Sticky rear u-joint?

[Flash]

Trying to help a friend diagnose a problem but pretty sure i know what it is, but would like some input. I havent looked at it yet underneath since someone has my floor jack but just have description/symptoms.
The car feels shaky from the tunnel all the way up to 30 MPH, ive had bad CSB/rubber before and its not like the thing is hopping around. It hums in the tunnel and you can feel it when you put your hand near the backseat.
Not like it matters, but its a 91 325i.

Thanks :)

[EyExR]

Have you done any work prior to the shaking which may have led to this?

[Flash]

Have you done any work prior to the shaking which may have led to this?

I replaced the CSB on the offending car about half a year ago since the rubber was torn but have done the job countless times, properly preloaded it and installed the heat shield back in place (was missing prior).
The diff mount bushing didnt show signs of damage or excessive cracking at the time.

thanks

[FLG]

Does it get worse under acceleration? Usually a bad u joint will be much more pronounced when your on the gas and quiet down when your cruising.

Sent from my Galaxy Nexus using Tapatalk 2

[Flash]

Does it get worse under acceleration? Usually a bad u joint will be much more pronounced when your on the gas and quiet down when your cruising.

Sent from my Galaxy Nexus using Tapatalk 2

It does go away when you push the clutch in and let it coast, still has a vmmmmmmm sound but not like when you accelerate up to ~30 MPH. After 30 it quiets down until you cannot hear it.

Thanks

[jlevie]

I replaced the CSB on the offending car about half a year ago since the rubber was torn but have done the job countless times, properly preloaded it and installed the heat shield back in place (was missing prior).
The diff mount bushing didnt show signs of damage or excessive cracking at the time.

While it may be something else, there is a very good chance that the drive shaft u-joints are the problem. In almost all cases, a failure of the CSB rubber mount results from bad u-joints. Temporary relief can be had by just replacing the CSB, but the only real fix is a replacement drive shaft.

A clue to that being the case is that the vibration will be worse when accelerating briskly in the lowest gears.

[Flash]

While it may be something else, there is a very good chance that the drive shaft u-joints are the problem. In almost all cases, a failure of the CSB rubber mount results from bad u-joints. Temporary relief can be had by just replacing the CSB, but the only real fix is a replacement drive shaft.

A clue to that being the case is that the vibration will be worse when accelerating briskly in the lowest gears.

thanks bro. It ended up being the driveshaft rear u joint, there was obvious play in it and the surface of the metal was shiny, indicating that there was play-and upon moving it there was.

[CarsSuck]

What exactly does a bad U-joint feel like? Wobbly, notchy, grindy? While I was working with my father on his car, I noticed the middle u-joint felt loose and moved very freely, while the rear joint felt snug (but still easily moved by hand) and had a detent-like feeling in each bearing range of motion. So just what should I be feeling for?

[jlevie]

All you can check for with the drive shaft installed is play in the u-joints (there should be none). To check for binding u-joints the drive shaft has to be removed. Good u-joints are easy to move and feel silky smooth through the entire range of motion. If they feel notchy or stiff, the drive shaft needs to be replaced.

[CarsSuck]

Yes, I've had my driveshaft off and more recently on my dad's e21, so that is what I'm talking about. It sounds like both joints on my DS are shot (explains my high speed harmonic problems, but I dont have the other low speed symptoms other than being a bit jerky on/off the throttle). And one bad one on my dad's car.