Trying to track down bad vibration

[Jim S]

I still have a bad vibration from about 35mph on up.  I can rev the engine in neutral up to 3,000 rpm and it's smooth as silk. But driving in gear the car vibrates.  I put it on jacks and removed the rear tires and it still vibrates running in drive, so it's not tire imbalance.  I also replaced the ujoints and the motor mounts and rear transmission mount.  I'm baffled!

[Gunslinger]

The driveshaft may need balanced.  

[Jim S]

3 hours ago, Gunslinger said:

The driveshaft may need balanced.  

That's the only thing left I can think of.  There's a shop about 50 miles from my house that can do it. If that doesn't fix it I don't know what will!

 

[64StudebakerAvanti]

How about driveline angles? I had a similar issue with a 64 4spd and it was due to the spacers missing.

here is discussion:

https://4xshaft.com/blogs/general-tech-info-articles/driveshaft-angles?srsltid=AfmBOor0wf1cMqW-8ZB44Bme-ZMX7e3iMTewwuTZlsJauargt1YjTgVj

 

[64StudebakerAvanti]

Not sure for Avanti IIs, but check that engine and transmission mounts are in the correct holes. For Studes, there are 2 sets, 1 for LHD and the other for RHD. 

 

[mfg]

21 hours ago, Jim S said:

I still have a bad vibration from about 35mph on up.  I can rev the engine in neutral up to 3,000 rpm and it's smooth as silk. But driving in gear the car vibrates.  I put it on jacks and removed the rear tires and it still vibrates running in drive, so it's not tire imbalance.  I also replaced the ujoints and the motor mounts and rear transmission mount.  I'm baffled!

Is the vibration a recent development… or has it been there since you purchased your Avanti?

[Stacey]

Had a 1967 Impala SS that developed a vibration, my first car. Thought tires/wheel balance, did not fix it. My dad said he thought a U-joint was binding, removed the drive shaft and sure enough the rear joint was dry and locking up, was not loose, but tight. Back then we were able to buy a new joint for about $5.00 and he and I replaced it, vibration was fixed. Might be worth looking at the u-joints.