Front driveline help

[G35TR]

Alright, here's the deal. I've replaced all 4 u-joints, front and aft. Both axles had 1 dried up seized OEM joint. No problem.

But I still have this annoying vibration between 75-80mph. Also, when letting off the gas during the vibration, I hear a droning noise for like 1-2 seconds.

Well I figured maybe I unknowingly crushed some of the needle bearings on one of the u-joints when installing. So i take out both shafts, and check the joints. All 4 move around nice and quietly. All 4 seals look to be intact and fine.

Well I believe I've narrowed the problem down to the front driveline, b/c the vibration is mostly felt in the steering wheel, and the slow 4WD disengage problem is back again. Also, I put it in 4WD to see how that affected the problem (I know, 80mph in 4WD = no good). Anyway, truck runs smooth as glass in 4WD.

So I decide to leave the front shaft off and see if the vibration is still there, or goes away with the shaft. Interestingly enough, the problem remains with or without the front driveshaft installed. Not good!!

My question to you guys is, how much rotational play to you have in the front shaft when twisting it by hand (while in PARK)? My front seems to move a lot, probably like 1/2 - 3/4 inch. Seems odd, especially since the is no play what-so-ever in the rear shaft.
Is yours the same way?
Is my front diff. shot?

[disallow]

I'm pretty sure my front driveshaft moves some too... possibly due to the t-case.

If the vibration is there with or without the driveshaft, its gotta be something else, a tire, brake rotor, wheel bearing? I really doubt its your diff.

t

[skinny2]

Any chance it's just a tire balance issue? I've even seen slightly out-of-round tires that balance good but have a vibration. When on the balancing machine, you can see a slight "sway" in the tread pattern. Use of a road-force balancer is the best bet for getting those high-speed balances just right. It seems like you've hit most of the drivetrain related items.

[G35TR]

Due to any real lack of noise, other then the slight droning, I too tend to think it's probably not the diff.

As for the tires. I hope its that simple. Unfortunately since there are the rare times when it goes away completely, I have my doubts about tire balance.

I've had some off-road trips through some pretty deep water so I'm thinking it may be the wheel bearings. I'll look into more possibilities when I get a chance. In the mean time, any other possible culplrit ideas is greatly appreciated!

[SPICOLI]

My front driveshaft moves 1/8 to 1/4 of an inch max. I wonder if it's a steering linkage issue. Maybe you got a loose or worn out joint.

Do you get the vibration while turning or is it a straightaway issue?

[G35TR]

Well it happens @ 75-80mph, so I've only felt it on the highway (straight).