limited slip not working?

[jdSVT]

i just picked up an 05 fx4 reg cab, the axle code is 4N which apparently is the 4.10s with limited slip, i don't think it has 4.10 cuz theres no low end torque and only one wheels spins! any ideas

[PGreenSVT]

It's easy to confirm. Jack the back of the truck up and have someone turn a wheel exactly 1 revolution while you count how many revolutions the driveshaft makes. A little over 4 is a 4.10, 3 3/4 is a 3.73, etc.

As for the limited slip, it is clutch activated and the clutches wear out. They are rebuildable. It's a smelly job but not particularly difficult. Pull the axles, pull the diff being sure to keep the caps and shims together for each side. On a bench rotate the spider gears out, take the clutches and steels out and replace with new clutches and steels, rotate the spiders back in, replace the diff in the housing and put the axles back. Put fresh gear oil with friction modifier in and Voila! No more 1 wheel peel.

[jdSVT]

Originally Posted by PGreenSVT

It's easy to confirm. Jack the back of the truck up and have someone turn a wheel exactly 1 revolution while you count how many revolutions the driveshaft makes. A little over 4 is a 4.10, 3 3/4 is a 3.73, etc.

As for the limited slip, it is clutch activated and the clutches wear out. They are rebuildable. It's a smelly job but not particularly difficult. Pull the axles, pull the diff being sure to keep the caps and shims together for each side. On a bench rotate the spider gears out, take the clutches and steels out and replace with new clutches and steels, rotate the spiders back in, replace the diff in the housing and put the axles back. Put fresh gear oil with friction modifier in and Voila! No more 1 wheel peel.

THANKS! il def try lifting the back up to check, as for the rebuild for the LS i think il bring that to someone who knows what there doing lol. You make it sound so easy.

[Huckleberry]

Sometimes to they can get dirty and not activate properly thats what was wrong with mine when I bought it. I serviced it with some good 75-140 gear oil and added some limited slip additive and within about 2-300 miles was working great and still is, that was 30k ago.

[jdSVT]

thats what i figured they might be dirty or tired, but the trucks only got 43k on it idk

[PGreenSVT]

Originally Posted by jdSVT

THANKS! il def try lifting the back up to check, as for the rebuild for the LS i think il bring that to someone who knows what there doing lol. You make it sound so easy.

It's only scary till you've done it and see how easy it is.

[taylorking]

I would flush it out first. My dad had 320k on his dually before he traded it, and the LS worked fine. So I wouldnt think the clutches are bad unless someone really neglected the truck.

I've heard that Ford calls for too much friction modifier in their diffs, which leads to them failing. IIRC its best to use about 2oz. of modifier

[PGreenSVT]

I have 83k on my 05 and my clutches are shot. It happens. In my opinion they are a maintenance item just like brake pads. Your dad did well getting 320k out of his.

[southern7.3]

I need to drain mine and put some fresh oil in it. Ashamed to say Ive never done it

[taylorking]

Originally Posted by PGreenSVT

I have 83k on my 05 and my clutches are shot. It happens. In my opinion they are a maintenance item just like brake pads. Your dad did well getting 320k out of his.

Was just suggesting he flush it before he spent money on clutch packs

Originally Posted by southern7.3

I need to drain mine and put some fresh oil in it. Ashamed to say Ive never done it

Dont feel bad, I havent either. Sad thing is that I have a Trak-lock diff sitting in the shop floor, along with a gallon of new gear oil.