I'm getting ready to change my diff and transfer case fluids over to synthetic so I have been reading as many threads as I can with people's opinions on what type of fluids and whether a friction modifier is necessary or not. Which brings me to my question... I don't think my truck has a LSD and that surprises me. (Dana 70 rear) I even pulled out my original window sticker and it makes no mention anywhere of a LSD. How do I confirm that this is correct? Is there a code in the VIN? A tell-tale difference in the diff? I want to use a friction modifier if I have a LSD, but don't want to waste my time if I don't.

 

I refilled mine with Amsoil synthetic on my last change.
Mine has the LSD.
No modifier needed.



Ed

 

You should have a bolt tag on the diff telling you if its LSD or not, all mine have came with this tag...........Pete

 

The diff should be tagged and in the glove box there should be a sticker that has a few build codes on it telling you things like diff gears, limited slip, type of diff, transfer case, ect. I put valvoline 80-90w with two bottles of additive (in a Dana 80) and I can pull my TT trailer then put my hand right on the cover. Pretty warm but not to hot to keep my hand on it. I wasnt sold on how well synthetic works with a LSD and mine works great with non-synthetic. Personal preference.

 

If you jack up the rear end and spin a tire the other will go in the same direction if it's a lsd.

 

Thats the idea but it may not spin at the same speed since LSD's work on applied torque. It definately will not spin the other way like an open differential.

 

[quote author=Gary - KJ6Q link=board=4;threadid=17909;start=0#msg167615 date=1059923853]
[quote author=Shovelhead link=board=4;threadid=17909;start=#msg167605 date=1059919512]
I refilled mine with Amsoil synthetic on my last change.
Mine has the LSD.
No modifier needed.

Ed
[/quote]

The modifier, with synthetics is RARELY the issue - what IS the issue, is whether or not the limited-slip function still works or not - many don't with synthetics, and owners blithely ASSUME all is well just because they don't get any differential "chattering", until they get into a situation where the LSD is actually needed, then it's

surprise surprise surprise.....

Try putting ONE rear wheel on a stretch of slippery surface, the other on a solid and dry surface, and try a moderately quick takeoff - THEN get back to us on how well the synthetic and your LSD is working - the fact it doesn't chatter is only HALF the story... ;D ;D
[/quote]

Real world experience over the years. Works well for me w/ no loss of traction in my clutch type diffs. Nor, of course in my Detroits, or in my spooled Jeeps.
To each, their own.
Verify your own performance, as I do mine.
Use the proper fluid for your application.

 

FYI--

ALL VALVOLINE gear oil products sold in 1-qt bottles already have the modifier in them. no matter whether its dino, syn, blend or whatever. Applies to ALL viscosities.

I went though this debacle in figured it out after calling valvoline.

Justin

 

What if the LSD doesnt work for some reason? Like if the clutches are burnt out. Will both wheels still turn the same direction then?

 

If the clutches are used up, it will acts like an open diff. If you jack up one wheel, it will turn freely or easily with the other on the ground.

JLH