SOLVED: Alright, help me troubleshoot this shake...

[thrillcat]

UPDATE: Lots of good info in this thread, but if you want to skip to the solution, go to this post.

I've done a ton of searching, a ton of reading, and I've already done some things, to no avail. Yes. It's another shake/vibration thread.

2005 X5 4.8is, right now it's at 111,900 miles.

Things that have been done in the last 3000 miles:

• SOME front suspension work, I believe just the lower control arms (this was done prior to purchase).
• Front brake pads & rotors.
• Wheels balanced.
• Brake Booster Replaced.
• Spark Plugs Replaced.
• New Front Rotors Machined.
• Wheels Balanced (different shop).
• Rear Drive Shaft Replaced.
• Rear Drive Shaft Guibo Replaced.

Not all of this was done to specifically troubleshoot the shake, just wanting to be complete.

What I'm feeling is a shake, right under my thighs, around 1500RPM. It doesn't happen right away when the X is cold. It feels great for the first 15 minutes or so of driving, but after the X is warmed up, it vibrates pretty much non-stop.

I feel it right under my thighs. If my knee is resting on the door handle, I feel it there, too. I've even seen it in the driver's side mirror. I also feel it in the steering wheel. I think I feel it in the shifter, too, but I can't be sure. It's a big enough shake that I think it's just shaking pretty much the whole vehicle. This isn't a subtle shimmy, it really just starts to shake. Once it gets to shaking I can even hear the shake.

I just got it back with the drive shaft work completed on Friday. Didn't have a chance to drive it on Saturday, but yesterday I took it out and basically the drive shaft didn't change anything. No better, no worse. I do NOT hear the whine that would point toward a wheel bearing. I don't hear any strange noises, no suspension clunking or creaking, nothing until I can literally hear the shake.

The one thing I did notice yesterday that I hadn't noticed before is that, once it starts shaking, when I start slowing down to come to a stop, the shake completely goes away upon a downshift, I believe it's from 3rd to 2nd, though I guess it could be from 2nd to 1st, not positive. But it's like it instantly goes away upon that downshift.

I'm hoping to build a punch list to go through. I had convinced myself that it was still suspension issues until my indy suggested the drive shaft. Then he put it up and pulled the drive shaft and the CV joint was super rough, so I guess I had my hopes up that "yep, this is the problem". Well, it wasn't. I'm ready to have this thing fixed.

I'm not even mad that I just dropped cash on the drive shaft, I'm all about fixing things before they completely crap out, but right now my priority is taking care of this shake. It's preventing me from enjoying the ride.

So, thoughts?