Which rear diff fluid do I need for Dana 70HD?

[1989 R3500]

I'm getting ready to buy my parts for the rear differential on my 89 Chevy R3500 dually.
Can someone tell me which diff oil is best? I.e 75/90, 75/140 etc.

I'm probably going with Royal purple or Lucas.

Thanks in advance.

 

[AuroraGirl]

Is that a 14 bolt or is it something else? Most manuals say 80w90 unless in Canada (or just coldser climates) but I guess do you have any modifications like locker or posi? Depending on that miht need additives.

 

[AuroraGirl]

nvm i didnt see your title said dana70hd. do you have an owners manual for that year? if so, it should list a fluid viscosity to use, but the spec it suggests will likely be superseded. gl-5 is what mine asks for

this is from 1989 truck manual. 80w-90 GL-5

 

[ali_c20]

The important thing is that it's GL5 for high pressures in the hypoid gear setup of the differential. 75w-140 if you use your truck for towing and long distances, but it's double the $ as 80w-90.

 

[AuroraGirl]

gl-4 has the compatibility with bronze/copper in old gearboxes

 

[Paladin]

I have exact same differential. Been using Castrol Hypoy-C 80w90, no problems!!

 

[1989 R3500]

Thanks for the replies. I ordered Amsoils' 80w90 synthetic this afternoon.

 

[AuroraGirl]

Thanks for the replies. I ordered Amsoils' 80w90 synthetic this afternoon.

thats a lot of fluid, but its a lot of good fluid! Make sure you got a good new breather and tube

and if yoiu are going big or go home, id put a cover with a drain and fill plug