Just wondering if all fx4 package f-150's have a limited-slip (posi) rear end? I was just off roading in 2 wheel drive and got stuck. When I looked out my drivers side window to see what the trouble was, I noticed that the rear tire wasn't even spinning. The strange thing is, I heard the other one spinning. I put her in "P" and went to havea look for myself. Sure enough the other wheel had been spinning. I was told that all fx4's have a posi rear end, is this true? If so, is something wrong with my diff? Mine is a 2003 with a 5.4 if this makes any difference. Thanks, Dave K.

 

check with your axle code on the door jam sticker and let us know what it says, i believe they were all limited but check just to make sure. also have you heard any noises from the back that would indicate a problem. im no rear end expert but clutch packs seem to be an issue in these truck if not properly taken care of.

 

Even if your truck has a limited slip, it is normal for one wheel to spin at times, depending on how much traction one wheel has and how little the other one has. When clutches are worn it is more noticeable. If you rebuild the clutch packs, you can always install a larger selective shim so there is more spring pressure on the clutches to help lock them together, or just buy a locker.

 

It's a LIMITED slip, which means both tires will only spin under a light load, like if both tires were in mud. The easiest way to check if you have a LS or not is to get the axle code off your doorjamb sticker..

 

It turns out that all fx4's have a limited slip diff. I took mine to my local Ford tech today and he said more than likely the clutch is worn out. According to him, this does happen, however most people do not notice it. He said if I leave it, it won't do any damage. In 10,000 miles or so I am planning on have my tech change the rear diff fluid, I will have him take a look at it then. The strange thing about this whole thing is that right before I got home after seeing the tech, I hit the gas from a dead stop on semi dry pavement and both lit up. And for anyone out there who may ask, yes I am sure when I was stuck the other day that only one tire was spinning. Thanks, Dave K.

 

This is from a 2002 F-150 Brochure, 03 should be the same. Notice that the Limited Slip is not included, form 97-03 it was always optional.

FX4 Off-Road 4x4 Equipment Group: Includes 17" 5-spoke cast aluminum
wheels (4), unique trim (lower two-tone paint, wheel-lip moldings/
honeycomb center grille/top cap and lower valance/FX4 decal and tape
stripe), Rancho heavy-duty shocks, skid plates (fuel tank, transfer case
and front frame crossmember), 3.55 axle, stainless steel lug nuts

 

Check the doorjam code for your info.

I think (not sure) that the Fx4s had the 3.73 gears but for me my code is 19 (3.55 NON Limited Slip )

My old 97 F150 XL had the H9 (3.55 Limited Slip )

LS should just be ****** stock on a truck no matter what. Good luck.

 

beowulf, Zaairman and racerrf150-2,
I just checked my door and it says: H9. After reading what you guys have posted, I am assuming this is a 3.55 Ls. Now I am convinced that you are right. Thanks for the help as always, Dave K.

 

rkjerue- I am just stating what the tech told me. However, now I am convinced that you are right. I mean, come on, If ford wouldn't advertise that their fx4 had a Ls and it did, they would be crazy. I think the tech was wrong.
Dave K.

 

Axle Codes from the door jam sticker

non-limited slip

X27 – 3:31
X19 – 3:55
X26 – 3:73
X25 – 4:10

limited slip

H9 – 3:55
B6 – 3:73
B5 – 4:10

 

H9 seems to be the most popular axle choice....Everbody I know with a F-150/Expy except for a V-6XL has it.

 

Even when it was brand new, I was parking my truck at work, one wheel was on dry pavement and the other was on an ice patch. The wheel on the ice patch spun and the other stayed motionless. The limited slip rear end has a certain amount of break-away torque before one wheel just spins. If one wheel has no traction and the break-away torque of the wheel with traction is reached, the wheel with no traction starts to spin. Give each wheel equal traction and they will both spin. This is normal opperation.
My truck has 3:73 with limited slip, (came with tow package). Window sticker calls it a "Tough Truck Package"

 

dwsf150,
What do you mean by break-away torque? In the case where I was spinning one wheel, would the other one have started spinning if I waited long enough? Sorry, I am just trying to get to the bottom of this. Thanks, Dave K.

 

No. The problem was that you stepped on it, so all of the power went to the wheel with no traction. If you would have gone easy on it, both wheels would have turned.

 

Now I get it! Rather than just giving it the gas, I should have poured the power on slow and steady. Thanks Zaairman, you have been a great help. Dave K.