I am posting this question here in hopes of catching some insight of some sharp guys on a particulary troublesome issue. I posted in this forum because I have checked the all of the obvious issues and I am not looking for the "did you check the u-joints?" answer.

Here it is. I have a high rpm vibration - out of the blue. Read my sig and that will tell you what were working with. I initially thought it was a drivetrain issue and even went so far as to replace all the bearings in the rear because I felt roughness in the pinion yoke. Upon further review, the vibration is not related to speed as much as rpm. I feel it in the shifter and the seat when I am at a higher speed AND higher rpm. Now, I am leaning more towards engine vibration as the car is not pulling as hard as it used to. Its not a huge power loss, but noticeable. The vibration only comes in under high speeds and high revs though. If your cruising at 75 in 6th - nothing. 75 in 4th - yes vibration. Im stumped. Could it be a valve sticking, causing an unbalanced engine situation? What else?

 

What are "all of the obvious issues" that you have tested and ruled out?

 

driveshaft needs to get balanced maybe?

 

I have not gotten into the engine yet, but I think I have ruled out drivetrain.....I did not have the shaft balanced becasue the vibration came out of the blue and the weight is still on the shaft.

 

Ok just checking, becuase if you havent looked at the engine side it should be discussed in a general engine tech forum. Transfering, thank you.

 

on my pld Caprice my balancer (the thing the belt goes around) got a little crocked, it was starting to get loos. I could look at it while the car was running and see it wobling like bent rim.

I wouls say take a look at all the belt pullies and make sure they are not wobbling around at all.