Vibration / rumble beneath 64 convertible

[Kenneth L.]

I recently acquired this car. As I drive it more I have noticed a vibration that can be felt in the middle to the rear of the car, particularly upon accelleration (over 2000 rpm) or at higher speeds (>40mph).
Initially I thought it might be a U joint but these are all recent - major rebuild of drive line and suspension by previous owner.
It feels like something is out of balance. Looking underneath on a lift I did notice that the strut rods are a little bent (both about the same) and the rear trim height is uneven side/side. I don't know if these are related to my problem.
Has anyone had a similar experience? Any thoughts as to probable cause?
Thanks!

[Timothy B.]

Re: Vibration / rumble beneath 64 convertible

Kenneth,

Have you checked the tires by feel to see if they have any flat spots from sitting. This would be a eccentric when rolling and for sure be a vibration.

[Thomas W.]

Re: Vibration / rumble beneath 64 convertible

Kenneth - Maybe the driveshaft is out of balance? I believe it is recommended that driveshaft should be re-balanced when you replace the universal joints and done as an assembly. Might also be worth having the wheels/tires re-balanced, or at least rotate tires front-to-rear and see if vibration continues which might narrow it down to a drivline "issue" instead of a wheel/tire "issue".
Good Luck.
Tom

[Tracy C.]

Re: Vibration / rumble beneath 64 convertible

Could be the floor of the aft compartment drumming. There was a thread about a year ago on this subject and the original question was regarding the rubber pads that were on the #4 crossmember. The answer came back that the pads were there to damp the vibration of the floor in the aft comparment at certain harmonic levels.

I've lost the copy of the picture of the pads on the crossmember, but maybe someone else has one..

tc

[Dan H.]

Re: Vibration / rumble beneath 64 convertible

Kenneth, also do a quick check and make sure the seat track hold down bolts aren't too long and touching the exhaust pipes directly under them.

[Gene M.]

Re: Vibration / rumble beneath 64 convertible

Easy to check the u-joints for slop. And check that the rear end snubber cushion is in good shape and secure.

[Kenneth L.]

Re: Vibration / rumble beneath 64 convertible

Thank you all for the great responses. Many of these can be easily checked. I'll keep you posted on progress. Ken

[Kenneth L.]

Re: Vibration / rumble beneath 64 convertible

Hi all!
Thanks for all the leads.
I followed up on most. Ruled out flat spots on the tires, U joints, rear wheel alignmenmt and plug wires breaking down. Focus now is on differential supports and related hardware. Noticed that strut rods are bent and rear of car trim height is uneven side to side.
Will keep you posted. Further inputs appreciated.
Ken

[Michael H.]

Re: Vibration / rumble beneath 64 convertible

Hi all!
Thanks for all the leads.
I followed up on most. Ruled out flat spots on the tires, U joints, rear wheel alignmenmt and plug wires breaking down. Focus now is on differential supports and related hardware. Noticed that strut rods are bent and rear of car trim height is uneven side to side.
Will keep you posted. Further inputs appreciated.
Ken

[Kenneth L.]

Re: Vibration / rumble beneath 64 convertible

At long last here is the solution...ignition timing was misadvancing causing breakdown on acceleration leading to rumble/vibration. Replaced the vacuum advance and problem is gone. Adittionally, vibration was causing exhaust to hit seat bolt on driver's side aggravating the problem. Long seat bolt was replaced with proper length bolt.
Thank you to all for all of your help!
Ken