How does the LS on rear diff work? - Ford Powerstroke Diesel Forum
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post #1 of 13 Old 01-07-2010, 10:51 AM Thread Starter
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How does the LS on rear diff work?

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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post #2 of 13 Old 01-07-2010, 01:55 PM
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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.

Late 99 F250 ext. cab 4x4 Lariat 7.3
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post #3 of 13 Old 01-07-2010, 03:13 PM Thread Starter
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What does it lock up to if both wheels are in the mud ?
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post #4 of 13 Old 01-07-2010, 03:17 PM
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WTF are you talking about? the rear end locks up- both wheels spin.

Late 99 F250 ext. cab 4x4 Lariat 7.3
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post #5 of 13 Old 01-07-2010, 03:18 PM
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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

1997 Single Cab Dually, S366 w/ Irate mount and plenums, EFuel, Intercooler, P.I.S 175/80s, Corbeau seats w 08 console, 19.5s, 6637, Black Interior with swede headliner and visors, Custom badges, Flight Fab Traction Bars.
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post #6 of 13 Old 01-07-2010, 03:22 PM Thread Starter
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Quote:
Originally Posted by robthebuilder View Post
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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post #7 of 13 Old 01-07-2010, 04:14 PM
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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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post #8 of 13 Old 01-07-2010, 04:21 PM
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sorry, geez, get a sense of humor.

Late 99 F250 ext. cab 4x4 Lariat 7.3
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post #9 of 13 Old 01-07-2010, 04:24 PM
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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.

2003 F250 CCSB, straight piped
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post #10 of 13 Old 01-07-2010, 04:50 PM
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HowStuffWorks "Clutch-type Limited Slip Differential" check this out. the fords use a conical spring under each clutch pack instead of one in the middle, but same concept.

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