did a couple searches and couldnt seem to find anyone with the exact same issue. anway i have a pulsing vibration at high rpms, right before shifting. 2-3 @ 80 it pulses considerably loud, but after 3-4 @ 140 the pulsing turns into a constant grind and you can hardly hear the engine. doesnt vibrate when just revving. bought the car like this with 60k on it. ive gone through the obvious, tranny mount, u joints, driveshaft, bearings, poly motor mounts.. then i did the more expensive stuff, tranny was built, new differential and gears.. im stumped. correct me if im wrong, but the front of the crank is internally balanced and the rear is externally balanced. is it possible that something caused the rear to be thrown off balance? thanks, chris

 

anyone run into this?

 

well i did some research and i have found that it is the drive shaft that causes this alot of the time. an aluminum replacement part# 10085375 from what ive found is the fix. anyone heard of this?

 

The driveshafts are notorious for causing vibrations at higher speeds (= high DS RPM, not necessarily high engine RPM). Put in 3.73's or 4.10's and the MPH at which it becomes a problem is lowered. The factory issued a technical service bulletin that allowed a lot of people to get the stock steel driveshaft replaced with an aluminum one, while the cars were still under factory warranty. But that problem is not specific to "full throttle" and high engine RPM. Sounds like you have a different problem.

What exactly do you mean by "pulsing vibration"?

 

the vibration is in waves, like a "throbbing". only seems to do it at the end of a gear before it shifts. as soon as it pops into the next gear it goes away until it starts winding out again. i did find a service bulletin from gm about this. says it is caused by beaming-?? between the engine and drivetrain. the fix is supposedly an aluminum driveshaft without a pinion damper. im not sure. but at thiss point im willing to try it. do you know where to find these things? couple places ive checked say that shaft is discontinued

 

Go to the "parts wanted" and "parts for sale" forums. Look for a "1LE" aluminum driveshaft. Aluminum driveshafts were also used in the LS1 cars, and are the same length. Note however that the aluminum shaft may not hold up to any significant power increases you may add in the future.

 

ok i have a driveshaft on the way.. but i noticed a small "wobbling" at an idle. kind of pulses, similar to the vibration, but a lower frequency. so the driveshaft is part of the problem, but what would cause it at idle? how easy is it to knock the flexplate out of balance? or is there anything else that would cause this?