Hubs won't lock in auto postion

[Dan"gerous"]

I have auto/manual locking hubs on my f-250. Playing around yesterday in the snow I realized the hubs wouldn't lock when I switched to 4x4. No matter how far I drove. Only when I got out and manually locked them did they lock. Any idea what's up??

[jmartinez]

i had the same problem so i pulled the vac line off the hub turnd the air hose down to about 20 psi blew threw it and found a leak if you dont find a leak doing this it could be the vac silinoid

[troid123]

Very common problem, I think that is why ford went ahead and added the manual locks as well.