66 250s RPM shake! Please help!

[rhinosaross]

Hi All,

I am new to the forum, as well as to my 1966 250s. Since I purchased the car, it has had an annoying RPM based shake that translates through the chassis into the cabin of the car. It is driving me nuts. I have gotten the engine running smoothly (smooth idle and revs via exhaust note) but the car continues to shake around 850-1,000 RPM, but smooths out in lower and higher RPM.

I have just replaced the motor mounts, engine shock, transmission mount, and now front subframe mounts. THE SHAKE IS STILL THERE! I'm fixing to lose it real quick if I cant figure it out. I am fairly mechanical, but this is the first old mercedes that I have had to diagnose and it's a bit different than most other things I've dealt with. PLEASE let me know your thoughts. It seems almost like the engine is "out of balance" but from what I've read the m108 is an internally balanced motor, so that seems to rule out the balance theory.

So let's hear it, out of balance crank pulley, broken fluid coupler in the tranny or something? I'm open to ideas.

Help me help this car!

Thanks,

Riley

[bcbens@embarqma]

Sounds like it could be out of sync carbs or a vacuum leak. If this occurs only at idle or just above idle.

[68_280SE]

Have you checked the driveshaft flex disk and the driveshaft center bearing mount? They are both rubber and can cause all kinds of problems when they are deteriorated and worn out.

John

[rhinosaross]

Originally Posted by bcbens@embarqma

Sounds like it could be out of sync carbs or a vacuum leak. If this occurs only at idle or just above idle.

I'll check those out, I've checked for vacuum leaks with the old brake clean spray and wait for an idle change, and it doesnt appear to have any, I'll try and look into the carbs though!

Thank you for the input.

Originally Posted by 68_280SE

Have you checked the driveshaft flex disk and the driveshaft center bearing mount? They are both rubber and can cause all kinds of problems when they are deteriorated and worn out.

John

I have looked at the flex disk, but the problem occurs in park as well, so I think those are out being that they arent engaged and it still shakes. Thank you for the reply though!