Differential Fluid Change Question

Nilgai said:
What is the lube of choice? i need to service mine and would like to know what the best is? I have been told y a shop that on my 04 Rubi I do not need a separate limited slip additive and that most good diff lubes already have a limited slip additive in them.
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From the Service manual
• RUBICON 216 FBI (Model 44) - Mopart Synthetic Gear Lubricant 75W-140

Any 75W-140 will work, most are synthetic (and have the LS already ) which is fine cause the Rubicons came with synthetic from the factory. If you do a re-gear you would not want to use synthetic as it gets to hot during the break in period
 
Nilgai said:
What is the lube of choice? i need to service mine and would like to know what the best is? I have been told y a shop that on my 04 Rubi I do not need a separate limited slip additive and that most good diff lubes already have a limited slip additive in them.
Click to expand...
I am about to change the fluids in both front and rear diffs next week.
I have dana 30 and 35 though, not a rubicon. I am going to use Mopar Gear & Axle Lubricant (80W-90, GL-5).
I think for the Dana 44, or in general for heavier use/ or towing 75W-140 API GL-5 is recommended.
 
Thunderhead said:
From the Service manual
• RUBICON 216 FBI (Model 44) - Mopart Synthetic Gear Lubricant 75W-140

Any 75W-140 will work, most are synthetic (and have the LS already ) which is fine cause the Rubicons came with synthetic from the factory. If you do a re-gear you would not want to use synthetic as it gets to hot during the break in period
Click to expand...
i did regear to 4.88 4000 miles ago. so do not do synthetic?
 
It is not good to run a synthetic gear lube during the break-in of new gears. Synthetic gear oil doesn't sink/extract heat from gears as well as a conventional gear lube does. Revolution Gear, Currie, Dynatrac, and many others either require or strongly conventional gear lubes for new gears and axles. Currie had a big issue with the gears in newly installed axles failing during the break-in and traced it to some customers filling them with a synthetic. That's when Currie started requiring the use of conventional gear lubes to keep the warranty in effect.
 
Jerry Bransford said:
It is not good to run a synthetic gear lube during the break-in of new gears. Synthetic gear oil doesn't sink/extract heat from gears as well as a conventional gear lube does. Revolution Gear, Currie, Dynatrac, and many others either require or strongly conventional gear lubes for new gears and axles. Currie had a big issue with the gears in newly installed axles failing during the break-in and traced it to some customers filling them with a synthetic. That's when Currie started requiring the use of conventional gear lubes to keep the warranty in effect.
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Jerry, now you have me thinking. That is dangerous. Does the Lucas 75-140 synthetic have the friction modifier added in? My gears are surely broken in and it is probably time to switch to a heavier weight than the 85/90 hypoid I have been using based upon the temperature here. Would it make a significant difference? Another questions. Does it hurt to add the modifier when in doubt? I am at mercy as to what I can get vs what I want often.

https://www.amazon.com/gp/product/B000IG7PMM/?tag=wranglerorg-20
 
Flivver250 said:
Jerry, now you have me thinking. That is dangerous. Does the Lucas 75-140 synthetic have the friction modifier added in? My gears are surely broken in and it is probably time to switch to a heavier weight than the 85/90 hypoid I have been using based upon the temperature here. Would it make a significant difference? Another questions. Does it hurt to add the modifier when in doubt? I am at mercy as to what I can get vs what I want often.

https://www.amazon.com/gp/product/B000IG7PMM/?tag=wranglerorg-20
Click to expand...


As it is mentioned in their website (link below): "Excellent for use in limited slip differentials." So friction modifier is already added in, as in most synthetic GL5 gear oils (as I have seen stated in many posts, in Various Threads in this forum). You can also see it mentioned in the Technical Data Sheet in the same link.

LINK: https://lucasoil.com/products/gear-oil/synthetic-gear-oil/lucas-sae-75w-140-synthetic-gear-oil
 
Whether or not a GL-5 gear lube has the friction modifier in it only matters IF you have a clutch-based limited slip differential. If you don't have a clutch-based limited slip differential then there's zero need to worry about whether the gear lube contains it or not. But probably 99% of the gear lubes sold do already contain it since that additive is fully compatible with axles whether they have a clutch-based LSD or not.
 
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I just installed new clutches in my Dana 44. They were probably original. A wear item that often gets overlooked, but not if you pay attention here and suffer from OCJD. Just like this thread, I often find solutions for problems I did not know existed.

I have been adding the modifier to Sta-Lube 85/90. It has worked fine and was less expensive.

As I get most of my stuff via amazon and the military FPO/APO, I have been at the mercy of vendors that ship to military postal addresses. Many do not and Amazon themselves can be hit or miss.

I have bought plenty of items that no longer get shipped here. The funny thing is, the USPS shipping cost is only from point of origin to New York.

I think APOs probably have a higher loss or damaged rate.

I'll go ahead and order some new oil and try it. Doubt I'll be able to physically tell the difference, but peace of mind and the contentment achieved by over doing the maintenance is reward enough.
 
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