Deducing a cause and solution for shaking at speed

[kung fu jesus]

Thanks for the input! Had some experienced e30 owners look over the car. Their advice after getting the car in the air and riding in it was diff bushing, diff itself (unusual pinion lash), right side halfshaft (odd shudder while cornering and accelerating).

[I8UR911]

Center support bearing or driveshaft. Be 100% certain that there is no issue with the calipers as well.

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[kung fu jesus]

New rotors up front didn't change the symptoms. I inspected the calipers for bonding, cleaned and relubed the pins. The old pads showed no signs of uneven wear, either. All wheels and tires were balanced dynamically.

[cabriodster87]

Check brake rotor runout and excessive dragging from caliper piston/pin and make sure inner tie rods are good and tight..True story

EDIT: Static or Dynamic balance on wheels?

[kung fu jesus]

Wouldn't I feel it with my hand on the rear tranny tunnel?

[vpilarrt]

I would suspect the driveshaft support.

[kung fu jesus]

Yes, twice.

[vpilarrt]

Did you have the front end aligned after the rebuild?

[kung fu jesus]

I am revisiting the shaking in my e30. I am trying to deduce where to head next with locating, diagnosing and solving the issue.

65-80 mph shake in the steering wheel, I can feel the shaking in the seat, too. When I put my hand on the driveshaft tunnel between the front and rear seats, I feel no vibrations at all.

I switched out my wheels and tires with another set and encountered the same symptoms. Both sets of wheels and tires are freshly balanced. One set had had two different sets of new tires installed with a *little* help moving from 205/45-16 Continentals to 205/50-16 Michelin Pilot A/S 3s. The other set of wheels are 15" basketweaves with worn Bridgestone Star Specs (205/50-15).

In the past 5000 miles, the car's front end is rebuilt; new control arms, FCABs, swaybar links, rotors, hubs, inner/outer tie rods, steering rack, steering guibo, upper shock mounts and alignment. The car is on Billy sports and H&R Sport springs, maybe 50k miles on them.

In the rear, new shock mounts and spring pads.

The shaking doesn't always starts the same and the intensity varies. Sometimes on long interstate curves, the shaking diminishes or reduces. Sometime it does the same at varying speeds. It is a bit perplexing.

I have considered a driveline shake, but because I don't feel the tunnel vibrate, I am less suspicious of the driveshaft or half shafts causing this. Pushing in the clutch at those speeds to freewheel seems to have no effect on it.

Right now, I am now considering the RCABs and rear subframe mounts. I suspect I am getting an oscillation in the chassis through worn mounts and bushings.

I am welcome to suggestions, reasoned causes, personal experiences and solutions for this issue.

Thanks for the time and consideration!