my question is I have a 3.55 and it has a limited slip do i have to add the slip fluid to the rear diff fluid when i change it. what would happen if i didn't.

 

Yes, the 4 oz. additive works as a friction modifier with LSD rear ends.

 

I think you'll get chatter (won't slip enough) if you don't put in the additive. You'll notice it when turning. You probably are putting excessive strain on things if you don't put in the additive.

 

if you use the Lucas synthetic fluid, they claim it already has it added. can anyone confirm this?

 

Are you sure you have a limited slip diff? In 2010 LSD came only on the 3.92 and 4.10 axles. Don't know for sure about 2009s but I don't think it was different.

Rob

 

If it chatters, add the additive, if it does not, no additive is usually needed. Only add 2ozs at a time until chatter is completely gone, THEN just add an extra 1/2 ounce when done. Some of these gear lubes that say they have the additive already in it, i have always found that sometimes its not enough for some LSD diff`s.

 

thx Lu, tackling this project soon.

 

Did you have a limited slip differential added to the truck after you bought it? Are you sure you have 3.55 gears? For 2009 models, all 3.55s had an open differential, and all 3.92s had a limited slip.

 

my build sheet (2009) shows:
3.55 rear axle ratio
corporate 9.5 LD rear axle
Conventional Differential Rear Axle
so, no LSD on mine? Then no friction modifier needed?

 

You have the same as mine, open diff. No additive needed.