I drive a 2002 F-250 SD 4x4 with a six speed trans and a limited slip rear. As far as payload, the truck performs beatifully. However, the truck is terrible in snow compared to all my previous 4x4s. My neighbor will not let me forget that his chevy blazer had to pull me out of my driveway twice this winter. Part of the problem, I believe is that the limited slip unit is so weak. As soon as one rear wheel has even slightly more traction than the other, only one rear wheel spins. I have taken it back to the dealer five times, and they finally said it's normal. According to the dealer, the engineers at Ford tech assistance line said that the amount of torque required to make the unit slip is only 20 ft/lbs. I can rotate one wheel by hand, with some resistance, with the other on the ground. Can this be right? Is anyone else out there having similar problems?

 

The rear limited slip is a known weak spot in the rear axle of these trucks. Try feathering the brakes when it doesn't seem to work, this "tricks" the unit as if the tires had traction and once the limited slip unit is working it tends to stay working till you stop completely again. Some here have had better luck with a synthetic lube in the pumpkin also. Hope this helps.

 

Here's a slightly modified version of my pat answer on LS questions.
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LIMITED SLIP

Before you tear into your diff., a little explanation of how your limited slip works, I can't remember which site I found the info on, but try some of the popular LS aftermarket companies, Auburn, Detroit, ARB, etc... You'll find lots of useful info there. Also, for a real simple explanation of how your LS works, try www.howthingswork.com.

The LS system in your rear diff is actuated by torque, which in turn causes friction on a clutch pack. If the vehicle is stationary, with one rear wheel (especially a dually) spinning, the wheel rotates so freely that there is insufficient torque to activate the LS. This problem is especially bad in snow and ice. Rememeber, it's not a locker, it's a clutch system.

Essentially, both wheels must be moving forward for the LS to work. At the least, there has to be enough traction at the free spinning wheel to apply sufficent torque to the clutches for the LS to engage.

I had the exact same scenario you described happen to me within a week of buying my truck, and, like you, I was peeved. A little research into the problem, and the folks here, helped me to understand just how my limited slip worked and realize that in fact it was working as it should.

That being said, if you do have higher miles on your truck, the LS may be worn out or not functioning at its best. I would advise starting by changing the fluid in the diff. The concensus is that a good quality synthetic like Mobil 1 will give you the best operation of your LS and the longest life and durability. Remember to add the specified amount of friction modifier.

A common trick is to apply light brake pressure or lightly engage the emergency brake to supply the resistance/torque needed to engage the LS clutch pack.

If you're still not happy, the clutch pack can be rebuilt or it can be replaced with an aftermarket unit such as the Auburn or a locker, the most common being a Detroit.
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Good luck,

Waxy

 

I just went through the same thing this last weekend and Waxy is right on the money.

I too have had the truck in to the dealer to get the LS looked at as I didn't think it was working properly only to be told it was.

This last weekend I found myself on a frozen lake with about 18 inches of snow cover. When the I got stuck in one spot I ended up digging the wheels right down to the ice. Once that happened the LS no longer worked.

I did try the brake trick but to no avail.
Once we made it back to shore and some better traction I noticed the LS was working again and chewing through everything quite nicely.