Technical Out of Balance "Feel" - out of ideas, got any?

Kinda yes! The misalignment in the trans mount, which I initially didn't appreciate, puts the trans mount in a twist. The engine mounts are front mounted, flathead, donut style mounts and sit nicely, until the trans mounts drop a quarter inch or less, but the motor mounts accommodate that. But this is in my car, not the car in question.

Chris

 

I just happened to put a dial indicator on the rotor one day, thinking the casting was out of round or the bearing bore was off center or something and making the vibration. Then I thought, what the heck? I put a button on the indicator and ran it over the studs while it was still on the spindle and WAH-LAH!

So I talked to Speedway about it and they said they had some problem with that, when they re-drill the GM rotors for Ford pattern. GM bolt pattern is 4 3/4" with a 7/16" stud. So when they re-drill them for Ford it needs 1/2" studs and they just offset drill the 7/16" hole. It just barely cleans up on one side and the drill wanders around. That's how the bolt circle gets out of round!

They did send me another rotor even though it was on the car for 7 years, but that one was only out .020". That's when I decided to go with Johnny Law Motors for the Mopar rotors. They come with the right studs and the right spacing, so there is no re-drilling. Problem solved, I just wish I'd found it 7 years sooner.

 

Cool! Johnny Law to the rescue. Glad you got to the bottom of it, and it sounds like you did.

 

I had a similar problem with my roadster. The culprit turned out to be the fancy chromed bracket on the 8" Ford rear center section that the Panhard bar bolts to. I must not have torqued the bolts enough and it loosened up and was letting the rear end oscillate side to side. Potentially really serious issue but I found it before something awful happened. Tightened them up (and checked all the other fasteners on the chassis), problem solved.

 

Isn't Johnny Law a Hoffman group company?

 

Yes, but in this case they likely only marketed rotors produced by another firm.