First, I admit I'm ****, and uncertainty is hard. The variations in viscosity recommendations for the rear differential (04.5) has been frustrating because the owners manual recommendations are "synthetic 75-90" and there is supposed to be a TSB saying 75-140. I've gone to the "dieselram.info" page and I am suspicious as the TSB 03-001-04-REV.A prints out with the words "Power Door Locks Do Not Unlock The Rear Doors" but then goes into the viscosity/synthetic recommendations for the 04 Druango, Ram Truck and Dakota. It says 75-140 synthetic for the 11.5 rear axle under the 2500-3500 chart as well as 75-90 non-synthetic for the front.
I went to my local 5Star place, talked to parts man "Brian" who is clearly one the the good guys, and looked on his computer at the same 03-001-04REV.A TSB and it states, under 2500-3500, that the rear takes 75-90 synthetic and the front takes 75-90 synthetic. I looked at the computer screen, and the print out pages match the screen and they are different than what I printed off the DieselRam.info page.
Does anyone else have an online reference to this same TSB revision that they could post?? I certainly am NO expert on differential fluids, and used 75-140 synthetic in my Y2K CTD, but I don't want to do anything to interfere with warranty if should ever come to that.
Thanks for listening!! Bill

 

Use the 140.

 

I can relate to your concern. I wanted to switch out the lube in my 6 spd on my 01 a few years back. Before I got to it the trans failed and the dealer fixing it said DC wanted a fluid analysis. If I had anything but the required in there, I would have lost my warranty.

I also asked about the rear diff fluid on the 04 and Dodge as well as the dealer told me use the synthetic 75/90. I recall reading somewhere that the heavier lube was or is recommended for the rear diff for heavy towing but I never got that confirmed from DC.
Therefore I bought another jug of the 75/90. I feel it would make more sense to put the heavier stuff in for heavy towing especially in the summer.

Scotty

 

There was a TSB concerning the 1500 series trucks that required 75-140 synthetic be used for towing. The 3/4-1 ton trucks have always required the 75-90. I use the 140 in my 01, but we tow in ambient temps that are too high to think about.

 

Here's what I think over this confusion on the weight of gear to run in the AAM 11.5"
If towing heavy or live in the deep south or west run 75w-140. Light towing and living up north 75w-90 is fine.
After scorching the paint off the diff cover I switched over to 75w-140 with a PML aluminum cover.

MikeyB

 

MikeyB has an excellent point so I called my 5-STAR and proposed the fact that I tow heavy, and in hot weather and the 75-140 "meets or exceeds" the GL5 recommendations. The service manager said that was fine, they had others do it in routine maintance at their dealership, and their experience was that STAR would honor warrantee work under those conditions as the 75-90 was the "minimum" recommendation. Thanks to all-Bill