Limited Slip Differentials -- questions?

[Runaway]

Getting ready for my trip west and changed fluid in rear differential to MOPAR 75W140 synthetic. Since it is a L/S Differential I added friction modifier. Bottle says to add 2 - 5% of weight. I'm assuming this means the weight/vicosity of the fluid. This means somewhere between 2. 8 oz up to 7 oz of modifier would be needed. I added about 3 oz and then took it for a 10 mile ride really mixing up the fluid - hotrodding! If I were to hear any noise because of not enough modifier, what would I hear or feel? I didn't notice any new noises or feel any new vibrations.



2nd question, I am planning on changing the fluid in the front differential this weekend to a 75W90 synthetic. Was thinking Mobil 1 Synthetic. Pros or Cons? Would be interested.



Why heavier in the rear you ask, my faulty logic says thats where the main stress will be from towing and thats what DC recommends.



Thanks for knowledge.

 

[John Berger]

Figure eights are what the doctor ordered

Hot rodding it probably won't get the job done. Take it to a big enough parking lot and do 8-10 tight figure eights and call me in the morning.

 

[Texas Diesel]

John Berger is exactly right, I think 8-10 figure 8's is what DC calls for. If you dont have enough modifier you will hear the inside tire skipping during tight turns. You can over do the friction modifier, most people that use synthetics dont add any friction modifier at first but only add it 1 or 2 oz at a time if it does lock up prematurely. Start with 1-2 oz's, do the figure 8's to work it in to the clutches then try a turn then add more if necessary. Synthetic is slippery enough you may not need any at all.

 

[Runaway]

Figure 8's

Forgot to mention that I did the figure 8's also. No noise, lock-up, etc.

 

[Ramafid]

I have mobil 1 synthetic in the front and rear diffs. I added one bottle of the friction modifier and had all kinds of chatter. I then added the second bottle and smooth as can be. My LSD works very well in all conditions. Guess it's trial and error for each truck.

 

[WOWZY]

I had posted a few weeks ago about wondering if DC actually put the LS unit in mine, the way it was really hard to get both tires to spin.



I pulled the cover off (Damn, did they use JB Weld as silicone?!) and found that there was a LS unit in there. I used Kendal LS gear oil in mine and it performs perfectly.



Does DC put too much LS additive in for a reason? Is it to keep the Mighty Cummins from ripping a virgin Dana 80 to shreds?

 

[HC]

I'm using the lighter Amsoil gear lube up front, the 90W-140 in the rear. Since I rarely tow anything, I'm thinking I'll go lighter in the rear on my next change. Prior to going to Amsoil, Mobil 1 gear lube was my choice - I don't think you'll go wrong with either one.

 

[Runaway]

Front Differential maynot be L/S!

Thanks guys for the replies, one last question, the rear differential definetly is L/S. The front differential I am wondering if it is or not. The insides looked just like my "99" did and that truck didn't have LS. Curious?

 

[Texas Diesel]

Front diff is not L/S because of the "center axle disconnect" design.