I recently bought my dad a 1964 Valiant Conv. ,1966-1967 slant six engine (re-built), original push button transmission (904 I believe)
Car starts great idles fine, very little vibration if any at idle. Give it a little gas and the seat and steering wheel vibrate. engine not so much. Car vibrates hard so hard I'm afraid to drive the car -- don't wat to tear something up.

Things i found and replaced:
1. had the wrong motor mounts (engine was sitting approx. 3 inches off) replaced no change in vibration.
2. changed transmission mount no change in vibration
3. adjusted valves 10 / 20 according to the book , they were off quite a bit. motor much quitter . no change in vibration
4. tune up with quality parts. (had a new tune up when i got it but parts were cheap) plug wires keep falling out off cap. no change

I pulled the trans to check the flex plate and torque converter. Front shaft of transmission shows some scaring, torque converter button shows some wear. button measures approximately 1 1/2", crank shaft pocket seems to be slightly larger hard to tell maybe a 1/8" larger.
flex plate is bent a little. I am ordering a new torque converter and flex plate.
Am i on the right path? Is there anything else i can try?

Thanks
Kenny

sounds like you may have a small hub torque converter with a large hub crank You may want to measure them with a dial caliper and report back with the dimensions.

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63 Plymouth Valiant Wagon

Sounds like a worn-out ball & trunion "U-joint" at the front of the drive shaft.
Usually the outer housing gets worn so you may need to convert it over to a newer & more common cross type U-joint with a"slider" yoke..
Most drive shaft shops can handle the job.
DD
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measured converter button 1.50 to 1.52, crankshaft measured 1.54, flex plate has one tab bent.

on another note the car has a rubber stopper in the transmission tunnel above the transmission that is crushed, should i replace it?

vibrations happens while the car in in park, drove it off the trailer and into garage. haven't had it on the road yet.

If the right side motor mount is upside down the car will vibrate a lot. I did this when installing a rebuilt engine in my '66 Dart.

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Joshua

Ok I'll agree with the idea of a bad B&T joint if it does this going down the road but sitting still? Wouldn't have anything to do with it at that point