My 240D is shaking, and I can't find the cause.
 

Between the speeds of 28 and 32 mph the front of my '79 240D shakes pretty bad. I rotated and balanced the wheels, checked wheel bearings for excessive play, replaced both flex discs and center bearing on the drive shaft. The car drives pretty straight, and rides smoothly at all other speeds all the way up to 75 mph.
One other odd thing is that I some times get the same shake when the car is going about 10 mph with the brake on, but it brakes smoothly at higher speeds, so I think the rotors are fine.
The shake also occurs while the car is coasting in neutral. Any ideas? Thanks,

Otto

The only SOURCE of vibrations are ROTATING components, almost always wheel/tires or driveshaft. Vibrations are AGGRAVATED by loose suspension or more commonly steering linkage components.

That said, you have a vibration ONLY at a specific speed (frequency) so it could be a static component such as steering linkage, etc. If the vibration is driveshaft speed rather than wheel speed, it could be a loose carrier bearing or other driveshaft related component.

Since more than 90% of vibration problems on cars are wheel/tire related, you need to ENSURE that the wheels are balanced CORRECTLY. It is all too common for the tire store kids to put wheel weights ONLY on the inboard lip of the wheel saying that customers complain about the ugly weights being seen on their alloy wheels.

It is possible to get lucky with weights only on the inboard, but rare. On all modern cars the suspensions are nimble and REQUIRE dynamically balanced wheels, meaning weights both inboard and out. I have gotten so frustrated with the tire stores that I bought my own Coats computer balancer so I could balance them correctly without having a fight with the tire store kid every time.

Good luck,

Otto

Do you feel it in the steering wheel more than any other place?

Check your steering dampener and also steering links, such as tie rod ends.

Haasman