Front Driveline Vibration in 2wd with Part Time Kit, Free-Wheel Hubs, CDL and 7-pin mod

[Jackal301]

I've been seeing a few other driveline vibration posts with lots of helpful comments so I thought I'd throw my interesting case into the hat of knowledge:

I have an old part time kit from Slee, free wheel hubs (it came with AVM hubs), CDL switch with 7-pin mod. I didn't put the kit on, it came like that when I purchased in 2018.

Since I lifted my rig more than 3 inches (Dobinsons 3.5" VT Springs), I have gotten the drive-line vibration/grinding sound on deceleration when coasting and there is no load (no throttle and not slowing down yet) AND IN 2WD. I have Dobinsons caster correction plates as well. It only happens when I have some decent speed going, between 30-75mph.

Some other info that doesn't really matter: 37" tires. 4.88 gears.

I watched a few videos on installing the part-time kit so I could figure out if there is still power going to the front driveshaft when the CDL switch isn't locked. I really couldn't see how there would be any power since you remove the spider gears.

I have not taken the driveline off yet, because I keep getting stuck on the fact that the driveline shouldn't be spinning at all. I can freely spin it by hand with almost zero resistance when the truck is parked.

Can anyone explain why the front driveshaft would still be spinning in 2WD even with everything I have installed? Does the transfercase mod still allow some power to the front without the CDL locked?

EDIT: The vibration is more of a sound than a vibration. The truck doesn't shake. It sounds like a grinding/high frequency vibration. The frequency is fast, it is definitely being caused by a rotating part. It's hard to explain. You can feel it a little, but the truck definitely isn't shaking.

TIA!

 

[cme4lyt]

How do you know/why do you think your front driveshaft is still turning ? Your vibration may be related to something else, not necessarily the front driveshaft ?

I‘m guessing your front driveshaft is not turning and the vibrations to feel/hear are related to something else. If you think it’s in the front, could it be related to wheel bearings ?

 

[Jackal301]

How do you know/why do you think your front driveshaft is still turning ? Your vibration may be related to something else, not necessarily the front driveshaft ?

I‘m guessing your front driveshaft is not turning and the vibrations to feel/hear are related to something else. If you think it’s in the front, could it be related to wheel bearings ?

I just rebuilt the front end. The old wheel bearings looked fine, and I replaced them with new Koyo bearings. Still same exact vibration.

 

[retrofive]

Pull the front drive shaft?

 

[Jackal301]

Pull the front drive shaft?

I am going to do that this evening. My question was that it makes no sense that my drive shaft could be turning or getting power. Is there still power to the driveshaft (even if it's less than 1%) with the part-time kit installed in the transfer case? Or could my drive flange or some crazy coupling going on in the axle to force the birfs to turn even when the hubs are unlocked?

 

[benroberds]

what ever happened here? I've got the same sort of sound going on. Almost a tinny type sound. Seems to be a very constant spinning sort of noise. Doesn't really seem to vary with speed. I installed the 3:1 gear set in my t-case and also have 3" dobinsons. Worried it something in the t-case but that job went very smooth with no obvious issues.
Did you ever come up with anything?

 

[crx7]

I have the same issue with the Dobinson 2.5VT fronts, however, I am still AWD.

 

[benroberds]

I took my driveline out and drove around. Same noise. almost like a very light chain dragging along. Intermittent this time.

 

[nothovi]

I took my driveline out and drove around. Same noise. almost like a very light chain dragging along. Intermittent this time.

Does this sound similar to what I captured here: