Long time viewer, first time posting. I'm getting conflicting answers from my dealer on which fluid to use in the differentials and was wondering what the majority thought. I have an 04 2500HD with the Cummins. Rearend went at 35,000 mile so you can understand my concern.

Changed the front differential 15k ago and they gave me 3 quarts of SAE 80W-90 @ $6 a quart. Went in yesterday to purchase fluid for both front and rear and they brought out 8 quarts of SAE 75W-90 Synthetic @ $25 a quart. Any insight on this would be appreciated. Thanks

 

I can tell ya what I use on my truck. I have a Dana 80 on the rear. It takes just short of 2 gallons. Sometimes I face it down hill to get some extra in there.lol. I have a Detroit locker and have had zero problems. My original Dana 70 had 45,000 miles on it when I swapped it out. I can show ya pics of the carrier if you want. Nothin but 75-90 Hypoid lube. That synthectic stuff in my opinion is overrated. I have a new Eaton E-Locker for the front Dana and it says 75-90 weight gear oil too.

I'm not cheap by no means but the prices on some of this stuff now adays is unbelievable. If it's changed at proper intervals, you will have no problem. If you tow frequently, and it's in harsh conditions (heat and then extreme temp changes at night for example) I would change it at 10,000 miles. My buddy who owns a ford that has billet covers with drains, oversized magnets, mid way AND top fill holes, PLUS you can preload the bearings. It holds almost an extra gallon of lube oil. He does it every 20,000. He's had no problems.

Just my opinion............nothing special.


Good luck.

 

your 04 has an AAM 9.25 front and AAM 11.5 rear, both take synthetic GL-5 fluid in either the 75w-90 or 75w-140. the 140 is only if you tow alot.

I just changed both my front and rear not long ago and used AMSoil severe gear 75w-90 GL-5, the front took a bit over half a gallon and the rear took right under a gallon.

 

As per the manual, it depends on the axle size. *And, since I'm no expert on the sizes available in the 2500's.... of course, Drew did post, he's got real experiance )
Front Axle gets 75W-90 Synthetic (1.75 quarts for the C205F, and 2.3 quarts for the 9 1/4")
Rear Axle gets: 9 1/4" 75W-140 Syn. (2.45 quarts); 10 1/2" 75W-90 Syn. (2.4 quarts); 11 1/2" 75W-90 Syn. (3.8 quarts)
If you have limited slip differential, you have to add 4 oz. of L.S.D. Additive (available at dealer, but thats on the 9 1/4").
$25 for 75W-90 is steep. I can buy that, in synthetic (Mobil 1) for $9/quart. 75W-140, on the other hand, is a little more expensive, around $16/quart.

 

just to add a bit more since you mentioned the LSD. the LSD function in these AAM axels is actualy run by worm gears and not the traditional clutches. with that said no friction modifiers are needed, however, some have reported a howl after changeing the fluids, added some friction modifyer and the howl went away. I dont have the howling some have reported so I'm not going to add any

 

Thanks, that answered my next question, "How would I know if I had to add the LSD additive". I'm going to go with the Mobil 1 GL-5 75W-90 synthetic gear lube. $9 at Autozone. Thanks for all replies.