Heavy engine vibration at 4k rpm

Hello. I am hoping some of you can help with this ongoing issue. I have a 1971 Buick 455 that had heavy vibration felt in the pedal. Replaced the harmonic balancer and the vibration at the pedal is now gone. However, now the vibration is felt underneath my seat near the trans/driveshaft area. I used a dial indicator to measure the forward and backward wobble and it measures between -.090 to +.017. Would any of y’all know this would be an acceptable clearance for the flywheel?

 

Have the drive shaft checked for balance,straightness and universals.

 

Huh??? What is "wobble" and what is "clearance"? Which "it" did you measure?

 

You mentioned "flywheel" so I take it is a manual transmission which would leave multiple possibilities, ... but if it's an automatic trans then just unbolt the torque converter and rotate it to the next position of the three that are possible. You can try all three to achieve the best results. I had a full size '91 GMC K5 Jimmy with a mid-vehicle vibration and moving that converter totally cleared up the problem.

Larry

 

It does not take much of a worn U joint at the rear end to make for a vibration, in fact the proper way to set the U joint into the yoke on the rear is by centering it with a magnetic dial gauge with measurements taken 180 degrees apart, and you want to see less then .010" difference!

 

I would agree that checking the u joints is the next most likely cause. Remove the drive shaft and check for play or a ratcheting feel to the joints. If they have never been done, it's high time on a 71 to give them a look.

 

The title states 4k rpm, ..... though I can't find any information in the OP stating the vehicle is moving while the vibration occurs. I believe more definitive information is required.

I have a '70 Corvette 4-speed that had a vibration that came and went at 3500 rpm. That never had to move an inch to diagnose. It was the original sintered bronze pilot bushing that was worn out. I remember it well as that is the root cause of me tearing the whole car apart for a body-off restoration.

Though the vibration is stated to be in mid-area of the car, you can disconnect all drive belts temporarily to check for an accessory issue.

Or once again if it happens to be an auto trans VS stick then you can unbolt the converter all together and push it back to clear the flexplate to test.

Larry