OK, so in doing my 30,000 mile oil change I went out in search of the perfect Gear Oil, for my usage. I realize that everyone has different preferances, and that people are using all kinds of different oils. So here is my question:

Per the manual on my truck, I should be using a 75w90 Synthetic Limited Slip oil meeting GL-5 requirements. With that in mind I have found the following:

A Chevron 75w90 that does not say it is GL-5 compliant (because it comes in a 5 gallon generic pail), but I am told it is. I asked about the Limited Slip and was told that it wasn't.

I found a gear oil (don't remember the name), it was an 80w140, it was GL-5 certified, but it didn't say Limited Slip. It is rated for larger trucks and 500,000 miles changes. The guy at the Kenworth service center I found this at, steered me away saying I should be buying Mopar stuff from the dealer.

So, what is the Limited Slip? Will I see it on the label? Does it really matter?

I am still reading through all the posts that have been made regarding Diff. Fluid, and hoping to find an answer to this, but if you can help shed some light on this, please do.

 

I thought the type of limited slip device that the HD trucks used did NOT require a LS additive. And typically that's all it is, you buy gear oil, and you buy a small bottle of LS additive.

I'd be sure to get a *GL-5* rated 75W90. There was mention on this forum somewhere that someone had a quieter rear end when they switched from 80W140 to 75W90. The Chevron might be a good call, but I'd be 100% sure it's GL-5. And FWIW I can't find any mention of gear oil on their web site.

FWIW, Mobil1 75W90 meets these requirements and is often found at my local auto parts stores. There are others I'm sure. Verify that you don't need the LS additive, I'm 95% sure, and you should be all set.

 

No LS additive is needed. I believe it states that in the owners manual. I used the Mobil 1 75W90.

 

You are correct in that the manual does say that an additive is not required, nor even recommended. But it does state that the oil should be a "Limited Slip". Can someone else check their manual? Maybe I am reading it wrong.

 

My LS seems to work better with the Mobil and time. After a few days on the road, the LS seems like it was not working at all. Now I can romp on it with one tire in dirt and one on pavement and I get equal spin.

 

From the '03 Service Manual:

 

So is it ok to use the 75w/90 Front and rear on the hd 4x4?
Jon

 

Yes use 75w-90 on both the front and rear. Make sure itis GL-5 & synthetic. Royal Purple, AMSOIL & few other companies make great lubes just for this.
Good luck and DO NOT add anything NO limited slip additives are required.

I prefer the AMSOIL and don't have to change it for atleast 2x to 3x the normal interval