Significant Vibration from Rear at 60+ mph

[Phoenix77]

My 2015 FiST vibrates significantly at 60+ mph. Before and after front tire replacement & alignment verification.

The vibration is not in the steering wheel; rather, coming up through the seats and I see the passenger seat shaking.

I went ahead and had both rear wheels balanced and the problem persists. Tires in great shape; no flat spots, no exposed or broken belts. Rims aren't out of shape / damaged.

Vibration at 60+ mph persists whether accelerating, braking, or coasting. Rear brakes are not stuck.

No noise to indicate bad wheel bearings. The chassis has 163k miles on it.

I welcome any input on possible issues.

Thank you!

 

[SteveS]

Ever seen a car going down the highway and a rear tire is bouncing/shimmying as it goes down the road? That might be happening to you. Usually due to worn out shocks and possibly worn out bushings.

 

[Intuit]

Rotate your tires to see whether the vibration follows. You can temporarily swap out a suspect with the donut. (keep in mind the speed limit on its sidewall)

Consider the possibility that curbing it has created excessive lateral runout on a wheel.

You'll also want to verify that the calipers slide mounts are good. Often, they'll only lock-up once heated up; then break loose like nothing ever happened when cooled.

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