I don't know if I should curse a blue streak, or lay down in a fetal position and wimper a bit...
So I got the rear from my 70 installed in the 73, installed the driveshaft, filled it, yada yada. The we put the shafts back in as per FSM, .008" to .018" play.
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We also put new backing plates on the car (from a donor car). The ones on the car were quite worn where the brake shoes rubbed on the pads. See below where my finger is pointing.
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Then we put it back together with all new brakes and the brake drums from the 70, in case there was an issue with the drums being imbalanced.
Result. Same *^%$@! vibration.
I am really at a loss here.
- This car has had two different balanced, blueprinted engines. No change in the vibration.
- This car has had two separate transmissions. No change in the vibration.
- The driveshaft has been balanced twice. Then it was shortened for the Gear Vendors O/D and balanced yet again. No change in the vibration.
- I just swapped the rear to a totally different rear. No change in the vibration.
- I checked the axles carefully. The bearings operate smoothly and in nice shape. No change in the vibration.
- I have had two different set of drums on the rear brakes. No change in the vibration.
- I have had two completely different sets of wheels and tires on the car. No change in the vibration.
The final potential (?): When I quasi-restored the car in the early 90's, I replaced the tired leaf springs with a set of Hemi leaf springs. I still remember that the ISO bushings in the suspension did not fit great, since the leaf springs were thicker than the original ones. Could this be placing the rear differential in a bad location and causing the vibration? I already tried to shim the rear a bit, but perhaps the shims were "overridden" by the ISO bushing and so the rear really didn't end up being shimmed at all?
I don't know. The wind is out of my sails at this point and I'm running out of time. If anyone has any other ideas, I'm all ears...