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I have a 1999 F250 3/4 ton gas engine 4x4 with 110,000 miles on it. The truck as the switch inside the cab to put it into four wheel drive and although 4 high and 4 low light up in the dash I have no four wheel drive. After reading several posts I decided to change the actuator as it appeared to be locking up. After the change I put it into 4x4 and now I have the two back wheels turning and the front right wheel turning. When I take it out of 4x4 those 3 wheels are still turning. There is a red and a blue hose going to the actuator. The red hose has vacuum but the blue hose does not. Should there be vacuum at the blue hose or do I have a leak somewhere and what would be causing the right wheel on the front to be turning? Thanks
There is not a steady vacuum at the hoses. The hubs are locked and unlocked by a vacuum pulse.
Sounds like your hubs are bad. At this point they are probably junk and need to be replaced.
Your 4 wheel drive system is called Electronic Shift On the Fly, or ESOF. Search this forum for ESOF and you'll find a large number of posts from people with problems like yours and what they did to fix the problem.
You can try manually locking the hubs by turning the dial to the "lock" position. Unfortunately these ESOF hubs tend to like to sieze up if they aren't exercised regularly, so you might not be able to turn the dial.
Like redford said, search for ESOF and you will find a ton of info.
It sounds like the hubs are bad or the hub seal that seals the hub so it can use the vacuum pulses to actuate the hub. If you dont mind getting out of the truck to turn them I recommend manual hubs.