Can anyone tell me where the vacuum reservoir is located on a 01 F150 4x4? I'm troubleshooting the 4wd not engaging want to check the reservoir. Any help would be appreciated

 

Between the battery and the inner fender.

 

....or INSIDE the fender.

Follow the hose....

 

Behind the battery.

 

Thanks everyone - I saw the line tucked behind the battery tray but couldn't see a reservoir. I''ll check again when it stops snowing !

 

IIRC, the reservoir is only about an inch thick,
and clips to the back side of the battery box.

 

So I finally had an opportunity to get into the 4wd issue of not engaging again. I found the vacuum linkage (shaft with notch that moves the differential fork) and the differential fork separated. I pulled the vacuum arm out and reconnected them. The arm that engages the differential is a little sloppy and can move front to back causing the linkage to separate. I see a pin sticking out of both ends where the differential fork is mounted. Is there a way to tighten that arm? That pin is hollow. I thought it was an allen but it doesn't seem to be. Any suggestions??

Edit - Adding picture