"Clunk"

When I go from drive to reverse I get and jurk almost like it's a bad u joint but since 928 does not use u joints kinda at a loss. Also am geting a vibration when going down the highway I can feel in the driver seat. Not sure if the 2 are related or not. Anyone have any ideas what that could be?

There could be a lot of causes for either of your symptoms.

Assuming you are talking about an automatic, a clunk can be caused by idle revs being too high, a misadjustment of the cable going to the transmission, a vacuum problem, or other things.

The torque tube bearings are known to fail, causing vibration. I don't have any personal experience with the symptoms, But I would be sure to eliminate tire imbalance first as a cause of vibrations when you drive. If your car has sat a lot and/or the tires are old (common with hobby cars not driven a lot), they can cause a lot of vibration even if they are balanced, and of course, unbalanced tires cause vibrations that are worse at specific speeds.

Thank you for responding. As far as the clunk, and yes you are correct it is a automatic, what's is a good place to start. Because it does it also going from reverse to drive or drive to reverse. So I don't think it's the rpms being to high because when I go park to reverse it is pretty clean. I was doing a lot of reading and vacuum lines seems to fit but am not sure. Would you recommend checking the vacuum lines 1st then go from there.

Sometimes the rear flex plate rivets come loose; The factory fix is to install bolts.

The torque converter bearing (in the transmission housing) can also wear/fail.

Does the vibration peak at a particular RPM, or continuous across the RPM range?

billvvSU wrote: Does the vibration peak at a particular RPM, or continuous across the RPM range?

Very important to know the answer to this question.

Has the crankshaft end play been observed?

Get a flashlight and visually check that all 4 CV joint boots are in good shape.

Rais rear wheels, once up turn each rear wheel back and fourth to see how much play is in the cv joints.

But as others have mentioned it could be something else.