NOT good vibrations

[493 Mike]

OK, so the project was on hold for a few months. Finally decided much of the cause had to be 60-year-old week rear springs. So took the plunge installed new springs made by Detroit Eaton Spring, and they have made a very significant difference. The shuddering upon acceleration is gone and the vibration at higher speeds has also been eliminated. HOWEVER, there is still a drone around 35 miles an hour and again from 45 to 55 mph.
Plan is to go ahead and install the 2° wedges that I ordered on the theory that we seem to be moving in the correct direction. (I have been scratching my head, wondering why the new springs didn’t eliminate the issue entirely but so be it.) Question, would you start with 2° wedges or perhaps 4°? Don’t want too much or too little. I have a feeling this will be a trial and error process. Any suggestions or ideas?

Obtain an angle finder and know for sure.
Mike

 

[oldkimmer]

What are the angles at now? With the trans 1.5 down u need to be at least at 3.5 down on the pinion. With a 60 year old trans mount I would think it has to be squished gown some. Try shimming the trans mount up first. That just may cure your problem. Kim

 

[TKMSavoy]

Kim, thanks for reaching out. Good idea, I have ordered a new trans mount for comparison purposes and will install it if there’s any significant difference. Would like to avoid using the shims if possible and again, not sure why I would need them with brand new springs. Will keep you all advised of the progress.

 

[TKMSavoy]

Kim, thanks for reaching out. Good idea, I have ordered a new trans mount for comparison purposes and will install it if there’s any significant difference. Would like to avoid using the shims if possible and again, not sure why I would need them with brand new springs. Will keep you all advised of the progress.

Well, I finally have some good news to report. As I noted previously, the new springs helped but after period of time, the same original original bad vibrations returned at the identical speeds they always had. Apparently it was not the springs. I bought 2° shims and planned to put them in, but kept scratching my head thinking it just didn’t make sense (especially with new springs) that the car suddenly needed to be shimmed when otherwise it is in absolute original condition. The only other reasonable source of vibrations was the ball and trunion joint in the driveshaft. Even though I rebuilt it twice and it seemed to meet all specs I couldn’t Shake the idea that it’s probably part of the problem. So, I took a dive and ordered a new driveshaft from inland Empire driveline services in Ontario California. Installed the driveshaft and it turns out the ball and trunion was the problem. The vibrations are gone. And with the more modern slip yoke no need to wonder about the ball and trunion anymore. Thanks for everybody’s input and help for a shade tree mechanic like myself this was a puzzle.

 

[sam dupont]

under acceleration: front u-joint, under deceleration: rear u-joint. Have you crawled under it and put a gorilla shake to the driveshaft?

I knew you were correct

 

[493 Mike]

I remember back in the early 70s, I had to shim the trans mount on a new car, under warrantee, to eliminate a driveline vibration. The dealership had the funky magnetic tool that attached to the u-joint cup end to verify the angle. I did "fix" it.
Mike

 

[TKMSavoy]

Thanks, Sam and Mike and everyone else —- drive train vibrations are terribly annoying and as I found not always easy to sort out. What would I do without B Bodies