Ok I have a 77 z28 with a 350, T5, and 3.73 open diff. A while ago when I started to let off the clutch it would slightly shake the bodyand drivetrain. Over a few months it got REALLY bad to where if I used 1st gear the shake would be so bad that I used 2nd to take off. If I slowly drain the clutch it is ok in 1st, but other than that I have the worst take off .So far I have replaced the engine mounts, clutch, machined the flywheel, changed the u-joints, and replaced the leafsprings. NOTHING has helped and I'm out of ideas of what it could be.
Oh also I recently upgraded from my super T 10 to a T5 and there was no difference.

PLEASE HELP

 

Just out of curiosity, have you checked the driveline angles? I'm putting a T-56 in my '77 and have not checked the angles yet, but I plan on doing that before I put it back on the road. With a leafspring car it should be pretty easy to adjust. I don't have the number of degrees each should be but a google search should get you that number. (for both the tranny and the rearend.) I hope you get it figured out..... weird vibrations are a bitch.

Bryan

 

Yea the angles can be no more than 3 degrees, I was thinking about it today and maybe when I take off the axle is rocking back and making my angles go out of spec. Will ladder bars stop my axle from rocking?? let me know please

Also your car sounds like it will be awsome let me know how the progress goes