So I had the front of my truck on jackstands this weekend to do some work on it. The truck was in 2wd, in park, with the back tires solid on the ground.
I spun my front tire by hand, just to make sure everything sounded and felt alright. When I did this I noticed the front driveshaft rotated. Also if I spin the one front tire the other front tire will spin the opposite way (I know that is normal for open differentials) but are either of these supposed to happen when the truck is in 2 wheel drive????

 

That's normal if it's not running. When the engine is running, vacuum disengages the front hubs and the front drive shaft and half shafts should not be turning in 2WD. If they are, you probably have a vacuum leak or bad solenoid.

 

Ok for some clarification. On a 97-03 F150 the front CV shafts spin all the time. The difference is there is a floating slip join on the passenger side of the front diff. It allows the front end to spin at different speeds. But the driveshaft does spin all the time when the front wheels are in motion. The vacuum diaphram on the front diff disconnects the right axle when the engine is running. Without vacuum it locks the the front diff. Do not worry as every thing is normal.

 

Oops - forgot to look at the year

 

Alright after some more searching.....
The front drive shaft engages in two spots, the transfer case and the front diff. From what I understand with the truck idling in park, in 2wd, I should be able to turn the front drive shaft by hand, correct? If I cant turn the front drive shaft by hand this means its either locked in at the diff or in the transfer case (which I'm sure its not locked in at the transfer case otherwise it would ride like crap down the highway and making turns)

 

It will not spin by hand if the front wheels are touching the ground. It is disengaged in the transfer case. If you need pics I have a broke down 8.8 and can show you what allows it to turn.

 

Well Im still trying to figure this out. I just went outside, started my truck, let it idle in 2wd and tried to spin the front driveshaft by hand. It wont budge.
Iv read multiple posts, some people say it shouldnt spin others say it should spin. like in this thread https://www.f150forum.com/f6/front-differential-38082/

 

Maybe it has to do with having a LSD front ? I have an open diff and mine turns freely while running in 2wd. Or it could be the axle collar as mentioned before. Maybe try just lifting the drivers side off the ground and see if it turns. should be free if everything is working as it should.

 

Sounds to me like your vacuum actuator is stuck in the locked position...

Remove the plastic guard from the from diff, (3) 10mm bolts

Check the linkage on the front diff from the actuator to the shift fork... It should be disengaged toward the drivers side... Pull the two vacuum lines off the actuator and you should be able to engage and disengage by hand

Grease up the push rod while you're there...

You ARE able to freely spin the drive shaft by hand when in 2H with the wheels on the ground if everything is functioning correctly...

Check that and get back to us

 

Thanks for the reply. I wont get to check it out tonight as it's getting dark out and I dont have a garage here at my apt.
I will report back my findings when I get it checked out.