Heavy vibration under power

In my 98 Z3 2.8 5 speed, I get a heavy vibration, almost like a shutter, under heavy acceleration about 3 to 4000 rpm in all gears. Under normal, or mild acceleration, and at any road speed it is smooth. The Tech. at our BMW dealer here is stumped. We have replaced the shocks and links but no change. Now we are thinking it's the center support of the drive shaft. Has anyone experienced this sort of thing when going through the gears, and what was the fix? Thanks!

quibo?

There's an item called a guibo in there that can cause what you're seeing. Seems like you have a resonance under acceleration.
It could also one of the several constant velocity joints that is a bit worn.
The guibo is basically a built in shock absorption system for the drive line.
If I remember correctly its a rubber joint between the transmission output shaft and the drive shaft. Its hidden pretty well under the underside covers and should be inspected. Its usually on the output shaft of the transmission.
Sometimes there is a mid support for the drive shaft that could also cause something like this. The 3 (possible) cv-joints are drive shaft into rear end, rear end to right wheel, rear end to left wheel... if you have x-drive add 2 more for the front wheels.Not all vehicles use the drive shaft cv-joint.
cv-joints are more precise than universal joints and work smoother
In any event it is in the drive line somewhere.
You can check for :
loose wheels, bearings on drive wheels, cv-joints, guibo, rubber mounts for rear end,
loose hard point mounts for rear end, drive shaft, rear transmission mount, clutch.
Any of these could be responsible and it could be a combination of more than one.

Chuck

You didn't mention how many miles it has on it. Chances are it is the center support bearing and/or failing driveshaft U joints. These are the most common causes of the symptoms you have. When the driveshaft is removed to replace the bearing, the joints should be checked for play and the guibo should be replaced (it isn't expensive and has to come off anyway.) This problem can also be caused by a misalignment in the driveline, which can be caused by broken or collapsed engine and/or transmission rubber mounts, so have those checked as well. As cwb suggests, the rear cross member bushings should be checked, as they are prone to failure and can cause the rear end to shift around under power, but you would also notice handling issues.
cwbii-
Kudos for being helpful, but there is a bit of erroneous info in your post. There are 2 universal joints on this driveshaft. At the output flange of the transmission there is a rubber flex disc (guibo like you said.) The halfshafts each contain two constant velocity (CV) joints, but these would likely not cause this issue (and usually take many many miles and years to wear out.) Also, there are no X drive Z3s.

tx

I've primarily worked on 7's since this is what I've owned up till now... they definitely had a cv-joint at the rear (It was in the vicinity of $800 for a replacement).
I was not sure if that same level of engineering attention was paid to the 5's and 3's.
Universal joints are less expensive and more prone to wear & wobble... I've certainly replaced quite a number of them in my other vehicles over the years. The half shafts are the ones that see the use while providing power to the wheels while as they go through the full range of movement... so should be the first to wear out. Can't say as I have had to replace one though even though I did have to replace a wheel bearing assembly on one of my 733's. Multi-part shafts, center support bearings, etc tend to be used with a rear a-frame structure to assure good shaft alignment... again not what I had on the 7's.
I have 3 3's in the yard at the moment so I'm definitely going to become more familiar with them.
My son's 323i
2000 330i convertable (green/green)
2009 335d (white)

I appreciate your correction!

Chuck

Thank you all for your responses. My Z3 has 73,000+ miles on it, and this problem started probably about 7 - 8,000 miles ago. The BMW Tech. and I both believe it is the Flex Disk or the Center Support. I just wanted to hear what anyone here had to say on the matter regardless of our thinking. As the Bentley Manuel also says, It's a difficult thing to narow down. It seems that it's replace things till it goes away, or let it go till it comes out where we can find it. Thanks again for your responses.

Larry