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Old 01-24-2011, 10:21 PM   #1
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Default Limited Slip ?

I just bought a 1998 2WD F150. Love the truck, but wish I had held out for a 4WD.

The reason is that I could use the extra traction at my hunting land. Not going off road, but some areas get real muddy.

Anyway - just wondering if it would be worth the money to upgrade the differential to a Limited Slip.

Again, just want some extra traction on muddy areas with my 2WD.

Do they even make an aftermarket LS for a 2WD?!?
How much would it run?
Worth it?
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Old 01-24-2011, 10:39 PM   #2
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this may not be what your looking for, but i have a 2wd also, and i can get a positrac for $70 bucks for mine (not installed in the rearend)
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Old 01-25-2011, 12:54 AM   #3
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Quote:
Originally Posted by 2wd5spd View Post
this may not be what your looking for, but i have a 2wd also, and i can get a positrac for $70 bucks for mine (not installed in the rearend)
Cool.
Know anyone who has it?
How much installed?

How would it affect tires / mileage / other stuff?
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Old 01-25-2011, 08:19 AM   #4
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I do not know any of those. But would like to! Gettin tired of the 1 wheel burnouts!
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Old 01-25-2011, 11:40 AM   #5
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Just get a lock-rite locker
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Old 01-25-2011, 04:44 PM   #6
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doesnt effect tires mileage or anythign. posi trac and limited slip are the same thing. sends the power to the tire with the most traction
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Old 01-25-2011, 05:42 PM   #7
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FYI - looked at the door code - 9H
So it's a 9" LS

So with a stock limited slip, what can I expect?
Worth buying a locker or similar product?
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Old 01-25-2011, 06:36 PM   #8
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limited slip id say would be pretty good. mines a open diff and theres many times i wish i had LS
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Old 01-25-2011, 11:06 PM   #9
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Quote:
Originally Posted by AYBABTU View Post
FYI - looked at the door code - 9H
So it's a 9" LS

So with a stock limited slip, what can I expect?
Worth buying a locker or similar product?
Depends on how worn the limit slip is, but even new they aren't perfect.

Some clarifications:

H9 axle code is the same as mine, it means 3.55 ration limited slip. It doesn't say anything about which axle housing it is. If it has the 5.4L like mine, its the 9.75" housing. V6 and some 4.6L are 8.8. Ford hasn't put 9" rear ends into new vehicles for quite some time.

Limited slip differentials (posi-trak being the GM brand name for it) don't send power to the wheel with the most traction like someone said above. The factory limited slip works by using spring pressure and clutch packs to establish a minimum torque threshold between the rear tires before it will let one tire spin relative to the other. If both tires are on similar traction surfaces, both will spin if pushed past the limit of adhesion (this is how you get nice two wheel burn outs). If one side is on a slick surface (ice) and the other is grippy (asphalt) and this traction difference causes a high enough torque difference, the wheel on the slick surface with the least traction will spin by itself. While this is happening, you are rapidly wearing out the clutch packs in the differential, so don't keep your foot planted, let off and try agian with less loud pedal.

Limited slips, like all differentials (excluding spools), have to allow the rear wheels to rotate at different speeds when turning corners. If they don't, one tire will hop and screetch around the corner while causing driveline bind on pavement. The spring pressure and clutch type determine the torque threshold mentioned above and how easily the truck turns corners. Because the factory designs the truck to be driven mostly on the street, so this threshold is realtively low. This means off-road where you are likely to encounter different traction side to side on the truck the factory limited slip will give up and let one wheel spin fairly easily, but no where near as easily as the "zero" torque difference of an open differential. Aftermarket LSDs use stronger springs and "grippier" clutches to raise the torque threshold and provide better off road performance at the possible expense of increased turning effort.

This is different then lockers which physically lock the rear wheels together. Automatic lockers (like the detroit true track) use some mechanism to sense the torque difference between the wheels, unlock at the appropriate threshold and allow differential action, such as when going around a corner. The Detroit Locker uses a "ratchet" mechanism with a spring and ramped locking teeth for this. Selectable lockers (like the ARB air locker) operate in the opposite way. They remain unlocked and act like an open differential until the driver locks them in. At this point both wheels turn at the same speed and are given the same torque, just like a spool. Spools are always locked and always send the same torque to each wheel but won't let them rotate at different speeds. They are for off-road or drag strip use only.

Notice none of these systems can "sense" which tire has more traction and send it more torque. For that you either need an electronic, ABS driven traction control system which brakes the spinning tire, forcing torque over to the other one, or possibly a torsen gear style differential. Don't ask me how those work, its been a while sense I studied them.

For your situation, go slow and if you notice you are lighting up one wheel a lot, consider switching to an after market LSD.
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Old 01-25-2011, 11:28 PM   #10
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welcome to 2wd haha. get a good set of tires and dont stop in the middle of mud... try to go into it at a little higher rate of speed, but nothing too crazy. You just need momentum, thats pretty much how ive done it with my truck for 6 years. As for the limited slip, if you have an H9 axel code like me then it has an LS with it. Im not to sure about how well yours it working by this point, but im pretty sure mine is probably shot by now and I have a '99
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