Specific Vibration: V6 4H Only > 55MPH, Butter Smooth in 2H

[Merninater]

I just bought an '07 V6 Sport 4WD ~115K miles on it. It recently passed MD inspection. It rides butter smooth in 2H on the highway as fast as I could ever want it to go 80+. However, when I use 4H (can shift into 4H <62MPH), I pickup vibration in the front end/steering wheel above 55MPH. I need to get the car on jack stands and start checking for any loose steering/suspension/axle/etc.

Silly question... could an old/loose CV axle be the culprit here? I know its related to the front drivetrain because it drives butter smooth in 2H. The vibration comes in high speed 4H everytime. I honestly don't know what components in the front end are under load in 4H and not in 2H. Of course the front diff. But wasn't sure about outward from there like axle, bearing, etc. Thanks for any/all input!

 

[MikeinNH67]

Why would you need to go that fast in 4WD mode? Are you doing this on wet or dry pavement.

Worn/unbalanced CV's can certainly do this. Many say OEM only on front wheel drive cars as aftermarket can bring high speed shake.

 

[Merninater]

No stipulation in owners manual about max speed in 4H. Lots of feedback on this forum also about the 4H in V6 and V8 models being same.

Hoping someone may have similar experience to me or also might have insight on what components in front end are under load in 4H that are not under load in 2H.