" viscosity like 75W-85, I would run a 75W-90, 75W-110, or 75W-140--but obviously, this is something that each person must decide. I have a lot of experience with the rear axle in the Bronco because it is the same axle that is in the Jeep Wrangler. Dana specifies 75W-140 in the front and rear of the Dana 44 Advantek whereas the OEMs reduce that in the quest for more MPG. These axles run hotter than previous generations and typically have less oil capacity, though Ford has more sense than Jeep in that area and specified about 2QTs in the rear versus Jeep specifying 1.6QTs in the rear.

Next, they generate more metal than any other axle I have experience with and generate it for far longer than say a Ford branded axle like a 9.75" or a 10.25" axle. From my experience, most Ford branded axles are fully broken in by 15K miles and from that point out produce less and less wear metals per mile. The Advanteks are not like that--they keep producing a substantial amount of metal for longer. Hence, I would change the oil in the axles no later than 5K miles and for the rear, would change it again at 10K, and once again at 15K to get all of the wear metals out.

The Jeep Dana 44 axles had serious issues with failing locking differential modules and until recently did not sell it as a spare part, when it failed, the entire axle was replaced. I have not seen anyone on this forum complaining about that for Broncos, so I will assume that Ford had more sense in that area as well and epoxy potted the sensor to prevent the oil from contamination and ruining it.

Now to the oil, Ford is specifying a conventional oil in the front axle (80W-90) and a synthetic in the rear (75W-85). The API specification for gear oil is API GL-5 and I feel confident and comfortable with using a GL-5 specified oil versus the Ford specification (but I am not recommending that anyone take my advice). For me, I will probably run 75W-110 in the front and rear of my Wildtrak. 75W-110 is the upper viscosity that 75W-90 used to be before the SAE J306 tables were redefined to split the 75W-90 range into two ranges. I feel equally confident in saying that if someone is towing with their Bronco, they should be using 75W-140 in the rear axle as Dana specifies.

As to oil choices, for 75W-110 it is limited to a few brands whereas 75W-90 or 75W-140 are very common. Castrol, Mobil 1, or Valvoline are all good off the shelf choices for those two viscosities.

Hope this helps!

my rear locker didn’t work from the factory. Was told it was a bad solenoid and it took the, 13 months to get it fixed (ended up replacing the entire rear end). Not sure if it was related to metal since it was brand new though. Late build 2021.

 

[Combustion_King]

i run 75w-140 in the front and rear all season with out any issues, i use both lockers, and drive on and offroad of various terrian.

 

[JT58Bronc]

It's so good to see a post like this and the one for "changing fluids early". Regardless of what you use- 75W-90 or 75W-140 it's most important to just change the fluid and not leave it in there forever. The average person does not even know what differential fluid is, never mind changing it. I am getting close to doing mine- will do it at 15K and use 75W-90 Mobil 1.

A side note that differentials are pretty rugged in general and can take a lot of abuse. I have a 87 Chevy Squrebody I am restoring. When I first got it 2 years ago, the first thing I did was change all fluids. The rear differential fluid was so dirty and like sludge. The fill port square drive plug was completely stripped, fluid had not been checked added in quite some time. I had to drill it out and it and it would not budge. Only when I restarted re-tapping it with a smaller fill plug pipe tap did the fill plug come out. Anyway, I had to fill and flush it a second time after driving it a bit the fluid was so darn dirty. Now everything is fine, rear end is quiet like new- new fluid 2X, new rear diff cover, gasket and fill plug.

 

[JohnnyBronco]

From experience selling and servicing Japanese tractors you have to be careful when switching to what you think is normal compared to what is specified.

I don't recall of the exact weight was 75w-85 or 70-80 but it was not at all like 75-90. It was an oil unique at the time to home country and we were instructed and successful using hydraulic transmission oil as a correct substitute for not only front axles and diffs but also mower gearboxes. I had a customer use the heavy oil I. His mower and the increased pressure blew out the seals. Another used heavy oil in the actual hydraulic and blew out the pump seal. Flushed and replaced both with lighter weight UDT and cured problems.

That's why if it says 85 or 90 as the high number in oil weight I would never substitute anything higher. Might as well use molasses

 

[Fordified1]

From experience selling and servicing Japanese tractors you have to be careful when switching to what you think is normal compared to what is specified.

I don't recall of the exact weight was 75w-85 or 70-80 but it was not at all like 75-90. It was an oil unique at the time to home country and we were instructed and successful using hydraulic transmission oil as a correct substitute for not only front axles and diffs but also mower gearboxes. I had a customer use the heavy oil I. His mower and the increased pressure blew out the seals. Another used heavy oil in the actual hydraulic and blew out the pump seal. Flushed and replaced both with lighter weight UDT and cured problems.

That's why if it says 85 or 90 as the high number in oil weight I would never substitute anything higher. Might as well use molasses

Completely different from your examples, There is no pump in a differential that would blow out any seals and they run at extremely high temps so that “molasses” gets thin pretty quick. As stated several times earlier in the thread, Ford is just specifying thinner oils for improved fuel economy, period.

 

[HP11]

After a few highway miles and back road driving for about an hour then home, I took an infrared thermometer to the the rear axle area. I expected higher temperatures to be honest.
Left and right axle bearing area measured 97-degrees and differential cover measured 130-degrees. I measured this twice; once with factory differential cover last week and then after I replaced with an ARB differential cover a few days ago. No towing and ambient temperatures were in the low 80's.

 

[Fordified1]

After a few highway miles and back road driving for about an hour then home, I took an infrared thermometer to the the rear axle area. I expected higher temperatures to be honest.
Left and right axle bearing area measured 97-degrees and differential cover measured 130-degrees. I measured this twice; once with factory differential cover last week and then after I replaced with an ARB differential cover a few days ago. No towing and ambient temperatures were in the low 80's.

That is surprising and good. I can’t hold my hand on the rear diff in my Excursion after a drive. But it does weigh 7k #

the main thing besides lubricating the bearings that high pressure gear lube does is protect the ring and pinion at contact. Thicker is definitely better for this. If I lived in Alaska I might use the thinner oils, but I’m in a warm climate.

 

[HP11]

Totally agree on varying the viscosity based on physical location and type of driving... towing, mountainous etc. Same experience for me in the Mustang not being able to handle the differential for a bit after driving albeit a Torsen differential.

 

[SnowBronco]

I did both diffs today. Added the ford performance diff cover while I was at it. 75-110 amsoil severe gear oil for both.

 

[SWLABRONCO]

Don't forget about the transfer case.

 

[Winds of Change]

I read somewhere that the limited slip additive is not good for the E-lockers.
The additive seems to be in all of them already. Any thoughts?

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