What is this hose under my truck bed?

[JM in KY]

What is this? Or maybe what did it used to be?

I was under my truck making sure the spare tire was inflated and I noticed this hose hanging down from the center of the bed. It’s capped at one end and looks to be cut off at the other. Not attached to anything, but held in place by a very stock-looking bracket. Under the dirt, the bracket is painted the same color as the truck. Pictures are after I removed the hose, but I left the bracket in place.

 

[nvrenuf]

Axle vent tube. Look for a nipple on the axle housing.

 

[RecklessWOT]

^exactly this.

That "cap" on the end is actually a one way valve, prevents water from getting in while still allowing the axle to vent.

If there's no vent attached to your axle and the nipple is wide open like the tube just fell off then you run the risk of getting water in there from normal use like driving in the rain. If someone capped it off that's bad too, you would build pressure as the fluid warms up while driving and you'd end up with a leak, more than likely your pinion seal.