Thanks for the clarification, it should work...

Your numbers are very similar to mine. I added the shim to make the rear end point up towards the front 2.7 degrees.

IT MADE NEGLIGIBLE, IF ANY, DIFFERENCE

I feel your pain.  Thinking there may be side to side variation, but have not had opportunity to measure it.

Just Curious MS, now that you have the 69 on the road with a T-5, do you have any vibrations and what are the angles for that car?

I am going to put mine on a 4-post lift Sunday and re check all of the angles along with the pinion bearing. I do know that my pinion on the Explorer 8.8 is dead centered. 

I'm going to check the angles on my buddies 68 Cougar as well, it has a small block and T-5 with the stock 8" rearend.

I'm at the point where I would spend just about any amount of money to resolve this issue, it frustrates me every single time I drive my car to the level that it takes the fun out of getting it out of the garage.

I know exactly when it started, the moment I started changing things.

When I brought it home it had sat and not run for several years, once I got the stock 289 running with the C4 and 8" rear, all was fine, NO vibration.

I swapped the first 5.0 (306) and T-5 with the Explorer 8.8 at the same time and the problems started.

I have had 3 different motors and 2 different trans in it and the motor has been shimmed up/down and the Trans has been shimmed up/down with little change.

I will say the only constant part has been the 8.8 rear end, and I have rotated the pinion several times with little change. 

Right now, the motor/trans is down 2.7 & the pinion yoke is pointed down towards the ground 1.7

I know this isn't good, I had several people say that the pinion would rotate up under load and I believe that, but at gear changes or launching. I believe the pinion stays close to where it is set while cruising. With the trans 2.7 down, I am going to try rotating the pinion up to be parallel with the trans. At 1.7 down and trying to match the 2.7 of the trans, I will need a 4.4 shim. I'll try that, if by some miracle it helps, Ill cut the perches off and weld new ones on in the correct location.

My other concern is the actual operating angle of the u-joints at both ends. right now, with the trans down 2.7 and the drive shaft down at .7 is good, but when I rotate the pinion up from 1.7 down to 2.7 up is will not only change the rear u-joint operating angle but it will change the slope of the drive shaft, I'm just not sure how much, the drive shaft could be flat or headed up.

When it was stock, it was slow, dependable, and smooth.

The 69 does not vibrate. Nor is the car lowered.  I am
Just not willing to move the 66 suspension back to a stock height.

Bearing Bob wrote:

I sure see a lot of vibration complaints from guys with a T5, or one of its relatives.

I know MS and I have talked about this.  Didn't Ford have a ten pound chunk hanging out parallel to the driveshaft on a number of cars.  I also recall that the 8.8 in the Heap had one hanging out over the rear U-joint too.   Zugly, butt if it stops the jumping around might be worth a try.

kardad.......(just spit balling here)
Is it smooth under acceleration...and just starts around 70-ish when you level-off on the gas?
After seeing those videos guys have posted of how the diff goes up & down on the least amount of torque being applied...
well I'm amazed ALL cars don't vibrate & growl under power!
Guess my point is....if there IS one...the rear springs wrap UP on acceleration (even mildly) and down on deceleration &
braking. Have you tried stiffing the front part of the leaf spring? or replace  the whole spring if 'old'? Or maybe some type of traction bar...just to see if that makes any difference. Me tinkz the up or down degrees of angle on the rear end goes 'completely out the window' once you're under way. Not say'in it ain't important cause it IS..just .......
Sure you've balanced ...rotated...swapped...tires and rims....
Drum brakes on the rear?!!!!...
Tried rotating the drive shaft u-joints 180 degrees?!!
You have 17" rims (like MS)......!?!
My 15" doesn't give me any vib problems (I don't think!)...could that be a factor?!
6s6

I’ve tried rotating the drive shaft,
I have 17” wheels and each wheel tire convo has a set location due to staggered wheels and directional tires.
I have Cal-trac bars and can eliminate all spring wrap if I want to pre load the springs.
Once the vibration starts it doesn’t matter if you are accelerating or decelerating it continues until the speed gets below 70-72.

BobE wrote:

My numbers: (as found)
Trans: 3.3 degrees down
Driveshaft: 1.7 degrees down
Pinion Nose: 1 degree down
 
I added a 4-degree shim to push pinion nose up:
Trans: 3.3 degrees down
Driveshaft: 0.1 degrees down
Pinion Nose: 3.6 degrees up
 
Subsequently, I removed the 4-degree shim and installed a 1” lowering block:
I didn’t take any measurements.
 
None of these changes (as MS indicated) “IT MADE NEGLIGIBLE, IF ANY, DIFFERENCE”
My next step is to also check the side variation.

I should have noted in my original post that I have a T-5 trans and I originally had an 3" aluminum driveshaft and did try rotating it 180 degrees, no changes felt.
Changed the rear pinion yoke, verified u-joint is centered in pinion, no vibration change.
Got a new steel driveshaft, no change, rotated it, no change.
Had both driveshafts checked for balance and straightness, both OK. Re-insalled the steel shaft. 
I did purchase a transmission "counter weight" from a 2.3L Mustang, but couldn't bolt it up due to interference with E-Brake cables, and just haven't got back to it.
I going to get the rear end (9") rebuilt with new gears over the Winter and let post results. 
 

Quicksilver wrote:

Has anybody ever thought about a broken spot weld in the body? MS your car was hit once, Did you have the vibration noise before the wreck?

Always been there. Even with a 302 and C4

MS wrote:

Quicksilver wrote:

Has anybody ever thought about a broken spot weld in the body? MS your car was hit once, Did you have the vibration noise before the wreck?

Always been there. Even with a 302 and C4

 
Maybe it’s the roof oil canning at an 80mph resonance.

Ive been all through this as well. Right now I have the car jacked up and the rear tires off. Before I took them off I spun the tires and one of them would not turn because the brake drum is out of round. One of the "new" wheels are bought is out of round Im pretty sure. They are going to the wheel shop to be checked. It's interesting that a T5 is common. Drive Shaft King told me to bring it in any time and he would show me it is not the drive shaft. I have yet to do that.