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Discussion Starter #1
I just replace differential oil and added the LS additive. I do not see any difference in performance and am wondering how this feature works? Does it help get the truck out of mud hole (mine is 2WD) ?
 

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When I was out slipping around in the snow today, I noticed the wheel had to spin quite a bit before the rear end would lock up. But I felt it lock up and off I went. I'm not sure if it should take that long to engage or not.
 

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When i changed my oil i didnt add the additive. They owners manual didnt mention it. IDK if it matters or not but mine is 4x4
 

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Discussion Starter #6
WTF are you talking about? the rear end locks up- both wheels spin.
No need to be nasty, Rob. I do not understand how the mechanism work and locking up means and thus the question. I'd appreciate an intelligent reply, if you can/want....otherwise, please leave the profanity out of this forum.
Thank you
 

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OK, I'm not sure how to explain this but I'll try ;)

So you know that when you're in a turn, the outside tire travels more distance (in feet) than the inside - right?

That means there has to exist some way of compensating for this. A "spool" which DIRECTLY connects the ring gear with the axles, and has NO compensation, will squeal & slide the tires when turning.

In a regular diff this is simply done with a set of smaller gears (called spider) that are between the Ring & Axle in the "open" center of, what would be, the spool.

In an LS diff there are "frictions" (disks with brake-like linings as in an automatic trans) that keep the spiders from engaging easily so you can turn without trouble BUT if one axle unloads, instead allowing ALL the power to go to that axle through the spiders, it forces them to work against the frictions there by forcing power to the "loaded" wheel also.

The "Friction Modifier" prevents the clutches (frictions) from burning-up when they slip. Ford uses WAY TOO much of it for the LS to work well

I don't know how clear this is.... ;)
 

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On my last truck(f150) if I didn't use the friction modifier additive the rear end would make noises around sharp turns. Put the additive in and it was quiet again.
 

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Discussion Starter #11
Guys, thanks for the explanation. I've been driving sedans for the past 36 years and have not heard about limited slip diff. This is the first truck for me and am learning something new everyday with it....:)

Is it true that with the Purple Power diff oil there is no need to add friction modifier? The shop which changed oil said Purple Power would help significantly to get the truck out of mud hole if I get into one. I was clueless to judge one way or the other, so I told them to use standard oil (75W-140) and add friction modifier as specified by Ford. So far I note no difference before and after the oil change and have no idea if too much or too little modifier was added.
 

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If the "Ford Recommended" amount of modifier was added, you've got too much for the LS to really work as it should.

ALL manufactures add too much for a couple of reasons...

Lots of modifier ensures that the frictions make it through the warranty period :) AND it eliminates complaints from customers who might complain of, occasional, "chatter" noise coming from clutches that stick slightly in a tight turn (I like hearing a little chatter now and then in a tight turn, it lets me know that stuffs working back there ;) )

The long tested method has been for Many years, in cars & trucks alike, to add just a little bit of modifier when you change the fluid. Then, in a parking lot with clean dry pavement, turn as tightly as you can to hear the clutches chatter and add a bit more modifier, a little at a time until it just goes away.

This ensures your frictions are protected from early failure AND lock-up, as best they can, when you need them to.

Another consideration might be though, that now that these trucks have lots of mileage on them, your clutches could be pretty worn by now and not be able to be brought back to working as well as you'd like.
 

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I have a limited slip rear end also. My truck has 156,xxx miles and the fluid has never been changed to my knowledge. ( previous owner kept meticulous records of EVERYTHING). When driving in the snow, the rear end spin both tires from a stop, which means it is working properly. However when i stopped completely with one tire on ice, and then tried to start, only the tire on the ice spun. Would changing the fluid possibly make it grab easier and rotate both tires in a situation like that?
 
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