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Please include the year,make,model,sub-model,engine,2wd,4wd,flex,gas,diesel. Please click accept when done, thank you and come back often. Can you see that the outer cv joint is turning, as seen in this pic, if so then the splines on the hub or halfshaft must be stripped.
Click here for the pic.
On page 170 of your owners manual which I uploaded here http://www.mediafire.com/?j759gafu9hz9k5e
it says the front drivetrain has automatic locking hubs. That is a good question, how they automatically lock up, let me see if I can find a technical answer to that because they may give some clue as to why yours are not locking up.
I see here it says, "Auto lock hubs engage / disengage via either electric, or vacuum servo." http://www.fordf150.net/forums/viewtopic.php?t=40758
Also, here is someone discussing, "F-150 and have no 4wd. Seems the auto hubs will not lock in." http://www.f150online.com/forums/other-powertrain/223-anyone-problems-auto-locking-hubs-look-here-semi-long.html
"There is a known problem with the auto locking hubs" and "Ford has determined a design defect and has made a replacement part for them."
Now I read this, "97 and on F-150's use a totally different setup. No more locking or unlocking at the hubs. Has half-shaft from each front wheel to diff with 2 CV joints in each, like a FWD car. The disconnect is in the diff, on driving the two half-shafts, and has locking dogs. Activation via vacuum line. Transfer case disconnect of front drive shaft is still there. Automatic hub breakage will be a thing of the past."
Is there any vacuum lines or anything going to them hubs except the anti-lock brake or speed sensor wires?
It appears to me there are vacuum lines, a solenoid
I also see parts listed as Wheel Bearing and Hub Assembly 4WD; Heavy Duty, OE Design, w/ Bearings and Races (Front) , Axle Hub Left Hand Drive 4WD (Part Time Drive) ; With Base Payload Package , Axle Hub Left Hand Drive 4WD (Part Time Drive) ; Heavy Duty Payload Upgrade Pack , Wheel Bearing and Hub Assembly 4WD; Base Payload Package, OE Design, w/ Bearings and Races (Front), Locking Hub Vacuum Tube , Wheel Hub Locking Actuator , Transfer Case Output Shaft Hub Spring With Electric Transfer Case , Transfer Case Output Shaft Hub Spring With Manual Transfer Case ,
I see alot of posts on those autolocking hubs.
"Go with Warn manual locking hubs. They have had alot of problems with the automatic locking hubs. You only notice that they dont work when you need them. I would get Warn manual locking hubs and be done with it."
"I switched over to manual hubs last summer after it started trying to engage by itself. I assumed the hubs were giving out and were locking in on occasion. I went with the warn premium manual locking hubs. I think they were around $85.00."
This is interesting.
"That's a known problem with those hub locks - the fix is to lock them (read your owner's manual or your sun visor) & drive around for ~200 miles to wear-in the front diff. Any time you back up, you have to re-lock the hubs until you put 200 miles on them. The problem is actually in the front diff; not in the hub locks."