I was having a vibration problem recently, thinking it was a universal joint in my aftermarket driveshaft ( sorry I have a 2005 f150 4wheel drive extended cab)
but the u joints all seemed tight, on a whim I grabbed and shook my front driveshaft and holy wah the thing rattled front and back! So I replaced both u joints with no major problems considering my limited mechanical abilities (woodworking is more of my thing) and low and behold I no longer have my vibration issue!

My question is why was my front driveshaft spinning as I’m tooling down the road in 2 wheel drive and is that a problem for me?

 

The front driveshaft spins any time you're in motion, same with the front diff and CV shafts. The hubs are vacuum actuated which is how it locks into 4x4.

 

Thanks! Like I say, woodworking is more my thing.

 

Alright I m confused. If the hubs are unlocked and transfer case is in 2WD how is the front driveshaft being turned?
If the tires are transmitting motion to the CV shafts the hubs are locked. If the transfer case is transmitting motion to the f. driveshaft it's in 4WD.

 

The front drive shaft should not be spinning in 2wd

 

What I've been told is the front hubs are vacuum actuated. They're under vacuum when in 2wd, but when there's no vacuum it's in 4x4. I thought I had been told the shafts all moved during 2wd operation, but I guess I was either told wrong or made an assumption. So, what would cause his front driveshaft to spin when in 2wd?

 

vacuum issue (such as a leak (poss leak in lines or solenoid problem)), broken / stuck IWE, issue with the transfer case disconnect / transfer case motor

 

Check vacuum going to hub actuators, if getting good vacuum, check each actuator... they’re prone to the diaphragm tearing or leaking. If both of those check out, you may have a bad actuator solenoid.

 

Neither the front driveshaft nor the half-shafts should be turning in 2WD, assuming everything's working properly.

 

the hubs on my '05 were locked in and wouldn't disengage. had to put new hubs on it and new vacuum hoses. so far so good