15-20 MPH Vibration on Acceleration

1987 300E. On acceleration there is a vibration between 15 and 20 mph which feels like going over rumble strips. Light and hard acceleration produce the same symptom. The vibration seems to get worse as the car
gets driven longer. For instance, when cold, the problem is really not noticeable. After 45 minutes of driving it is very noticeable. Except for this vibration, the car accelerates beautifully.
I have recently replaced all of the rear control arms, all 4 coil springs, a ball joint, a tie-rod end, the steering idler arm bushings and all 4 tires. I also had a recent alignment. The car runs straight and smooth as fast as I care to go.
Based on the symptom getting worse as the car is driven longer, my thought is that this is a rubber part failing. I would appreciate any thoughts of where to start looking and how to identify whether or not the various parts are failing.
Thanks,
Robert
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Prop shaft rubber doughnuts?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I'd start the search at the drive shaft's flex joints, then the motor mounts and last the rear axles' spider (CV) joints. The axles can be had rebuilt if that's the cause.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
hey change the overvoltage relay located at the back of the battery. Its has a red plastic on top. I had the same problem
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
9kman wrote:

There's your problem. Dig into those deep pockets and get a new car instead of fixing the old piece of shit over and over.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.