What gear oil weight for 9 inch

[kobyfresh]

Have a freshly built 9 inch with 4.11 posi. Wasn't sure of proper gear oil weight to add, and any brand recommendations. Also, even if they say their good for limited slip, do I still need an additive. Thanks

 

[bax]

Yes on the additive and 90# on the oil. Additive if you have a clutch pack style "limited slip"

 

[kobyfresh]

Yeah, it's the clutch pack style. Thanks for the input.

 

[Broncobowsher]

Some oils already have the additive, if so it will state so on the bottle.
Brand, what ever floats your boat. I can't think of how many 9" axles I have seen with 300, 400k miles on them and still filled with what ever came out of the factory. and it sure wasn't anything fancy. The lubricating requirements are not very demanding in most applications. Being Ohio, I would look for a 75W90 oil. That will be thin enough to flow good on those cold winter mornings. I save the 140W for tow vehicles in Arizona where the oil gets super hot, then I go synthetic as well due to the heat.
Fill to the bottom of the fill hole.

 

[bax]

It's a new set up so yes on the additive.

 

[blubuckaroo]

My gear guy said any brand but Sta-Lube.

 

[BwoncoHowie]

Have a freshly built 9 inch with 4.11 posi. Wasn't sure of proper gear oil weight to add, and any brand recommendations. Also, even if they say their good for limited slip, do I still need an additive. Thanks

I concur with Broncobowsher.
Just because a certain oil is recommended for use in limited slip applications doesnt mean it contains the needed additive, which is a friction modifier.
If your diff has clutches, dont forget the BSS (Blue Stinky Stuff) It's Ford traction-lock liquid additive in a small plastic bottle sold in Ford motorsport packaging.

Make sure the oil is approved for Hypoid. Valvoline, Castrol, or Chevron on the brands. Valvoline makes a good 75-90W .