Vibrations and knocking sound at certain speeds

So I've been fixing some minor things on the machine lately and noticed some strange vibrations occuring when driving on the Autobahn. This only happens above ~120 km/h (~75 mph) and not while accelerating or braking but only when rolling with a bit of throttle.

As there was also some knocking sound from the right hand side when cornering at slow speeds (~40 km/h / 25 mph), I checked the outer and inner CV joints on the right hand side. The inner one seemed to have a tiny bit of radial play. As the parts were here anyway, I changed both CV joints on the right hand side today, got everything back together and yes, the vibrations are a lot less but still there. I also still have that knocking sound when cornering at slow speeds after driving for some miles (doesn't seem to be there when everything is cold).

I'm pretty sure this is still from the right hand side. What's left are wheel bearing (then again that would be noisy all the time I suppose) and half shaft bearing (the one that supports the inner CV joint on that side). I didn't notice any play at all in that bearing though.

I did notice when mounting the new inner CV joint there is a tiny bit of rotational play between the joint and the drive shaft. Maybe 2/10th of a mm or so.

Could it be the differential as well? Or maybe the inner joint on the other side?

Hi

On other cars I have experienced that wheel bearing can make noise only when cornering. And sometimes mostly 1 direction.
This phenomena mostly at the early stages of worn bearing.

Cheers
M

It doesn't sound like a wheel bearing from your description - you would expect a constant drone whose pitch/tone increases consistently with car speed. As said it can often be more significant when cornering, or even reduce when cornering.

More common for the rear bearings to go than fronts too.

What came to mind while thinking about it a bit more: Could it be a tooth missing in the differential?

When I had that - in fact, two opposite teeth missing - it just ticked a bit, barely noticeable except when driving the wheel by hand with a head under the gearbox.

So the best idea might be swapping the left hand side drive shaft (or CV joints rather) for another one to see if it goes away? :-P

Further investigations: The knocking sound is there when doing ~40 kph, off the throttle (getting worse when braking) either going straight or slightly left. Looks like it's one of the CV joints on the left hand side. Well, that should be fixed in about two hours. New front shocks need to get on anyway, so just a tiny bit more work once the shocks have arrived.