Not so sure about that -it has done it since 79, but I never brought it to the dealer to correct. I love this Z and that is the reason I've kept it for 42 years, but there were 84k of these built and mine was a June 79 build. If you saw how bad the fender gaps are and how the factory paint fades at the bottom of the rockers and the rear bumper, there are definitely things that snuck through QC in those days.I don’t believe the factory created this problem and couldn’t fix it under warranty. I ordered new 4 speed Z28’s in 77, 78 and 80 and never had a vibration. Maybe I was lucky but I dought it.