What gear oil in the differentials?

Heres my setup:
- HP30 with 4.88 USA Standard gears and an Aussie locker
- 29 spline 8.25 with 4.88 USA Standard gears and a limited slip

The rear has a nice little whine, so Im going to pull the covers and check the backlash on both diffs. If backlash is in spec, Im thinking some heavier gear oil could be beneficial.

Anyways, what weight oil should I use? I have 80-90 in it now and was thinking of 140? Should I just stick with 80-90? I was informed by the guy at autozone that 80-90 was the wrong oil according to the computer. But should I go by what chrysler says, or what U.S.A. Standard says?

Also, Do I need to add any friction modifier for my limited slip and Aussie locker?

I run a HP30 with USA Standard 4.56 and OX up front and an 8.8 LSD in the rear, so it's a similar setup. It's best to run a high quality full synthetic gear oil. I have always been told to run 80-90 for my setup. I'm currently running Mobile1 75-90 as I only paid $7 a pop. All of the synthetics I have found locally have the friction modifier already added. I just run that in both front and back. Did you change your gear oil after the first 500 miles of re-gearing? Yukon/USA Standard recommends changing your gear oil after the first 500 to get rid of any metal particles and phosphoric coating shed in the break-in process. They claim to void your warranty if you do not.

I doubt that a different weight of gear oil will "fix" a gear whine.

I know that the guy at AutoZone is trying to be helpful, but he is actually clueless.

Yes, a clutch type Limited Slip needs friction modifier. Some gears oils say they are for use with Limited Slips, I prefer to add friction modifier.



Cherokee Fluid Capacities

Engine Oil
-2.5L (4cyl) - 4.0 Quarts (3.8L)
-4.0L (6cyl) - 6.0 Quarts (5.7L)

Cooling System
-2.5L (4cyl) - 9.0 Quarts (8.5L)
-4.0L (6cyl) - 10.5 Quarts (9.9L)

Automatic Transmission
-4.0L (6cyl) The AW-4 Automatic Transmission uses Transmission Fluid labeled Dexron-III/Mercon.
- Drain and Re-fill = 4 Quarts (3.8L)
- Filter and complete fluid exchange = 8 Quarts (7.8 L)

-2.5L (4cyl) Chrysler/Mopar Automatic Transmissions use ATF+3 or ATF+4 Type 7176

Manual Transmission

Chrysler now recommends that 10w-30 motor oil be used in Cherokee manual transmissions

-AX-5 5 speed manual - 3.3 quarts 75W-90 GL3 or GL4 (NOT GL5 or GL5 compatible as incorrectly stated in some Owners Manuals)
-AX-15 5 speed manual - 3.32 quarts 75W-90 GL3 or GL4 (NOT GL5 or GL5 compatible as incorrectly stated in some Owners Manuals)
-NV3550 5 speed manual - 2.1 quarts Mopar fluid part # 04874464AA or Snychromax (meets Mopar MS-9224 specs)

The NLGI specs are important - typical NLGI GL-5 gear oil carries added sulphur used as an Extreme Pressure (EP) lubricant. Especially when heated, sulphur is antagonistic to yellow (copper-based) metals - and the synchronizer rings and any bushings in the AX-15 are bronze. Most synthetic gear oils are rated GL-5 and are listed as "safe for use with yellow metals."

Unlike API specs (to API Service SL/CJ-4,) NLGI Service specifications are not reverse-compatible. Well-stocked parts houses will have both NLGI GL-3 and NLGI GL-5 mineral-based gear oil in stock all the time.

If you want to use a synthetic (RedLine, AmsOil, etc.) either check the back of the bottle or check the manufacturer's website to make sure it's safe for use with yellow metal - using sulphur-bearing gear oils usually results in draining your synchronizer rings at your next fluid change...

Transfer Case
-NV231 Part-Time (Command-Trac) - 2.2 Pints (1.0L) Dexron III/Mercon

-NV242 Full-Time (Selec-Trac) – 2.85 Pints (1.3L) Dexron III/Mercon

Front Axle
-Dana 30 - 2.5 Pts (1.2L) SAE 75W-90

Rear Axle
-When equipped, Trac-Lok Limited Slip rear axles require 4 ounces
of Friction Modifier Additive

-Dana 35 - 3.5 Pints (1.66L) SAE 75W-90
-Dana 44 - 4.0 Pints (1.89L) SAE 75W-90
-Chrysler 8.25 - 4.4 Pints (2.0L) SAE 75W-90

For towing and off-road use SAE 75-140 synthetic

I use the kind that's thick and stinky.

Darky said:

I use the kind that's thick and stinky.

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Yeah, really. What is up with the smell?

BTW I don't run synthetic, but only because that stuff will find a way to leak.

I run Amsoil 75w-110 ft/rear. Its a full syn so no modifier added (unless you want)

i use 75-140....nice and thick.

75w140 here

I run 80W-90 in my D60s.

Jump This said:

Yeah, really. What is up with the smell?

BTW I don't run synthetic, but only because that stuff will find a way to leak.

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I love the smell.

I don't run it in my Jeep 'cause it is to costly, but if it is going to leak it'll leak either way.

Jump This said:

BTW I don't run synthetic, but only because that stuff will find a way to leak.

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Damn right it will

Though I have it in my tranny, engine and power steering and all 3 have leaked at some point. The atf +4 from Valvoline isnt bad though. the leftover went in the PS.

dyno or full syn doesn't matter. IF there's a leak, theres a leak.

Johnnie Walker said:

dyno or full syn doesn't matter. IF there's a leak, theres a leak.

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What I was getting at was the act of paying extra to use synthetic, is very ironic that it somehow ends up leaking all over ur garage floor. Most causes it's ur fault like not sealing the tranny pan properly but I've seen other cases

if it says "gear lubricant" or "gear oil" i use it

i can't hear any whine over the rest of the noise my jeep makes.

yes, add friction modifier if you have a limited slip

I ran Lucas 75-90 up front and 75-140 in the rear. I feel you get what you pay for even if I only paid 8.99 at autozone...

I run cheap run of the mil oil from advanced auto, with all the chnages I've made I'm glad I went with a cheap regular oil over syn.

i break and change too much stuff to run expensive oil.

and it always seems to find a place to leak out anyway

If you have a whine, it is unlikely a thicker oil will get rid of it.

ktm racer 419 said:

if it says "gear lubricant" or "gear oil" i use it

i can't hear any whine over the rest of the noise my jeep makes.

yes, add friction modifier if you have a limited slip

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agreed. i use the weight the owners manual recommends. i dont spend big coin on fancy oil. my idea is that its all got to be made with the same minimum standards... proper maintenance is going to do much more for your diffs than throwing "better" oil at it.

If any of you care to read a report on lubricants. Here.

NorCalChris said:

If any of you care to read a report on lubricants. Here.

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Makes me wanna drain my diffs and add amsoil