I have been chasing the same vibration for years and it drives me crazy. Like most, everything was fine with the stock drivetrain. Then as soon as I decide to start making things better, we’ll you know.

My vibration starts about 75 and is bearable until about 80, and then just gets progressively worse, and you can not drive out of it. At about 95-100 it feels like something is going to fly apart.

5.0(331), T5 (2.95 first gear), Explorer 8.8 with Trac loc and 3.73 gears. 2006 MS Mustang front disc, Explorer rear disc. 17” wheels. First had the Explorer aluminum driveshaft, second a new steel driveshaft.

The Explorer 8.8 was narrowed by shortening the long side to center the dif.

I will get my Trans, Driveshaft, and pinion readings and post them to see how they compare. I have adjusted the pinion with shims multiple times and at times it seems to change the speed at which the vibration starts but never gotten rid of it.

I have tried multiple trans cross members and mounts. I have tried raising the motor as well with shims.

I would need to add cruise and set it slower, at 70 everything is extremely smooth.

Presently;
5.0 EFI, AOD, HiPO manifolds, 2"  Quiet flow mufflers and pipes with no crossover, 17" Cragar wheels, 12.5 GT front discs, 11.25 ish Explorer rear discs on narrowed (by me) Explorer 3.55 Limited Slip rear axle.  No vibration from O to 100+ mph.  No constant drone though I though I might have heard some during a strong cross wind.  No gear howl though I seem to hear some kind of "ringing" which no one else hears....Hmmmm, must be in my old head.  This condition has existed through two different home brew transmission mounts, with the AOD and 4R70W and back to the AOD.  Driveshaft is regurgitated from the 89 TC donor.  Exhaust has been changed from 2,25" with shortened Flowmaster 50's to the present setup with no change other than quietness.
Can't remember the exact the transmission and rearend angles but I seem to recall they were more than a couple of degrees....like 5 or so.  Maybe too close to zero causes a problem with the U-joints, who knows.
Back in the 8" days it did have a howl that came in around 45 and stayed all the way up.  Also had a minor vibration that came in at 70 but nothing like what MS is putting up with.  The 8.8 solved both problems. 
Wish I could come up with something specific to offer.  I guess I just dumb-stumbled into a mix that works.

BB1
 

Last edited by Bullet Bob (10/06/2022 8:06 PM)

Thanks, Glen

No doubt that can cause issues. I think they have a typo stating the 9” rear end is offset 15/16”.  It is actually 5/16” as shown in their picture.

The previous housing I had custom built for my car had the pinion centered. Same vibration!  But, I am going to carefully measure everything to see if some improvement could be made on my car.  I custom made my tranny crossmember and centered the tailshaft between the frame rails. Maybe that was wrong.
My rear axle currently in the car has the 5/16” pinion offset like stock. I need to measure everything and maybe I will need to reposition the crossmember sideways. As the article states, the car is not going to be happy unless it is RIGHT.   I know the vertical angles are correct. I just need to get the horizontal component dialed in.

This 5/16” offset of the pinion brings to mind that the Mustang rear ends are ALWAYS put into the car with the rearend offset to one side… by 5/16”!  You will discover this when installing larger rear tires and find that you have 5/16” more clearance on one side.  I wonder if that was Ford’s design to align the driveshaft.

Does anyone know if/how much classic Mustangs have the engine offset to the passenger side?   It seems that is the starting point to get this right.  I will find out when I start measuring.

Last edited by MS (10/07/2022 6:25 PM)

My Jag rear is smoooooth!!!!! I've only had it to 157 MPH though.

One time I mounted one of my wireless cameras under a car to chase a vibration. I started out with it mounted so I could see front to back sort of off to the side a little. I could see the length of the drive shaft and see a bit of the tranny tail housing. I sat in passenger seat and let son drive. It was scarry. The rear axle got real excited and the motion was not just up and down. There was enough force that the rear leaf springs were allowing the axle assembly to rotate back and forth around the axle centerline. Since then I have used the camera method a lot. A GoPro works good. I have also used my endoscope. One I did ended up being the engine mounts got in a rythum that put a force just wrong for the rear springs. New mounts fixed it.

I did the accelerometer thing once on my race car to find a vibration source. Worked great, but took a fair amount of high dollar equipment I had access to from work. Camera did same job a whole lot easier.

Are there any shops in your area, where you can take the car and put it on a dyno for them to source the vibration?

Chassis dyno sounds like a REALLY good step in the right direction !
6s6

MS wrote:

None that I know of around here. Maybe San Antonio or Austin

 
As many motors you build Steve, seems like you should buy one.

Bearing Bob wrote:

Steve, I can't remember if you've tried switching wheels, would be worth the time if you haven't.

Every mechanical part on the car has been changed to something else at least three times

red351 wrote:

I just seen something about what the color dots are there for on new tires. I have to pay more attention to them since I dismount & mount and balance my own. Just never knew that

Well, if that's true, the tire stores aren't following the "dot" theory....

I recently changed tires on my Pilot.  the circles were all right at the valve.  And my tire dealer has been there for a couple of generations.  Lots of experience.  The tires have virtually no weights on them.  Can't remember offhand what brand.