[pontiacmark]

Here is a crude drawing of the angle relationships. This is showing the driveshaft parallel to the ground, even though that is not exact.

[bluebandit]

Mine started out with the shifter buzzing. Thought it was loose or bad shifter bushings. Then later it started getting a little vibration in the car that gradually got worse. I kept checking things like you till one day I was under the car looking around checking the ujoints. When I grabbed the front of the driveshaft to check for play in the joint I could feel the shaft move up and down some in the bushing. Replaced it and vibration quit. I figure the driveshaft could use a balancing too.

[rod cole]

If youre pic is accurate that is way wrong. Do you have a manual for any rear wheel drive car? Because most have a diagram of proper angles. The angles should be paralell. Do You understand the concept? The only way it could get that way is if the center section had to rotate on the tubes either from being slammed into reverse violently. Or was hit in the rearend hard enough to make the driveshaft rotate the housing down.

[rod cole]

One other real possibilty would be the wrong upper or lower control arms I would measure center to center between bad car and good cars control arms. Thats all I have.

[Old Man Taylor]

With a stock A-body the angles do not end up being parallel, even though that would be best. At least my two did not. I also have very little angle at the trans, but I was able to get the rear to 1.5-2 degrees.

[rod cole]

Static that would be exactly correct. Mr. Taylor. Under load they would be parallel if you still have factory bushings. Solid racing bushings would allow less difference static because there is less movement.

[pontiacmark]

I knew the rear and trans should be within about 1 degree and the difference between the driveshaft and trans as well as the driveshaft and rear should be 3 degrees or less. I am fairly certain the car has been hit in the rear at some point as the rear bumper is somewhat pointed up relative to the body. Are '64-66 upper control arms shorter? Tonight I will crawl under and check the length of mine.

[tempest455]

Yes, 64 arms are shorter, they are 12.75" center-center.

[Keith Seymore]

Rather than try to explain everything with words, let's see if this helps:

[Keith Seymore]

...and here is the "thought process" that helps determine if you are working in the right area.

I hope this helps and I apologize if I am telling you something you already know.

K

[Keith Seymore]

Let me know if you have questions regarding some of the terminology; I am sure you are already familiar with the concepts but some of the word choice might be a bit foreign.

Also - if you think it would help perhaps I could start a separate thread for vibration diagnosis in general, including engine, trans, tires & wheels.

K

[pontiacmark]

Keith,
That is very helpful info. I followed most of the procedures in the flow chart. Reading back to one of the first pages, it stood out to me the comment that the vibration is more acute under load. That is the case with my car.

Eric,
The upper control arms measured about 10.25" center to center. So that is shorter than your '64's. I definitely would need longer to correct my angle. Anybody know what the correct center to center distance is for a '70 A-body?

[getmygoat]

I just measured some uppers I had laying around... I am 99% sure these are original 1970 GTO arms.

10 1/4 center to center.

[pontiacmark]

Getmygoat, thanks.

[tempest455]

Maybe is was the later was shorter. I can tell you for sure the '64 is a different length. OMT, you remember, we talked about this once before.

You said "new" driveshaft. How did you measure the old and who made it?

The only time I ever had a driveline vibration was, I just changed to 1350 series joint and had a new drive shaft made. The shaft was slightly too long. Under hard launches and accelration, the yoke would push into the trans and bind. This would cause a vibration. They shortened the shaft and all was good.

Reading all the above I can still say I have never had a vibration from pinion angle and thats including racing cars w/ slicks for years.

Veryify you have the correct upper control arms and move to another source like driveshaft, clutch, rear end and so on.

[Grant Miller]

In my hunt for a vibration in a 68 GTO, I noticed similar (If not identical) driveline angles. I shimmed up the trans to change the angle with no difference in the vibration. I then installed adjustable uppers and tried infinity different angles with no difference in the vibration. Even some very outrageous angles made absolutely no difference in the vibration.

[Old Man Taylor]

The '68 and up control arms are shorter due to changes in the body. Always use the arms for the year of the body, not the year of the rear end (except for the small ears on the '64 rear).

[sts]

Why don't you try a new set of axle bearings-possibly a new set of axles? (You don't know the history, and they could have however many hundered of thousand miles on them.) I had barked up the driveline phase deal for decades. I replaced the bearing and axles in my car--if I recall, it was less than $200--and the car is like silk at 100+ mph.

I'm not big on paying hit or miss or simply throwing money at a problem. The point is axles and/or bearings problems are textbook examples of the symptons you list. I did lots of homework on on drive line phase, even altering the angles with ZREO changes. Some mention that the angle listed is the desired number. Not that you want something like this jury rigged, but comments from a custom builder claimed that the angle can be off quite a bit without vibration being a problem.

When I was playing around with varying angles, I know for fact that I had knocked it out a good 5' to 6'. It didn't make one bit of difference as to the vibration: In other words, the difference you list, whether it's "incorrect" or not might not be the cause of the vibration. I'd start with the textbook examples of driveline vibration, then work back from there.

[stimpy]

Originally Posted by bluebandit

Just a thought but in case you have not looked at this yet check the tailshaft bushing in your tranny. It fixed the vibration problem in my 78 T/A that was like what you are describing.

I had this happen to my suburban and it vibrated from 50-60 mph , and a chevelle I had . the yoke shouldn't wiggle at all the one on the burb was ruined when someone tried pushing the yoke into place and gouged it , also I have had the splines on the output be screwed up from abuse it damaged the yoke splines and wiped the tail bushing ( the bushing was $150 to have replaced )

[pontiacmark]

At this point I wanted to keep it simple. I have two spare rear ends to swap in as well as for spare parts. One is Pontiac 8.2 the other is a Chevy. I will pull the axles and check their runout.