I am changing the front and rear diff oils on my 2005 Ram 3500 CTD. I am going to use 75W140 in the rear diff, but should I go with 75W90 or 75W140 in the front?
Any help would be great.
Thanks

 

I'd go with 90 up front, make sure it's synthetic all around.

 

Here is thought for you. You make your own conclusion. 50K miles on Amsoil 75/90 gear lube. Check it at 100K miles. 3:73 rear ratio. I replace the old with new, guess what I use QTip to check the used lube vs the brand new on a very clean white paper towel. I could hardly see the difference. I'm impressed. Use only qualitative lubricants in your truck on everything and you won't be sorry. Lubricants are cheap, repair bill are high.