Hi fella's, I have an 04 FX4, with a 3.73 L/S rear diff. The code on the drivers door pillar is B6. I have owned several trucks with L/S rear diffs and have always been able to feel them working in tight turns especially on wet pavement. Can't feel this one at all. Is that unusual. My last F-150 was a 99. Has something changed since then that I'm not aware. The truck only has 30K on it so the fluid shouldn't need to be changed. Whats up?? Thanks

 

I've never really noticed mine until I'm off road and need it. I even had an open diff and when I blew that I replaced it with a Ford LS, but still never felt a difference. Perhaps a really good setup with just the right amount of friction modifier will eliminate chatter. The only time I notice it is when I make a <i>hard</i> right turn and stomp on the gas, not just turning normally like other people report. I was curious about this myself. Here's a simple test: stop in some dirt and power-brake it a little. Pull forward and look at your ruts. If there's two, it's probably working. If there's one, you may want to have it looked at. The factory Ford LS is not very good though, and having only one tire spin is not uncommon.

You can also jack the rear end off the ground and put the truck in neutral. Spin one of the tires by hand. If the other tire turns inthe same direction, your limited slip is most likely working fine. If it turns the opposite direction then either you don't actually have LS, or your clutches may be worn out. Somebody please correct me if I'm wrong about any of this.

 

You probably have LS, These LS suck. Fords LS in the 8.8 and the 9.75 are horrible. Ive swapped them out in every Mustang, LSC, Thunderbird, and now my 05 F-150 They are all junk. By the way I have the 3.73s and LS also with 11k. In the 8.8 I always had great luck with Auburn and Eaton. I Havent researched the 9.75 yet. Good luck.

 

What is it about the LS in these axles that suck? I had an open diff in my Ranger and had a ton of trouble driving through snow in 2wd...half of my driveway doesn't get sun because of my house and it's pretty steep, so the snow doesn't melt. The first day I got my fx4, I left that morning in my Ranger, and had to put it in 4wd. When I pulled back in and back out in my f150, I went up it no problem in just 2wd.

I also was trying to get over a lane the other day right when a light turned green so I gave it a good bit of gas and both rear tires spun. I think it is a great axle, but I only have 200 miles on mine...do they stop working after only a few thousand miles or something? I noticed they call for a special fluid in the owner's manual, maybe someone changed yours and put the wrong fluid in.

oh...and other than that, I have no idea I have a limited slip...it doesn't act up at all like my old Dodge Dakota used to. That thing would drag a tire around every turn under 10 miles per hour.

 

I change my own diff fluid and I'm positive I put the limited slip additive in. My rearend will spin both rear tires about 3 out of 4 times. That's not a very good ratio.

 

They are only able to transmit a small percentage of torque from side-to-side.

Some mechanical LSDs can transmit upwards of 50% of torque.

 

so let me get this straight .. it doesn't always work ... cause when I have alot of articulation (like today one tire was in sand and one on very hard dirt) it would not spin one with good traction. but when I am in question I put my nose in a gravel pile and both will turn... is this normal or is something wrong..??

 

Sounds about right to me. Crappy...