This has been ongoing for a couple months now, I don't routinely go on freeways so it isn't a big deal but in the meantime I've been throwing parts at it to no avail. I've got 360,000 miles so I don't mind throwing parts at it as I plan to keep this car for awhile, engine and tranny are perfect.

The shaking usually starts mildly around 55mph and gets pretty bad around 65-70. What is odd is that every now and then it will feel fine, then the vibrations slowly start happening again. The rest of the car doesn't seem to be vibrating much, just the steering wheel.



Anyway, here are the parts I've replaced recently trying to figure this out:

Wheels
tires
inner tie rods
outer tie rods
struts
strut mounts
control arm bushings
brake rotors
alignment

ball joints were replaced a year ago

It's gotten a tiny bit better but nothing dramatic. The rack is not the original, previous owner replaced it around 3-4 years ago. It's got a ZF stamp. I've had a lot of 80's MBs before which all had steering gearboxes so I'm not super familiar with troubleshooting racks. It feels pretty tight, little to no slop.

I am also an amateur astronomer and this hobby takes me down some washboard dirt roads that can get pretty hairy but I'm pretty careful to keep the car from ever bottoming out. That being said I do routinely carry a large amount of gear (300lbs+) down these washboard roads for miles and miles which can't be too good.

I have a replacement pump I'm going to put it... not sure if it will make a difference but the current pump bearings don't sound too great.

There is a little bit of steering resistance on cold mornings (30-40f) for around 10 seconds but aside from that the steering feels great.

Any ideas? As I mentioned before, the car has plenty of miles and gets pretty abused, if I have to just keep throwing parts at it that is fine by me.