I have a '67 vert 2v 289 with a C4. Engine was just rebuilt 5k miles ago, and runs great at slow speeds.

However, once I get above 50 mph or so, the car begins to shake violently, but not always. Sometimes it's as smooth as an Audi. When it does shake, I can really feel it when I put pressure on the shifter slightly to N or 2nd. The tranny does shift rather hard sometimes.

At first I just tacked it up to the age of the vehicle. However, I recently sat shotgun in my co-workes '65 FB and his was super-smooth.

Could this be the motor mounts? Loose connections where the tranny connects to the engine or driveshaft?

Please advise.
 
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LILCBRA

I wish I didn't have all of these balls in the air
15 Year Member
Dec 6, 2005
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How are your U-joints? Possible worn tail shaft bushing, but probably unlikely. If you've installed a different transmission than stock (thinking something like a longer transmission such as a T5....) your driveshaft angle could be off. Just a few ideas for you, hope it's something easy for you-good luck!!
 

tos

Founding Member
Apr 27, 2001
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Cincinnati Ohio
Are there any noises or just something you can feel. I would definitely check jour u-joints for slop, Maybe check your torque converter bolts, tranny mount. Normally if an engine or tranny mount is broken or loose you can hear a thump when you stomp on the gas or let off quickly. Also could be a bad belt in a tire (rear?) - I had a belt go bad on a brand new set of name brand tires once and it would come and go also cause the belt would shift around (good one day, very bad the next)
 

tos

Founding Member
Apr 27, 2001
896
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Cincinnati Ohio
Your statement about shaking violently is what worries me. Normally not the sign of ujoints. Noisey, vibrating yes but not shaking violently. Let us know..
 
Your statement about shaking violently is what worries me. Normally not the sign of ujoints. Noisey, vibrating yes but not shaking violently. Let us know..
Actually just picked her up from the shop and the vibration is virtually gone! Drives really smooth! Got her up to 80 on the freeway just now and there was very little vibration. Maybe a tire imbalance?

I still want to take care of those u-joints before too long though.
 

LILCBRA

I wish I didn't have all of these balls in the air
15 Year Member
Dec 6, 2005
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Marietta, Ga
Did they tell you what they found? Loose lug nuts will do the same....