Looking to find out which weight gear oil to use in my rear axle.

My truck has a Dana 70, 3.54 ratio, and the limited slip differential.

Here's the catch. I'm looking to buy a travel trailer, with a dry weight of 5,700 lbs. Throw in water, propane, and gear, and I'll be pulling somewhere around 7,000 lbs. Well within my weight limits.

I know I can use 75w90 gear oil in the axle. But I've also read here that the guys that tow a lot like to use 75w140 in the axle.

I don't plan on pulling that trailer every week, but I would like to put the better weight fluid in there.

What should I use?

 

I have had 75W140 Amsoil in my Dana 80 for a lot of miles so far and havnt had any issues. I think next time around I will fill the rear with 75W110 from Amsoil.

I believe a little thicker in the rear axle on these trucks helps out quite a bit. Alof of torque/heat especially when towing on a hot summer day.

I would stick with 75W140 or 75W110 fully synthetic.

 

I went with the heavier Royal Purple becasue I inteneded on towing regularly, however, I tow infrequently.

I will still run the 75/140 just in case I start to tow a lot again..

 

Thanks for the input guys. I went ahead and bought Valvoline full synthetic 74w140. It even says on the bottle that it contains the necessary additive for limited slip differentials.

I even checked in the owners manual, and it reccomends the 75w140 for towing.

 

A good quality 75w90 synthetic gear oil has enough friction modifiers to keep gears fine right up to their material failure. Anything heavier has more drag, creates more heat by it's own internal friction(tiny amounts) and has no measurable benefit.
If you aren't going to tow an occassional house or drag sled the lighter wieght is the best choice IMHO

 

You aren't towing much, or very often you say. I would go with a synthetic 75W90. Also you live up north, and it's not as hot there.

 

Ok, I am getting a little confused. I also need to clarify a little more on my towing.

While I don't plan on towing the camper too often, once or twice a month at most, I will be towing it medium to long distances. The owners manual says that "if you will be towing a significant number of miles, to change the gear oil to a 75w140 synthetic to reduce the possibility of overheating the axle".

I definitely don't want to be on the side of the road with my family and an overheated axle.

 

While there is nothing wrong with going heavier weight it really isn't needed.
How heavy is the trailer and how many hours at a stretch do you figure on towing it?
If you are really concerned about overheating I would get a finned high capacity cover like Hy-tec or similar.
http://www.mag-hytec.com/

 

The trailer's dry weight is 5800 lbs. Throw in water, propane, gear, and family, I'm likely going to be close to 8,000 lbs.

Not sure on the hours, depends on how far we go. We're planning on going up to Acadia National Park, Niagra Falls, fishing trips, etc.

 

My camper rarely comes off. The Amsoil 75-90 Severe Gear is still honey colored on the dipstick of the Mag-Hytec after 38K.

I had RP 75-140 synthetic in my '98.5 and it looked like sludge with the same mileage and load. I don't know if that was an RP thing or the thicker viscosity.

 

I think with a higher mileage rear 75-140 might be better. Currently have 235k on original rear and it still works. I switched to 140 after losing the pinion seal in some deep water/mud (got stuck) and rode home 60 miles in the dark without knowing. After flushing it all out good and fixing the seal, put in some Lucas 80-90 in and it was rumbling on sharp corners. I thought it was shot, but I tried out the RP 75-140 and it has been flawless for over a year/about 15k miles, except for some gear whine on the highway. Posi still works. Just my experience!

 

Use thee 75w-140 synthetic oil. The first number, 75w, is the weight of the oil. The second number is the maximum weight the oil will thicken to when heated. It will be fine for southern New England, I use to live in Cumberland, R.I. I tow 9000lb. a 5th wheel with a boat behind it 400 to 600mi at a time and camp at 7100ft where the temp is 18 to 45.

 

After I broke 2 pinion teeth off my Dana 70 I now use 75W140 in my new axle and have my fingers crossed! Im also keepin my eyes open for a Dana 80 that can hold up to the cummins torque. Here is my first dana 70 back when I was learning the in's and outs of these trucks:
http://www.youtube.com/watch?v=JhKhzvb9Ax4

 

If you can find an 80 from 2001.5 up,you'll score disc brakes too.

 

Thanks for the advise guys. Sounds like I won't go wrong with the 75w140.