pulsing rear end vibration at highway speeds
 

hello everyone,
i need some help. driving down the highway i've realized there is a pulsating vibration from the rear end.
at highway speeds.. (above 60mph) a vibration occurs for about 2 seconds, then goes away and the car rides smooth as butter for about 5-10 seconds then the vibration comes back. this seems to happen all the way down the highway. its *slightly less noticeable once its warm.. this happens only on the highway. i've had the car doing 60 or so on a larger back road so to speak and i don't notice it. At first i thought it was the highway... but now not so much, issue with the car.
ive already ruled out the possibility of:
-unbalanced wheel
-bent wheel

>if it were a whee unbalancedl, it would go away at speeds over 70mph and it does not.
>i have 3 sets of wheels for this car and they all do it so its not wheels.. where do i look next? hub bearings, maybe a worn bushing in the back somewhere? i can test lateral runout of the face of the hub at the shop but i dont think this is a factor.
thanks

perhaps shes out of alignment, i can try and put it on the alignment machine tomorrow an see how off it is. not sure if being out of alignment would do this.
also seen people checking the "guibo" / rubber disc between the driveshaft and trasnmission.

If wheels are perfectly balanced and wheels are not bent, then next items to check are flex disc and the [drive shaft] center support bearing.

You can check the condition of the flex disc without having to dismantle things because it's [partially] visible. Center support bearing is buried behind the heat-shield that's behind the exhaust pipes.
Depending on the mileage, you may want to think about replacing the flex disc and the center support bearing. To replace the flex disc, you will need to drop the exhaust system. After going thru all that, you might as well replace the center support bearing and be done with it.

I am planning to replace the flex disc and center support bearing [as a preventive maintenance] on my car this summer.

#2 and #8 in the picture below.

I will be sure to take a look at it tomorrow and post back. Any idea how hard it is to take apart the drive shaft like that to replace parts? I'm not convinced it's a part d the driveshaft.. I thought if it was it would be bad at all speeds? Car has 146k miles on it. Not sure if it's original or not. A shop did some rear end work to this thing before I purchased it.

I had one on an old 528e go out many moons ago (guibo bushing) What you are describing sounds like the same as I had. Mine had a crack in it and it wasn't really visible until the shaft came out and taken apart. When I looked, I was looking for it to be clearly broken and if I had known exactly what I was looking for I probably would have seen it while on the car.

Did you replace the centering bushing that has to be pushed into the driveshaft as well? I'm taking a look tomorrow. I'll bring a good flashlight and inspect for small cracks. How hard is it to drop the deiveshaft to do it?

I am also having this same issue, although I am not quite as sure my tires are perfectly balanced... so I will be getting the wheels balanced this weekend. I also would like to know how hard this would be to do. let me know what you find.

In order to replace the flex disc and/or center support bearing, we need to bring down complete exhaust system (everything past catalytic converters/resonators). Then remove the heat-shield. After that, you will have full view of the flex disc and the center support bearing. To remove the flex disc, remove 6 bolts and use a long heavy duty pry bar...

Pos
 

Found out today the diff is going bad. Rear wheels are bent.
So I have to spend 2-300 on straightening the wheels first.. Then see how bad the diff is.
Really sick of this car. Love it to death but the amount of shit it needs is stupid.

Will a diff fluid flush and fill do me any good?

Never, and I repeat never buy used wheels. Honest people and money making will never be compatible.

Oh that SUX! To answer your question I did not change the center bearing, just the rubber disc.