Vibration Issues (Driveshaft Suspected)

[1991S13]

'91 240sx Coupe

I just swapped my automatic for a manual, and everything is working great. The only problem I have is now between 40 and 50 mph there is a pretty bad vibration. This never happened with the automatic. My father thought maybe it is the universal joints, or the carrier bearing. Through process of elimination, we pulled the long piece of the shaft off and ran it on stands and it still shook. Then we pulled the short shaft off too to make sure it wasn't in the transmission, and it didn't vibrate at all. The driveshaft is from a salvage yard, so we thought maybe the donor car was wrecked pretty hard and that bent the shaft, so we put it in the lathe and spun it. It spins perfect without wobbling though.

I called the local Nissan dealer and they wouldn't help me without bringing it in, and the salvage yard I got the driveshaft from told me it was more than likely the carrier bearing (turns out the donor car wasn't wrecked). Im also wondering if maybe the rubber drive on the end of the shaft could have anything to do with it. The rubber looks kind of drywrotted, with a couple of small cracks. What do you guys think?

Thanks in advance, Kenny

[s13sr20chris]

driveshaft balance maybe? try slapping some hose clamps on it and rotating them to try to kill the vibration.

[elwesso]

you can take the driveshaft to a local driveshaft place and have them balance it for like $50

[1991S13]

UPDATE: When I spun the center bearing (I called it the carrier bearing in my first post) it wobbled really bad. This may be normal, but I replaced it, and that cured the problem.

Thanks once again guys,Kenny

[N.O. Accorderz]

i just changed my clutch and when i drove it afterwards i have vibrations around 2500-2000 when decelarating only...it does not vibrate when accel during that rpm interval...yall think its the carrier bearing too?