Warning an automotive novice asking question. 1987 F150 5.0 with 4WD. My wife noticed something dangling under the truck when she was following me yesterday. I crawled under and saw that is was a rubber line near the rear axle that had separated. There was a nipple with a small portion of the same line on the drivers side of the axle. I reattached it but I am curious as to what it is and what it's function is. The transmission has been suspect for a while and had just started occasionally slipping. Thanks for any help you can offer.

 

It's not transmission related , On the driver's side of the rear axle should be a threaded nipple that also holds the brake line secure but it is also the axle housing vent and should have a rubber tube connected to it that the other end is secured to the under side of the bed or frame rail above the axle itself . The oil / lube in the rearend just like most other liquids when heated (from driving) the left sitting to cool will build or accumulate condensation inside the axle housing , once heated again (from driving) it will need a way to vent off the condensation and any gasses from the heated oil , CHECK that nipple to make sure it is not clogged otherwise you may end up blowing out an axle seal from the pressure building up with no way to vent it .

 

Just the information I needed. Thank you for sharing.