[Chevelle-List] Help: Rear end and driveshaft vibration problem

[Craig A. Ellis]

Hello again, fellow Chevelle owners. I had to unsub for a while due to vacation and some seriously pressing business, etc. Anyway, I've been vexed with a serious driveline vibration this summer that is defying all of my attempts to fix. It begins in fourth gear around 2600 RPM and increases in intensity up to 3200 where it smooths out because the frequency is so high by then that it is not so annoying. My speedo is out at the moment so I don't know the MPH but the vibration does NOT change if I downship to third. Thus, I believe it is driveshaft and rear-end related. It is vehicle speed related, not engine speed.   I've installed a brand new stainless steel driveshaft (from CCI in Detroit) and ujoints, double checked it for runout (it's perfect), installed a new pinion flange (again, from CCI), and I already had a new ring & pinion and new Moser axles. The trans has been rebuilt and seems perfect. The motor seems well-balanced and the front end components are tight (it does not feel anything like a front-end problem anyway - it's not a shimmy, etc., it is a vibration you feel in the seat of your pants as well as the steering wheel). I even have new Edelbrock wheels (409's in 17x8) and BF Goodrich g/Force KDW's, but there was no change in the vibration from my old stock SS wheels and old-fashioned meats. BTW, you can see a pic of the car (unfortunately, with the old SS wheels) at www.neagroup.com/chevelle.htm. Everything I've tried seems to have improved the problem in steps. The most recent trick is I flipped the driveshaft and it got a wee bit better but still no joy. The pinion flange made a big difference, as did the driveshaft. But it is still not smooth enough to cruise the expressway at 65 without aggravation and worry.   I am open to any ideas any of you might have. I am at a loss as to what to do next.   Craig Ellis Port Huron, MI