I'm confused. I have a 04.5 4x4 2500 with 10,000 miles. I changed the differentials at 1000 miles with Mobil 1 75-90 synthetic-easy job, no problem. Being **** I'm fretting about changing them again and have found searching the archives some contradictory information. On 7-6-04 one of our members said he talked to Bob Dunn at AAM and was recommended to use 75-90 full synthetic GL-5 fluid. On 8-21 the same member posted that he had called Bob Dunn and Bob recommended 75-140 synthetic GL-5. I've tried several times to call Mr. Dunn at the # posted (1-800-299-2953), and have been unable to get an answer. I e-mailed the member of this forum but his mailbox is currently full, and I've called two the the DC dealers in my region and got two different answers. One "parts department" guy recommended the 140 wt, saying it just "made sense" to use the heavier oil when towing, (which I do. ) The other dealer's service manager looked up their service bulletins on this matter and said the 2500 rear diff took 75-90 synthetic and the 1500 rear diff took the heavier 140!! The manual recommends 75-90 synthetic of course, and in my 2000 I used 140 synthetic for towing.
I'd appreciate any help as far as other's investigation of this matter. Thanks!! Bill

 

I'm getting ready to change mine and going to put in it what the books says, 75w90 gl-5. I can get 75w140 for about half the price of the 75w90 but still sticking to what books says. I have read others put in 75w140 if towing heavy. Maybe others can give you an answer.

 

I followed those posts also. The guy at my dealership said they recommend GL-5 75-140 and it would not void the warranty, so I put in Redline, but it sounds like dealers vary on this.

I think I would do whatever is recommended by your dealer (the one who would handle your warranty problem, if you were to have one).

 

Follow the manual and you can't go wrong.
It states " GL-5 SAE 75W-90 Synthetic. Limited-Slip AAM Axels DO NOT REQUIRE a limited slip additive" Change the fluid every 15k miles

 

I agree with supergewl that way if something goes wrong they cant blame it on the fluid

 

I got one question, if changing out the fluid, what is the negative effect of just using a pump to suck out the diff fluid and refilling. Compared to, pulling the covers off and draining it that way and then refilling?

 

A couple of thoughts:

1. You can get more of it out if you drain it, and probably more of the more grundgy stuff that settles out at the bottom of the diff along the inner gasket. You might not be able to get that stuff out with the sucker.

2. I think its easier to loosen a bunch of cover bolts and let the fluid fall into a pan rather than mess with the sucker.

 

Thanks Bula! When my time comes, I am going to use the wrench technique. This will be my first, I've always had the dealer do it. It does not look that difficult, unscrew, drain, wipe, screw back on, fill, check level, plug it.

 

Yeah, its not that hard. If you loosen all of them but a bottom/middle bolt, and save it for last it won't drain til you made a few turns on that one. You don't even have to remove the cover if you don't want.

When I did mine, I used an electric impact wrench to spin them all loose - simple, quick and clean. Then I spun them on til they seated, and torqued them in place.

As I recall, there was some interference in getting to a couple of bolts at the top of the front diff - but it wasn't a biggie.

Don't forget the GOLDEN RULE: Never drain anything until you're sure you can remove the fill plug.

 

I like that Golden Rule. Been there,done it! Thanks..