Have a 2004.5 3500 dually and tow heavy (14,000 lb. 5th wheel).
Plan on changing differential fluid and would like to use 75-140w instead of 75-90w.
Is there any problem mixing these two viscosities if some fluids remain in the axles after draining the pumkin?
Or can I get the old fluid out of axles by jacking each side?

Thanks

 

Try to get as much as you can (jacking) but the minor amount left may lower you to 74.9-139.9. I wouldn't worry about it, they're both synthetic.

Cya

 

I would think that if you stay with the same Manufacturer of fluid you would be even more safe. I have a PML cover with drain bolt and switched from the 90 to 140 AMSOIL.

 

No need to stick to the same brand, any 75-140 you choose will mix fine with the residual fluid.

Nick

 

I went from 75W-90 to RP 75W-140 about 6 months ago with no problem. I will be going with Amsoil 75W-110 in a few weeks. I figure if I go with a little lighter weight it might help my M.P.G. just a tad.

 

I switched my 03 to Redline 75-140 with no problems, no jacking...

The dealership recommended 75-140 for heavy towing and sold Redline. As long as it is synthetic GL-5, I think you are OK.

I'm about to change the 06 out, and will do the same.

On a side note, I e-mailed Redline to ask if I should use 75-140NS (no limited slip additive) since AAM's don't require additive. The answer was that the additives in the regular 75-140 make the oil more slippery, so although the AAM shouldn't chatter without additive, the additive will reduce friction and temp at the gear contact area so may as well run the regular 75-140...