Shuddering Under Load

[SnoqualmieE30]

I have had an extrememly persistent problem with my car shuddering under load. I have a 1990 325i and the vibration is tied to speed, not RPM. At 10mph, it is louder and sounds like a rubber mallet softly hitting a wooden desk. It's also a low frequency vibration, more of a shuddering or like something is sticking out of my driveshaft and is hitting something. At about 13-18mph, the sound is almost silent but I can feel it under the seats. Higher frequency and like im driving over road turtles (but not as bumpy). After 18mph it is completely gone. Does anyone know what this might be? I have replaced my transmission mounts (which were a nightmare, but it did little to help the vibration), and also my guibo (also looked like a nightmare but also did almost nothing to help the vibration.) I've looked and can't find anything on other people with this problem. Oh and it's an auto transmission. Vibration not tied to shifting. Vibration occurs not matter what gear its in and does not change with shifting between gears.

[jlevie]

That is pretty much a classic description of the symptoms of binding u-joints in the drive shaft and the failure of the center support bearing bad u-joints cause. I think an inspection will reveal tears in the rubber mount of the CSB. Replace it and the drive shaft.

[SnoqualmieE30]

Noob question: can you replace the center bearing and u-joints without having to replace the whole driveshaft? If I remember right I think I've seen u-joints and center bearings for sale on PelicanParts.

[N2MYE30]

No need to replace drive shaft.

[SnoqualmieE30]

No need to replace drive shaft.

I'm sorry did you mean "no, I need to replace the driveshaft" or "there's no need to replace the driveshaft"

[KVF]

I'm sorry did you mean "no, I need to replace the driveshaft" or "there's no need to replace the driveshaft"

I'll give you the more long winded explanation. He meant the latter, BUT while an entire DS replacement isn't "required" it's certainly the easier way to go. If your u-joints are toast you must find a way to get them machined out and have new ones pressed onto the DS. Many shops won't even bother, and will tell you that they only offer a complete DS with serviceable u-joints... This is most likely why jlevie cut to the heart of the matter and said to just replace the whole DS. Good luck.