Okay, the Vibration starts about 50mph through to 70mph. It shakes the entire car-very little if anything coming through the steering wheel.
Steps taken 1)balanced wheels twice with different machines with no difference
2)swapped all four tires from my other car with no effect
3)replaced driveshaft support and bearing with no difference
4)replaced one rear axle shaft and right rear control arm after it collapsed no change in vibration
5)replaced engine and transmission mounts
6)replaced steering damper
The left front caliper is sticking, and it could use front shocks. The tie rod ends and upper control arms and a ball joint are about a year old and still okay. The vibration is speed related-no change with engine rpm or when shifted into neutral. Smooth as can be until 50mph then, it just goes into a crazy resonance until about 70mph. The amplitude gets lower after 70mph but, it is still there.
WT$@&% should I be looking at?
Any help would be great

how is the driveshaft u-joint? are you sure the driveshaft is balanced properly?

__________________
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

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The driveshaft ujoint was replaced - wouldn't that be evident at lower speeds during 1&2 gear accel? Went to pick up some window switches(they were wrong-it was an 87300sd not a 82300d like the ad said) and got up to about 95 mph and could feel it in the wheel a touch and some weirdness in the front end generally so I'm going to get it up on a lift tomorow and double check everything

It's good that the u-joint was replaced. They will sometimes wear sort of a notch in them due to operating in almost the same place all the time. I have cured the vibration when this has been the problem by putting a washer on the passenger side of the carrier between the carrier and the body. This causes the u joint to operate in a slightly different position. Since you've replaced the joint this is not a factor.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

Are you sure that the driveshaft parts were marked before disassembly and then assembled back to the same relationship with each other? If they are not, the driveshaft loses its balance.

__________________
2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

When you fitted the propshaft did you let the car settle on its wheels and push it backwards and forwards a bit before tightening the centre support mount and the two big nuts?

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

How did this problem develop? What work was done prior to the problem?

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

It would be useful to differentiate between a wheel vibration and a DL vibration, as their frequency will differ by a factor of 3. An axle problem might seem like DS vibration also, as the three-lobed spider in concert with a 3.07 final drive ratio will offer the same frequency as an OOB driveshaft. To possibly eliminate the axles as a problem, add weight to the trunk so that the axles are running perfectly straight and see what happens.

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'83 300D, 126K miles.

I'd also suspect an imbalanced rotor or hub combined with worn shocks. Good shocks will overcome a minor imbalance.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Okay here is an update-the axle I didn't replace has about an inch of movement in and out-so I guess I need to replace it. Also the r front outer tie-rod end is pooched.
I will report back after I scrounge up some more money and time. Funny that the boots aren't ripped, no leaks or noise but, like I said-an inch of travel in and out. Ugh

Thank you for all the advice so far
I'm starting to hate this car
Cheers

Hate it in to submission, but stick with it. It will get better!

How are your flex discs on the driveshaft?

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
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Axles are supposed to have that travel, so that the axle can change length as the suspension goes up and down. Axle in/out movement is NOT your problem....

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Yes, true, play should be checked by twisting/rotating the axles by hand. Easier to check with them off the car.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!