I have a 2006 Ram 3500 4X4 dually with 3:73 rear end gearing, and Cummins diesel with automatic transmission. I am pulling a new fifth wheel trailer that has a GVWR of 16,500. Whenever I pull the fifth wheel I can smell rear end gear lub especially when exiting the vehicle. I had all the fluids changed and the rear end lubricant was literally black. We inspected the "guts" of the rear end and found no indication of unsual wear or any mechanical problems, no pitting or discoloration. We flushed the rear end and put in new fluids with the limited slip additive per Dodge specifications. I am still getting the smell. Could this be caused by the trailer being too heavy for the rear end gearing? Suggestions?

 

Seems to me the 3500 rear end doesn't need LSD additive, even if it has LSD. Not sure if that's the issue, but there it is.

 

The odor may very well be coming from the vent. But make sure the vent is not clogged. Just an idea....

 

Mike, I totally agree, must have read the chevy service manual

 

Worm gear = no clutch packs = do not use limited slip additive.

And yeah, you are exceeding the limit of the 3.73 rear end. Technically you are just over the limit for a 4.10 rear. BUT I know guys pull that much with 3.73s and other than having to worry about the law and their insurance company in case of mishap, they don't have any real problems.

I'm assuming you are using a full synthetic, right? I'd be interested in the actual temp inside that diff while towing. Installing a temp sensor would be best, but just to have an idea, you can shoot it with a laser gun. What are they down to now, about $20 at Harbour Freight?

The HD truck market is amazing anymore. 2500 SRW Rams are rated for over 17,000# with 3.42 rear ends. Properly setup 3500 DRWs are rated for 30,000+ with 4.10s...

 

Thanks to all who have provided me informatin on the possibilities of the gear lub smell. I will try and find info on the need for the additive and if it is not needed, but been added, could that be the source of the smell.

ALso trying to find 2006 RAM 3500 4X4 towing specifications if anyone can steer me to a link.

 

TM, the FSM calls out friction modifier for the 9-1/4 LC differentials in the 1500's
The 10.5 and 11.5 like you and I have calls for 75w90, but normally, 75w140 is what I've installed and the mileages prove me out, my 2005, 2500 has 217K miles on it and the diffs are in great shape. Stay full synthetic, change them at 30K miles.