Hello, I have a 2000 F150 2WD 4.2 V6 automatic, and I was under my truck a few days ago and saw a hose just hanging, I looked around and it appears to go to the rear axle, about halfway between the dif and the drivers side brakes. It doesn’t seem to go anywhere but you can see on the axle where it was before it broke. My question is what is this hose used for?

 

I believe that's the differential vent tube. It doesn't go anywhere.

 

What purpose does it serve?

 

To keep pressure from building up in the diff when it gets hot.

 

As stated, it's a vent and yes, you need to fix it. Should you have to go thru any high water you'll end up with water in the axle which will kill the bearings and the gears. An expensive repair bill. The hose goes to a high point usually above the fender. It also allows for any condensation to exit the rear axle.

 

Okay so how would I go about fixing it?

 

If it's broken off, cracked, to short, etc, replace it. otherwise, route it as high up under the bead as you can and secure it with zip ties or similar. Adjust the end so the opening points downward (put a half-loop in it).

 

And when you zip tie it, make sure there is enough extra hose for the suspension to drop down as far as it is capable or the hose will be pulled off the diff.