I have an 04 1500 with LSD. The owner's manual recommends Mopar Synthetic 75W140 and 4oz of additive for the LSD.

But I see a lot of you run Royal Purple 75W90. Which should I use and how much of it do I need? I just got back from Autozone and they only had Mobil 1 synthetic 75W90 in stock. I do a lot of towing, which do you experts recommend?


Thanks for your input.

- Fris

 

75w-140 most definately if you tow! 75w-90 is like $12 and 75w-140 is almost $20

 

OK thanks I will go with the 75W140. I am going to use the Mobil 1 Synthetic. Do I still have to use the LSD additive? Because the Mobil 1 says it is good for limited slip diffs as well as conventional.

 

I've had good success since new in 2005 LSD running RP 75W140 'without' the additive although I bought a bottle from the dealer before I read the fine-print from RP. It probably won't hurt to use the additive however I vaguely remember in a few posts from long ago that it did cause some minor problems by using the additive - but now I don't recall what they said happened.

 

Mobil 1 does have the LT labeled diff fluid which does have some additive in it. Me personally, I added the additive even with the Mobil 1 fluid.
Worse case scenerio on not adding it, you get chatter going around a turn and then you'll have to pop off the rubber cap and add a few oz. not a big deal really.
If the Mobil Bottle says LT, you should be fine. it's up to you I suppose. Lots of guys use RP with no additive. The newer Mobil should be the same.

 

ok thanks, thats what I will do. I gotta replace the pinion seal at the same time.

 

Just make sure you torque the crush collar nut at the desired specs for a "used" collar and bearings. Cannot overtighten that or you will cause problems with your pinion backlash

Pretty sure it's 10-15 for used and 15-20ft.lbs new....double check that. I posted up the other day the specs. i'll see if i can find them again