Intermittent Vibration/Shake
 

I have a 1968 Ford Galaxie with an automatic transmission and a 428, I never had a problem before, we rebuilt trans and motor and now at high speeds I have a problem with a shake or vibration that starts then stops starts then stops from around 45 mph to any higher speed it just amplifies, any ideas???

First off welcome to the sight. Is the vibration in the steering or in the seat? there's a whole bunch of things that can cause shaking in a car at high speeds.this will just help narrow it down to the root cause

Most of the vibration is in the seat.

By the way thank you for the greeting it good to be on.

if I remember right that car has the old FMX trans. in it cause of the shape of the hogs head or the old C-6 they were round and didn't look like the ones out of the late seventies even though they pretty much had the same innards. the shaking could be coming from the drive line like a bad u-joint or a slightly out of balance driveshaft. next question is when the trans was rebuilt did you have it done at a shop or did you do it yourself?

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I had the transmission rebuilt at a shop, it is a C6 it was a FE car with a C^ in it, I am tending to think it is the drive shaft, I will do the repairs to that first and let you know, thanks for the input.