09 1500 QC Hemi with 3.92 LSD. A few weeks ago at 40,000 miles I changed front/rear diff fluid. For the rear I used two liters of Mobil 1 75W-90 LS gear oil, no other additives as this oil includes the additives.

In the past week or so I've noticed a slight gear whine coming from the rear. Today was driving with the rear slider window open and noticed that the noise was much louder and definitely coming from the rear. The noise seems to be relative to the overall speed (faster = higher pitch and louder). I pulled off and crawled under to check what was going on. The diff cover itself felt pretty warm. I pulled the fill plug off to check the fluid level and it was a little below below the hole in the cover, so its not leaking.

What the heck happened to my diff? Is it f@cked? Did I do this to it? Is failure imminent? I'm the second owner of the truck so no lifetime powertrain wrty. Arggggggh.

 

I know you stated the oil you used has the additive in it. But does the oil meet the specs that the Differential Requires? The LSD does require the friction modifier additive, so if I had done this I would of put in the exact oil needed then added the friction modifier separately... my

I have the 3.55's w/ an open diff. so I'm not required to add the friction modifier...

 

Well, you definitely did something stupid. The truck is supposed to have 75W-140 and you put in 75W-90. Stop driving it and put the right oil in immediately.

You need a synthetic 75W-140 that conforms to (MS-8985). Valvoline 75W-140 meets that spec and contains the LS additive already.

 

Although Dodge specs 75w-140 in the rear and 75w-90 in the front, using 75w-90 isn't about to do in the differential, especially in just a few weeks.

The "track" guys around here ALL run either 75w-90 or at least 75w-110 for slightly less resistance and better times. They just change it more often.

Now I'm NOT condoning the use of a thinner oil than the manufacturer recommends, just stating that I've know MANY who have and not had a problem.

A thinner oil will allow you to hear a whine more distinctly than a thicker lubricant. It's very possible this issue has been present for a while.

How warm is "pretty warm"? A diff should be fairly warm, but not "HOT".

You should pull the cover and do a thorough inspection ANY time you hear a whine as soon as possible. IMO you have a problem in the differential, but I don't really think YOU caused it.

If you are sure you have no warranty then the last place I'd bring it is to a dealership. Find you a good, reputable axle shop in your area. You'll get a better over-all assessment, probably better work and for sure get away for at least half what the dealer will charge you.

I had a buddy quoted $2200 for a rear gear swap in his 4x2 Ram at his local dealer last year and my local 4x4 house charged him $675 FOR THE SAME JOB!!!

 

CORRECTION - I did use the 75W-140 in the rear. I did both front and rear at the same time. I used the Mobil1 in the rear and Lucas Oil in the front. I still had a little of the Lucas Oil left over because the front capacity is a little less than the rear. I just checked the bottle in the garage, and the left over is 75W-90 Lucas Oil, which means the Mobil1 75W-140 went in the rear.

At any rate, I'm going to go get some more fluid and do the job again. I'll try to post some pics of the inside.

Yes, the diff cover was warm to touch, but not hot. The part that I thought was strange was that the fluid inside the case wasn't nearly as warm as the case was.

 

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kiggy74,

Mobil gear oil isnt as good as people might think, thers tons of test results on-line, check it out.

Just my opinion, go with Valvoline gear lube (Syn 75w 140)
Comes with some additive, but you will need to add some more additive if you hear/feel chatter coming from the rear LSD diff.
If you dont hear any chatter, then do not add anymore additive to the rear diff.

I quit using mobil products for several reasons, its not as good as they say it is.
Valvoline shows me proof not only in tests, but real world results from what i see when i look inside of everything i use their products in. I`ve NEVER had ANYTHING fail on me using valvoline products..., but mobil & lucas products...yesssss, many failures.

Lots of info on-line guys...!!!!
So before some of you start the bashing on me, do some homework & research.

Amsoil...??? I dont believe all their tests, they hype up the results when they do tests.
Of course THEIR test results are goona look good on THEIR oils, its their oil, their tests.

RedLine "SHOCKPROOF" Gear Lube...???
Yup, i use it in my harley, (bike is 11yrs old 40,000+ miles)
My trans is now ALOT quieter, and shifts FAR better now than it did when it was new.
Next gearlube change on my diff`s, seriously thinkin about trying the RedLine SHOCKPROOF lubes.

 

M1 did not kill his differential. That is what I have in mine, all is well. I did however add the modifyer even though it "had it" in there.

I think we are ignoring the obvious... 2 liters, or litres if you are Canadian.... That is about 67 ounces. The Chrysler 9.25 rear is closer to 72 ounces for capacity. Not having enough in it will surely cause the issue.

 

I originally put in 2.0L of Mobil1, service manual calls for 2.2L. I got a hard time believing I'm hosed over 0.2L of fluid, but what the hell do I know.

I refilled using the Valvoline and added a little of the friction modifier as well. Noise is still present. Gears in the diff still look fine. Going to find an axle shop here in town, still sounds like crap.

 

Running it 5 ounces shy, can starve the pinion and axle bearings of lube. Sometimes in certain case`s, new oil can actually make things worse, especially if run at to low of a level.

M1 Side Note:
When you change the rear gearlube in your truck again, watch for the black sote coming out with the old gearlube, then thank M1 for it being there. It will also have a bright metallic sheen to it too, there again, thank M1 for that too. I`ve been thru this more times than you know, i switched to valvoline lubricants, not an issue since. Your truck, your money, your choice.... just sayin from experience with the difference between the two different lubes.