318ti Intermittent Vibration from Rear

[M52ti]

Hi all,

When driving on the highway (around 65-75mph), my car will occasionally begin to vibrate violently. It gets worse very quickly as I continue to drive. Once I slow down to 10mph and speed up again, the vibration is gone. It has done this about 4 times in the past 6 months, with the last 3 occurring within the last couple weeks.

It's as if it catches some frequency and only clears when you slow down to stop the oscillation.

The car has a 3.73 LSD out of an e30. The PO said the RTABS were replaced.

Any ideas?

[spidertri]

Have you inspected anything at the rear? Is it definitely coming from the rear? Strange that it doesn't happen everytime.

Wheels balanced? Wheel bearings good? Diff/subframe bushings good? What material are the bushings made out of? Are the rear shocks blown?

How do the guibo and center support bearing look? How are the motor and trans mounts?

Check the hatch floor from above and below where the diff ear mounts for tearing sheet metal. If you see pulled out spot welds there is an issue.

[M52ti]

I have no inspected the wheel bearings, diff/subframe bushings, guibo, or CSB. It's definitely coming from the rear - I can feel it in my seat, not so much in the steering wheel.

The tires are freshly balanced. Motor mounts are new. Trans mounts look good.

It has no-name shocks and springs that were installed a couple of years ago. They should be fine.

The bushings are all regular BMW rubber.

I was hoping to see if anyone has had the same issue before I start throwing parts at it.