TCracingCA

tear or deform. Can you roll your car to where the driveshaft to the rear diff yoke is at the biggest angle to see if the rotation would be binding up the ujoint movement. I dont think the bolt shift is that much to cause such a serious angle into the diff to be feeling things clear from the back of the car, but then the driveshaft is designed with some movement for and after, so if the drivetrain is bowed in the center from a shift, is it causing your yokes to be pulled out as it rotates! I am thinking on that! Maybe someone else has had that specific problem! I have not had a tranny nose get loose or shift or driven one with that problem.

V8Heart

Today's updates: I finally got a chance to do a quick test after shifting the transmission mount to the original position and torque the bolts. It has been a little tricky and to obtain the best result I had to jack the transmission in order to relieve some weight from the mount. It is now 90% back to original position where washer's marks are.

Well went out for a ride and seems like the vibration is gone or almost gone. Will make a more scrupulous test on the highway in the next few days.

DansYellow66

Well, that sounds like it could be good news. Strange someone would elongate the holes to shove the mount over. Possibly a prior owner noticed that the motor and transmission is offset to the right and thought they needed to move the mount back towards centerline to straighten it out. Since the differential pinion is also aligned over to the right a similar offset amount that could create an issue.

V8Heart

Can't really tell what happened, it is just that going back to where it seemed to be in origin the transmission mount helped to solve the problem. As said, I need to do some more testing before giving the final response.
In the meantime thanks to everyone who contributed to this topic.

Frankie the Fink

That DOES come up on here once in a while....somebody thinks the drivetrain is supposed to be perfectly straight in the car.

I know that some have put on U-joints that banged the tranny tunnel and maybe somebody decided to scooch things over to avoid that somewhere in the last 50 years.

V8Heart

This makes me think of several possibilities.
Was it done on purpose?
Or was it just a matter of chance that the bolts were not torqued and the mount moved?
Is this something that the previous owners knew?
Or did it happened somehow during the long transport to Europe?

The fact is that the vibration was too invasive and should have worried enough whoever was driving the car.
Could it be possible that they were not aware of it?
Or they did just drove it below 60mph?

DansYellow66

Without taking my own mount out I'm going to say I'm 99.9% sure those bolt holes are not slotted to permit that sort of lateral adjustment. Someone probably got confused about the offset alignment or as Frankie suggested, did a Bubba to correct some interference of the driveshaft with the tunnel.

V8Heart

The two washers are different and now the driveshaft seems to be more centered into the transmission tunnel than before adjusting it.

V8Heart

Updates
Yesterday I made a correct comparative test to verify if the vibration was gone.
IT WAS NOT!
The reason why I thought it was gone is because the road I used for the previous test was not really what you can call a "perfectly paved road"...
I have to say that at the beginning it seemed that it got better, less vibrations, but then it went back exactly as it was before.

May check again if the bolts moved or have to go back to diagnosis stage

PS went to the garage this morning but the transmission was still in place and the bolts were tight

V8Heart

This time I rotated the driveshaft 180° as a possible solution read in many posts.
Well, I haven't drove the car till 60mph because now the vibration seems to be present even at lower speeds but as I said it really wasn't a proper test.
Should I go back to the previous setup and order a new driveshaft and u-joints?

DansYellow66

I think it would be worthwhile to pull your driveshaft and have a driveline shop check it for run out and balance. If it needs to be re- tubed that's not expensive, should be under $150. But, I have a feeling you have a tire issue. You might try swapping tires front for rear and see if that changes anything.

V8Heart

Swapping the tires was my first attempt, I also tried the wheels I have on my 68 but no impovement was found.
Here in Italy is really hard to find shops that calibrate and balance old American car's driveshafts so makes more sense to me to order a new one -the only one I found asked about $250

DansYellow66

If you are sure it's not tires , before throwing money at parts I would pull the half shafts, driveshaft and rear shocks and inspect them closely for bad u-joints and leaking shocks. Also poke around for missing or loose shims, loose trailing arm bushings and anything else you can get to. I wouldn't give up on finding a drive line shop to check the driveshaft. Most of them service truck and service vehicles - someone over there must do this.

V8Heart

I just removed the old driveshaft. You can see in the picture a comparison between the old and the new one.

Looking at the ends of old shaft, is it normal that they don't align as on the new one?

rtruman

Last year at a car show there was a 67corvette concourse NCRS
car this guy had this car for years .
He had exactly the symptoms you have with your car.
He had all the professionals look at the car for years no one could figure it out.
Well I had the same problem it was the exhaust touching somewhere
on the frame ,he had 2.5 exhaust on his car and the 2 inch holders
supporting the pipes at different speeds it touched and you could feel it thru the whole car.
Same with my car I took a ball pin hammer and put a small dent where it was touching underneath .
The guy bought me a thirty pack for fixing his corvette after many years.

Look closely at the exhaust first then move on .I think you will
find the problem.

V8Heart

I have side exhausts

rtruman

Still take a look make sure Bubba didn't touch somewhere and move on to plan 2

V8Heart

I really can't figure out what to look at since I don't have any exhaust pipe going to the rear of the car.
If you were pointing at the fact that a Bubba fix would be somewhere causing the vibration, well finding it won't be an easy task.
In the meanwhile let me know what you think about the misalignment of the two ends in my old driveshaft

rtruman

If you flip the new one over looks like it would match the old one
How much did that set you back and custom made or over the counter .
I am not a pro at this but the new driveshaft looks good to me. Bolt that puppy up and run it

GTOguy

That old driveshaft looks like it came up from the Titanic. Never seen so much rust. I would question its integrity.