Ok, I am not having any problems at 42K for now but I want to get this done. I have a 2007 4X4 with 3.92 LSD gears.

I think I know I need the 75W-90 for the front and 75w-140 for the rear but my questions are how much of each for the front and rear? I can just buy extra and take back what I need but would rather not.

And if I go with the Royal Purple do I still need to add in the Mopar LSD addiative? Thought I read somewhere that this is not needed with Royal Purple but want to be sure.

Thanks for the help.

 

It is approx 2.5 litres in each diff if I remember right. i wouldn't spend the extra $$ on Royal purple, get a good synthetic oil and buy the LSD additive. The additive can be bought for about 5 bucks at any auto parts store.

 

Yes, 75W-90 for the front and 75W-140 for the rear. You will need 2 and change for the rear so get 3 bottles of 75W-140. You should only need 2 bottles of 75W-90 for the front. I always get 3 but never use more than 1 and most of #2 in the front.

Royal Purple MaxGear is excellent gear oil. I don't consider it a waste of your money as the ^^^ above seems to feel it is. It is what I always run and it has worked great in all of my vehicles from trucks to muscle cars. RP MaxGear does have the LSD additive already in it. You "shouldn't" need to add any. Sometimes a worn or picky unit will require a little extra be added but I would try it with just the RP 1st to see if you have any chattering or banging. Add it if needed. Most people don't need it.

 

I have the same vehicle: 07 4X4 with a 3.92 LSD. I changed my fluid in both front and rear differentials last spring. The service manual calls for fluid to be added to the bottom of the fill hole on the front and 5/8 inch below the bottom of the fill hole on the rear. The front took a little less than 2 quarts. The rear took exactly 2 quarts of fluid plus the 4 oz. bottle of Mopar friction modifier to get it to the specified level (bought 3 quarts and wound up returning the 3rd). I used Mobil 1 which has a friction modifier just like Royal Purple.

I asked service managers at 2 dealers and they both said to add the friction even with axel fluid that already has the additive. The one service manager said the LSD used in the Ram 1500 is finicky and strongly recommended using the Mopar additive. At less than $7, I figured it couldn’t hurt. This past winter we had a lot of snow in the area I live in and I believe the LSD performed well.

 

I 'am going to change the oil in my front and rear diff. and asked the dealer what weight oil they told me 75-90 in the front and the same for the rear unless the temp is over 95 degree's then 75-140 it never gets over 95 where I live so I guess I'll use 75-90 or do you think I can use the thicker stuff and have no problems?

 

I don't see any advantage to using 75w-90 in the rear as opposed to 75w-140.

First of all, I'd only consider the 75w-90 ONLY if I never towed and never hauled. BUT they both flow approximately the same when cold as the 75W indicates, so there is no advantage to the thinner oil there.

The 75w-140 has almost 60% greater viscosity at operating temperature and lays a thicker film layer over all metal on metal components. This thicker film layer is greater protection from the development of "hot spots" on such components.

You might see about a one quarter of a mile per gallon better fuel economy with the thinner oil (woo-hoo) and a slight increase in RWHP (and I'm meaning like 1 - 3 HP) due to the thinner oil having less resistance, but that's about the only thing I can see in using thinner oil. Track guys use thin synthetic oil for every smidge of gain they can get against the clock, BUT track guys also change the fluids more often than I change my socks.

I don't like the fact that your dealer is recommending the thinner oil in the rear. Makes me think they are saving a $ by only stocking one gear lube purchased in bulk and using it for all gear fluid changes, regardless of how the owner uses his truck. Thinner oil is just NOT a good idea for guys who use their trucks as trucks.

I know it's easier to just go get all 75w-90 so you won't have to mess with two different oils and won't potentially have two partial bottles instead of one, but I'd put the 75w-140 in the rear...

 

Mobile Gear oil has the LSD additives in it all ready. no need to buy extra

 

Do as Hammer suggests and put the correct Dodge specified oils into your diff.

For a Ram 1500.
75w-90 FRONT AXLE ± .03 L (1 oz) C205F 1.66 L (3.5 pts.)
75w-140 in the REAR AXLE ± .03 L (1 oz) 9 1/4 2.32 L (4.9 pts.)***

*** *** With Trac-Lok add 118 ml (4 oz.) of Limited Slip
Additive

However, the 4oz of friction modifier is only a suggestion as some need more to stop clutch chatter in the LSD and some a little less. Strat off by adding the minimum 4oz. If chatter free, your golden, if not.....add a little more till she quietens down.

Thees Dodge lsd's are very quirky so dont give them a chance to bite you back!

As for buying 3 bottles for the rear.........well you wont have to next time you do a fluid change and with them coming up every 15000 miles, you will soon be doing it again and you wont then have to buy that third bottle
Plus with the way things are going up in price litterally from day to day.......by the time you come to use it, you will have saved some $;s lol.
See how you can put a positive spin on just about anything???

Al.

 

Ram 1500's

75w-90 for the front....<2qts

75w-140 for rear...2.45qts

Now, if you want to be cheap and correct at the same time, you put only 2qts in the rear diff and a tube of friction modifier. The tube of modifier will get you close to the fill mark(5/8" below filler hole) and only cost you $6 as compared to the $20 bottle of Synthetic 75w-140. It'll save you $14 or so. The reason you can do this is because there is still oil in the axle tubes and down in the front of the diff, so you really never get it all out. There's gonna be atleast .25qts in there remaining. So, you need not to put that much in but a little less.

I have Mobil 1 LT Synthetic and used 2.25qts of 75w-140 and no modifier. I have towed numerous times and never had one issue with chatter.
I have not done my front yet(only at 9.3kmi)