I just purchased a 1991 F-150 XLT Lariat with the 5.0 efi. Truck is in really good shape and the four wheel drive has auto-locking hubs, a feature that I haven't had before. It's pretty handy. now I have two questions.

1. Although its in great shape, It's obvious to me the some of the vacuum lines are either connected incorrectly, or capped off/terminated when they shouldn't be. Does anyone have the vacuum diagram for this motor? every one I have found shows one vacuum port on the passenger side of the throttle body between the cold air intake hose ports. This one, however, has TWO vacuum ports on the DRIVER side of the throttle body instead. These two ports are simply terminated to each other. There is a vapor can in the front driver side fender, where a second battery would be on a diesel. One of the two lines on this can is broken off with an inch stub left behind.

2. When I purchased the truck, the previous owner warned me that it needed a new driver front rotor and that in order to save gas he had removed the front drive shaft. Luckily i was able to take the drive shaft off of my 84 instead of buying one. Now when I engage the four wheel drive, sometimes it works perfectly, other times it begins loudly clanging. I stop completely, put the transmission in neutral, shift the transfer case back to two wheel drive, then back to four, then put the transmission back in drive or reverse. This has resolved the problem MOST of the time.
On another occasion, when I was done using the four wheel drive, I put the transfer case from 4H to 2H for regular on road driving. there was a light metallic grinding/slipping noise. I stopped completely, reversed for a few feet, then tried forward again, and all was fine, noise was gone.
Is this a sign that the hub needs replacing? the noise does seem to come from that front driver hub.

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