Bad Vibration at 2500 RPM and above

[Early Bird]

1969 383 Magnum. I am having a bad vibration at 2500 RPM it seems to be mid car no noise however just vibration. This car originally had an automatic transmission in it and now has a 4 speed and has had the vibration since it was purchased by my nephew. I have verified the harmonic balancer is the correct one. He was told the drive shaft could be to long and seemed so to me we had it shortened and balanced. I just pulled the transmission to check for the pilot bushing and it has the bushing but the yoke would not come out without a come along and hammer. Could be because he kept driving it with the vibration. Only had the four lower bolts in the bell housing. The first time we pulled the drive shaft it came out easy. The splines on the yoke and transmission look OK but will not slide together now. The clutch and pressure plate looks good also. I also put the car up on stands and ran it can't feel the vibration. Had the tires spun balanced also. Still was vibrating when on the road. planning to get the trans checked while out of the car. Could the bell housing flex with all of the upper bolts missing. The flywheel ring is a #2843 214 the original Flywheel should be #2843 211. The Flywheel that was installed is for an eternally balanced crank I believe. Hopefully I will find out next week.

 

[Coyote]

Replied to your earlier post. The splines almost have to be twisted. The missing bolts definitely do not help the situation. It could be driveline angle, rear motor mount, drivers side motor mount.

Universal joints could also have went “south”. The yoke is obviously a puzzler. Good luck, please advise what you find.

 

[Russ69Runner]

That sounds like U joints. Don't know why the drive shaft wont go back in Remember their is a larger spine on it and they have to line up. Must have all bolt's in the bell housing and might check the transmission support that is where you would feel it mid of the car. Russ.

 

[Early Bird]

Replied to your earlier post. The splines almost have to be twisted. The missing bolts definitely do not help the situation. It could be driveline angle, rear motor mount, drivers side motor mount.

Universal joints could also have went “south”. The yoke is obviously a puzzler. Good luck, please advise what you find.

I believe it is the wrong Flywheel. I will hopefully find out next week

 

[Early Bird]

Replied to your earlier post. The splines almost have to be twisted. The missing bolts definitely do not help the situation. It could be driveline angle, rear motor mount, drivers side motor mount.

Universal joints could also have went “south”. The yoke is obviously a puzzler. Good luck, please advise what you find.

Definetely the flywheel was the wrong one all vibration is gone. Found that there was no input shaft seal or gasket also the output shaft seal was gone all but the ring on the transmision. Found no twisted splines on the yoke or the output shaft. Replaced the yoke and it slides smoothly. She runs great I will have to go over everything and tighten all bolts and replace the manifold gaskets there is a bad leak.

 

[Russ69Runner]

Glad to here you found the problem. You must have not had the car long. Trying to find the problems that someone else left is hard sometimes. If you could have seen the metal replacement job on this car I have you would have had a stroke. Someone even tried to recreate metal around the back window with Bond O. What a mess. Well have a good one and enjoy driving her.