The only true Dana 80 is in a 3500. You have the Dana 70 which was used in Auto 2500s. Then the 70U (some call it the 70HD) but Dodge called it the 80 and if you look on the pumpkin you will see it says 80 & 70. Everything is a 80 except the axle tubes they are a Dana 70. A true Dana 80 will not neck down at the wheels.

 

The Dana 70HD was a 35 spline Dana 70 used in older Fords but it still used Dana 70 gears, carrier, and bearings. The Dana 70u is a 32 spline Dana 70 used in auto 2500s. The Dana 80 that came in the Cummins manual 2500s is a true Dana 80, gears, carrier, axles and all. Just because it necks down on the ends so they could put smaller hubs on it Doesn't make it a Dana 70. Ford use several different hub designs on the Dana 80 as well but they are still all Dana 80 axles.

 

In telling you my Dodge books even list all axles available for a 2500. They are: 60, 70, and a Hybrid 80/70 which they call the 70U. The only Dana 80 available is in a 3500. I'll even get pictures of a Dana 80 out of a 2500. It has a lot weight rating then a 80 because the axle tubes are not as thick. So it is a Dana 80 with 70 axle tubes but Dodge called it a 70UHD.

 

Once again the Dana 80 that came in the in the 2500 is not a Dana 70U. The Dana 80 has a 11" ring gear, 35 spline shafts, and a bigger carrier. The Dana 70U has a 10.5" ring gear 32 spline shafts, and a different carrier, those parts do not interchange between the two. Multiple sources below if you want to see for yourself.

https://torqueking.com/category/1994...-80-rear-axle/
https://torqueking.com/category/1994...-70-rear-axle/
https://www.randysworldwide.com/diff...ear+Diff+-+4WD
https://www.dieselhub.com/axle/dana-70.html
https://www.dieselhub.com/maintenanc...-80-fluid.html
https://dodgeforum.com/forum/2nd-gen...ram-axles.html
https://en.wikipedia.org/wiki/Dana_80
Dodge

1994-2002 3500
1994-2002 2500 equipped with manual transmissions and Diesel or V10 engines

https://en.wikipedia.org/wiki/Dana_70

Dana 70U/Dana 70B

Dana 70U/Dana 70B
In the 1980s the Dana 70U or Dana 70B was offered. GM, Ford and Dodge all used this axle. This axle had a smaller pinion bearing and mostly have 32 spline axle shafts. The Dana 70U and Dana 70B both have gross axle weight ratings of 7,500 lb (3,400 kg). The 2nd generation Dodge Ram trucks consistently feature this axle in the 2500 trucks with the Diesel or V10 and automatic transmission. This axle was designed for single rear wheel applications.

 

If you read what I said it's a Dana 80 with 70 axle tubes. DODGE called it the 70UHD. I can take a picture of the document that lists the axles available.

 

I have the Dana 80 in my 96 Dually. While it is a heavier unit I don't think it would cause much, if any, extra stress on your transmission. Now if you get cocky and start putting WAY more weight in and/or behind your truck because you have a beefier rear diff... That's where you will start running into issues with the transmission not being able to cope.

 

My transmission 46 is essentially a 47RE. He rebuilt it with 47RE internals. Secondly, the dually was also available in a V8 option, though less common, it does exist. Thank you for your feedback! that project has been put on hold.