4 wheel drive on 2005 f150 fx series not working. When going forward slowly like going up a hill, all four wheels are pulling. But when I gas on it the back tires start to spin but the front aren't so it seems sometimes it seems to transfer more power to the rear. In reverse only the back wheels turn no matter how hard I press the gas.

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Sometimes they get stuck and will not come OUT of four wheel drive. Try resetting the 4 wheel drive button and drive forward and backward several times.

Check and make sure it didn't blow a fuse. If it blows it won't allow it to do anything.

hi
yes seems like you switch is faulty.]
replace the switch
Thanks

Hi,
Yes, this is normal while in four wheel drive on pavement.
I will try and explain why.
In four wheel drive the front and rear drive axles are linked together by a chain in the transfer case and gears in both axles. This is a direct link with very little play between the front and rear axles.
When cornering a rear wheel will spin faster, or slower depending on the direction of the turn. this causes a binding in the drive line because the drive line wants all the wheels to turn at the same speed. So the wheel "skipping" going in reverse, is the drive lines way of compensating for the different speed of the wheels turning.
Never should a four wheel drive be used on dry pavement. I could cause a break in one of the drive line components. On a slippery surface , snow, mud, gravel, grass, There is enough slippage in the surface to aloow the driveline to compensate for the different speeds of tire rotation.
So do not try at highway speeds on dry pavement.
Your four wheel drive system is working just fine.
Wayne

the front axle locks in at the front wheels by vacuum there is two solenoids on the passenger fire wall that control the four wheel drive be sure those solenoids work there is an updated solenoid also check vacuum lines down to each front wheel area if there is good vacuum down to both front wheels the it is probably the diaphrams in the front wheel area.

Does you model have manual front wheel hub locks?

check to see if there is noise coming from either side of the front wheels. jack all four wheels and turn on four wheel drive, if one of the front wheel is not turning then the actuator on that wheel is bad. the actuator is vacuum activated so also check the vacuum hoses go to the wheels.

mounted to the tranfer case you will see what looks like a window motor. Round with wires coming out. This is the actuator motor for the four wheel drive. A lot of times if they are not used the brushes will stick in the motor and if they do the four wheel drive will not engage. Sometime you can tap on the motor and it will work. You also will have a fuse for the four wheel drive in your fuse panel. Good luck, hope this helped

Sounds like the electronic switch or plunger is going out.