Well I got rid of my auto hubs a long time ago, right after I figured out that the vacumn was part of the reason the unit bearings go out. after replacing my bearings then about 10,000 miles later having to take one side apart to replace the ball joint I found a LOT of grease sucked out of that new bearing. disconnected and plugged the vac line and 30k miles later guess what all the grease is still in teh "sealed" bearing and not spread throughout the hub itself and no more issues wiht bearings going out.
So I installed a set of Warn lockouts and viola no more problems with my front end.

 

was just wondering,but the manual says to keep it under 45mph.

 

Keep what under 45? If you are trying to shift into 4wd High, then yes you must be driving less than 45 mph (according to Ford). Otherwise, it won't even attempt to shift into 4x4. However, I've tried turning the **** at about 40 mph once, and the hubs slamming locked at that speed sounded horrible. I'll never do that again. It's 5 mph or less for me.

Also it won't shift out of 4wd until you're under 50 mph. At least on my truck it will shift out at 49 mph. Some others might vary a bit.

 

What i was trying to say is if your doing the 1/4 mile and finish at 80-100mph is it safe for the front end by going over 45mph?

 

Oh yeah. You can do that all day long. Just don't try turning