I have an 88 944 Turbo S, recently two problems have arrived. When I down shift from third to second or fourth to third the car shakes violently? and even breaks loose the tires from the shake. And my last problem is I can hear and feel a small vibration and humming in the steering wheel and on the gas pedal only while driving, the humming is coming from the front of the car. Even when coasting out of gear I can still feel it. I reved the engine while coasting and it was the same, the noise did not increase or decrease, but as I sped up the noise and humming was greater (out of gear, just coasting). which leads me to believe it a suspension problem. But what? TIA, Reno
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1988 944 Turbo S

 

I don't know about enough to break traction in the rear, but sounds like a transaxle mount to me. As for the front, probably wheel bearings, but possibly worn tires from not being in alignment. . . .