I remember when I bought my brand new '90 Miata it did the same thing at 65 mph. Ended up installing a rear cross brace, solved the problem when nothing else would. Beginning in '93 they were installed from the factory.I think most if not all challengers have this problem, no matter what model you have. Call Ryan at stack performance, they make a cross member brace that just about eliminates the vibration completely.
Dont think so - have experienced warps before on many vehicles and there is no issue below 120Km/70MPh - this is consistent from day 1.You may also have warped brake rotors.
1 - Possibility - will check with #4 below..I am not aware of any TSB (Technical Service Bulletin) regarding a vibration problem. If its not warped brake rotors, you should check the following:
1. Insure that your tires are in spec. roundness wise with a dial indicator. (F1s are problematic).
2. Confirm that the small metal clips that the factory uses to hold the rotors on during the assembly line process are all removed from all 4 rotors.
3. Insure that all the lug nuts properly torqued.
4. Get a road force balance (see link below).
Hunter GSP9700 Wheel Vibration Control System
Found it - "Tinnerman Push Nuts" - follow the embedded link - #10 in the first listI am not aware of any TSB (Technical Service Bulletin) regarding a vibration problem.