2nd Gen Non-Engine/Transmission Limited Slip + Synthetic = ?

[Israelson]

Just changed gear oil in my Limited Slip Dana 70. The owners manual states for heavy duty towing use Mopar Systhetic 85-140W it doesn't state if it's OK to use it with a limited slip. Does amybody know if this combination is OK as long as I add the friction modifier. Thanks.

 

[willyslover]

A OK to use synthetic with a LS diff..... before you add friction modifier do a search and read... . many postings on the subject and some very good info for you

 

[Loren]

eisraelson,



I didn't use the Mopar synthetic in my differential, but I did fill it with Amsoil. I did not add the friction modifier.



My differential no longer acts as a limited slip. Apparently the synthetic oil is too slippery and the differential clutches won't hold.



Loren

 

[Dennis Garrett]

In 175k, I've tried regular mineral oil, Amsoil, and Royal Purple in my rear end, and have learned one thing. Even if it says LS addditive is not needed, mine will chater & shudder on tight turns unless I use an additive. I've also learned I cannot use anything but the Mopar stuff. I've tried LubeGurad, Champion, and one other (in a blue & white tube, but can't remember the name), and nothing works for mine except the Mopar stuff, about a bottle & a half. I did learn the hard way, even if you do use synthetics, make sure you change it at the recommended intervals. As the clutches work, the clutch materil that wears off will contaminate the fluid. I went 100k on Amsoil 75-90, and my carrier bearings went out, and the super hard grit suspended in the oil ruined all four wheel bearings, and the four carrier & pinion bearings too. I still use synthetic, because I like the lower rolling resistance, but I won't go more than 50k on a change from now on.

 

[Extreme1]

I installed a limited slip in mine almost a year ago. I filled it with 2 gallons of Amsoil and after a few thousand miles, it started to chatter. I added 1 ounce of the Mopar additive and it stopped after a couple days driving (didn't do the figure 8 thing). They are all different, smoe need more than others.

 

[Lsfarm]

I like some Chatter

I like my LSD to chatter some. Mine gives just one or two little chatters when I pull out onto a road on pavement, and it definetely slips one tire when I'm on dirt roads [90* turn]. I don't find this annoying, rather a confirmation that the LSD is alive and well.



The reason I like it like this is that I know that if I get one wheel on ice, that the truck will pull away without spinning one wheel and burning up the LSD clutches.



So far I have never had the LSD let me down, I always get two tracks from a burn-out.



I'm using Amsoil 75W-90, without any additive.



Greg L The Noise Nazi

 

[Sled Puller]

Originally posted by Loren

eisraelson,



I didn't use the Mopar synthetic in my differential, but I did fill it with Amsoil. I did not add the friction modifier.



My differential no longer acts as a limited slip. Apparently the synthetic oil is too slippery and the differential clutches won't hold.



Loren

After you change your rear diff with ANY lubricant, do several tight figure 8's, to relube the clutches.

Otherwise, you will not have a LS anymore. I have tested this several times.





With the Series 2000 line, try it without any modifier, if it chatters, add a littlebit at a time until it stops.

 

[RKohn]

Valvoline with no modifier

It works for me. No chatter. Oo. Oo.

 

[RustyJC]

I switched from the factory goop to Royal Purple synthetic 85W-140. It works fine with my LS with no supplemental friction additive beyond that which is already blended into the RP.



The LS on my wife's Durango, on the other hand, has chattered mildly on tight corners ever since it was new (24000 miles currently). It's never been bothersome enough to mess with, and I'd prefer to have the LS a little "tight" than "loose". Guess I'll switch it over to RP synthetic 75W-90 one of these days.



Rusty

 

[chuck3]

I filled mine with Amsoil and did have to add some modifier later.

 

[Israelson]

Thanks everybody

All your info has been helpful, although some came all to late as I had followed the service manual recomendation and added 8 oz. of friction modifier with my synthetic and confirmed just today what most of you have shared... It was to much, driving through some very mild snow and ice I found one tire spinning on several ocassions resulting in me having to shift into 4WD. It seemed the LSD was way to loose I plan to change the fluid, start with no friction modifier then slowly add only what is needed to reduce chatter, I like the idea of maybe having just a bit of chatter to confirm it's working. Thanks again. Erik

 

[Gary - K7GLD]

One thing *I* have learned in LS threads like this is, seems like each one is a bit different from the rest - lots of guys toss in some synthetic, and because the LS *doesn't* show any signs of chatter, they ASSUME the synthetic is working GREAT! It probably IS - as a lubricant - but has rendered their LS function absolutely WORTHLESS!



Then, there are the others who do the same thing, and still have good LS action... I've installed Amsoil 75w/140 in mine - no chatter OR additive, and will have to do some testing to see if LS operation has been compromised...

 

[Israelson]

Please let us know your results after further testing.

 

[Sled Puller]

Originally posted by Gary - KJ6Q

lots of guys toss in some synthetic, and because the LS *doesn't* show any signs of chatter, they ASSUME the synthetic is working GREAT! It probably IS - as a lubricant - but has rendered their LS function absolutely WORTHLESS!

If this were the case, (it is not) then Dodge has a heap of explaining to do, because since 1994, they have been recommending synthetic in the rear diff.



Instead of waiting for the above testing, use the seacrh feature and find out how many LS units have been rendered useless by synthetic.

And, to be fair, check how many have been rendered useless from casual fluid (any lube)changes, from guys not following instructions properly.



The only thing that rendered mine useless, was my right foot, and I may have overgrossed my hitch a tad.

 

[Gary - K7GLD]

I don't have to "search" very far - here's ONE, right here in THIS thread!



"My differential no longer acts as a limited slip. Apparently the synthetic oil is too slippery and the differential clutches won't hold.



Loren"



And I have read my share of similar comments in OTHER automotive groups I wander thru as well... Face it, MOST owners are only concerned about - and actually CHECK, for EXCESSIVE grip of clutches/chatter after adding different lubes - and synthetics AREN'T all the same EITHER - so just because ONE operates properly in a given LS differential, doesn't automatically mean they ALL will!



On the other hand, if MOST fellas don't get any chatter after switching lubes, how many do you suppose bother to THEN check to make sure they ARE still getting reasonable LS action?



Please describe the accepted METHOD for making that check...



I'll wait...

 

[Sled Puller]

Originally posted by Sled Puller

After you change your rear diff with *ANY* lubricant, do several tight figure 8's, to relube the clutches.

Otherwise, you will not have a LS anymore. I have tested this several times.





With the Series 2000 line, try it without any modifier, if it chatters, add a little bit at a time until it stops.

I guess *common sense* comes into play here.



Find a nice spot that will slip easy, a little wet grass is fine, add a little power, watch your tires in your mirror, or check your tracks.

If anyone else has a better way to test, I will be glad to listen.

 

[Gary - K7GLD]

"If anyone else has a better way to test, I will be glad to listen. ?



UNH- HUHHhhh!



And THAT is EXACTLY why so FEW even ATTEMPT any sort of "test" for proper LS operation - for MOST of us, there IS nothing but guesswork - testing for too TIGHT is easy - too LOOSE is another animal completely! Exactly how LONG should a patch of rubber on the dry side be in comparison to the slick side - how "slick" is "slick"?



Sure, there IS a spec for proper LS operation, but precious few have te equipment or knowledge to apply it - so most just toss in whatever lube they decide to use - if clutches chatter, they add friction modifier - if they DON'T chatter, they simply cross their fingers and hope all is well...



Me, I'll do it same way you do - it's VERY imperfect and open to flaws and misinterpretation, but the best I have available...



And I'm betting MOST don't even do THAT!

 

[Sled Puller]

Let me sum up the novel from above:



MAYBE, IT IS JUST NOT THAT IMPORTANT!!!!

 

[Gary - K7GLD]

"MAYBE, IT IS JUST NOT THAT IMPORTANT!!!!"





HMMmmm - I buy a truck with a LS differential - I'm so interested in giving it "the BEST", that I put in the synthetic lube - and THEN *DON'T CARE* if it works properly?



Am *I* the only one who sees something WRONG with that picture?

 

[tarussell]

I am in no way taking sides or stiring the pot with this addition to this post.

To the best of my knowledge the approved method of testing diff. clutches is to measure the continous torque reading of one side turning and the other side held stationary. Now what most people miss understand is that they try to measure break away torque and not continous rotating torque. That is why the torque value is some what low for the test. Break away torque is much higher than continous torque. The torque value changes for each diff and the agressiveness ( or lack of )of the clutch pack setting.

HTH , Thomas