Front-End Vibration on Acceleration

[engineeering]

Ok. My issue is not new. I already searched around on the forum and found a few people discussing this but no posted updates or "SOLVED" threads.

I have a 2006 AWD. I have a vibration on acceleration (in pedal/front end). If you let-off and step into it again it goes away. Note also.. I do not feel it in the steering wheel. Tires are new/balanced and no issues there. No issues with front drive shaft off. So here's my logic.... either CVs, Driveshaft, Front diff assembly, bearings, or ball-joints.

CVs - Could be an issue here. I would expect harsher vibration on corners while accelerating but I have not noticed this to date (lift can be harsh on CVs. Note also... my truck is supercharged and has an extra 110hp... so that does not help high-angle CVs). As far as I know... original CVs have about 200,000 kms (~130miles) on those parts.
Front Differential Assembly - i recently swapped 4.56 gears into the front. No issues initially. Maybe a bearing or something is going in the carrier assembly. I guess I can drop a bit of fluid and see what it looks like. Difficult to access and no drain plug either. So I would have to pull all bolts and break new seal to probably find clean fluid. . Probably a good way to eliminate things though... all new Yukon parts and was installed by a certified dealer with a good reputation. Also, no issues immediately after install.
Driveshaft - I have a custom-shortened driveshaft. I knew I might have issues here when I had it manufactured cause they are difficult to balance. But after I did my manual swap I did not have any vibrations initially. I attribute this to the shaft being balanced and true. Also, I have new u-joints that are well-greased. So I don't suspect anything there. I should re-check all connections for looseness now that I think of it...
Bearings - I would not think this would be affected much by acceleration... rather cornering. So I don't think this is the issue. But I've been wrong before.
Ball Joints - I've had ball joints do odd things before. But I don't really feel it in the steering wheel. So I don't think this is the issue either.

Some additional info... hopefully it does not distract from the symptoms but may be useful.
I have a slightly different setup however, I have a Manual Swap so I have a shortened front drive shaft... additionally.. I just switched to 4.65 gears. Issue developed sometime after the work. I also have a 2.5" lift. ​

Here is a link to an older post with the exact same issues/discussion. No final updates or marked solved.
http://www.explorerforum.com/forums...whirr-and-vibration-when-accelerating.424122/


So, can people please chime in? I've already taken it to my Yukon installer once (a few months ago) when it was first developing and we couldn't hear/reproduce any symptoms and I have already paid extra shop time. I want to see what I can diagnose soon since I have a 1 year parts/install warranty.

Want so get this truck ready for the summer fun!

Thanks all!!

 

[07EddyB]

I have no freaking idea. But with all those mods good luck tracking this one down. You mentioned no issues with the front drive shaft off - I assume you've look at the ujoint?

 

[engineeering]

Yep. Didn't see anything on the u-joints. It seems to have a bit of movement at the joint where it bolts up to the transfer case but I think it's normal (axial/linear movement only I think).