Hey guys, i have 99 F150 that is 2wd. The code on the door says that i have a LS rear end. A buddy of mind told me that a LS and a posi are 2 different things. I told him he is full of sh*t. Is he right and im the one thats full of it? I just always thought that they were the same thing. Thanks for the info.

 

LS is ford and POSI is chevy LOL same difference

 

Man had this been beat to death... I'm not even getting involved lol.

 

"Limited Slip" is a generic term - not specific to Ford. "PosiTraction" is a name GM used for their limited slip diff years ago, but now Eaton owns that name. Eaton also bought TracTech which owns the Detroit line of diffs. Eaton's LS is the TracLok, which is what Ford has always used. Read this post & the links in it for more info.

 

Well...

I have always considered "Limited Slip" and "Posi" to be generic terms.
In my experience (Atco Drag/4X4 Trail/Bloomsberg/Engine Shops)

Limited Slip is **OFTEN** used to indicate or mean a 'clutch based' dif.

Posi is **OFTEN** used to indicate or mean 'gear based' differential.

But really... they are interchangable...

I would say... when referring to a rear differential and its capabilities, refer to the specific technology or brand used ro create "posi tive traction"

 

alright thanks guys. it sounds like just a brand name issue more than a technical issue.

 

"PosiTraction" is a corporate-owned trademark, which is pretty much the opposite of a "generic name". And it's a clutch-style LSD. "Limited slip" is an industry term for several styles of mechanism that have friction materials in the diff carrier that tend to make the axles turn together. Gear "LSD"s are actually "torque-biasing", which is a totally different concept from LS. They have no friction materials, and work on a different principal.

 

Gear driven torque bias units are similar to the torsen diffs. that go into ATV's right Steve?

 

Indeed.... Torque Biasing units fall into the limited slip category in my brain anyways because, well, that's what they do: They limit the slip ratio of the slipping wheel. But that's splitting hairs....

100% correct! The Detroit (Eaton) TruTrac, Torsen Limited Slip, and Quaife units are all gear-based torque-biasing differentials. I've had a Torsen unit in pieces in my hands, and I still don't understand how the doggone things work! I just know they out-perform any clutch-based unit by a million miles!

-Joe

 

The Zexel TorSen (Torqe-Sensing) was one of the first torque-biasing diffs, and probably still the most widely-used (as OE). Their website (linked in the post I linked above) explains how it works. It's really a very elegant design. The transverse helical gears inside it exert a side force against the case when a wheel slips, causing a gradual & proportional change in the braking force applied to that wheel.

Limited slips use springs that apply a nearly-constant braking force at all times, regardless of wheel slip. That's why torque-biasing is different. Another famous one is the GM Gov-Loc, but it's famous for exploding when overrevved. Too many tiny parts.

 

Giddy-up 409, my 4-speed,dual quad,posi-traction 409! Beach Boy's 1963!

 

My formula team uses a torsen style diff. because that sucker can take a beating, it has around 85-90 hp. going through it in corners with lateral G-loads of 2.3 peak and well above 1.5 sustained. I didn't really understand much about how they work till I read your link, but those diffs are amazing. We have gone through many motors, many clutches and a trans, but still the original diff. with a custom aluminum housing to replace the heavy steel one.

Thanks for the good links, it's always nice to learn something new