Hey there, so I've got a 91 Bronco, 351w, E4OD, BW1356, Double Cardan Driveshaft, Ford 8.8" w/3:55open.

I've been hunting a vibration in the drivetrain, it has vibrated since I purchased it, I have just about rebuilt the whole damn thing in doing so. Vibration is at highway speeds (65-up) and sometimes in the lower speed ranges (10-25). The vibration is felt throughout the entire body of the vehicle, enough on the hwy to vibrate my headlights and everything in the doors. But generally in town and up to 55mph it rides absolutely smooth.

Things I've done so far:
Replaced Transmission Mount.
Checked for play in Tcase Output Shaft Bearing.
Replaced all Driveshaft Ujoints.
Had Ujoint centering checked and Driveshaft Balanced.
Checked for play in Pinion Bearing.
Rebuilt Spider gear set.
Checked for play in Carrier Bearings and Ring/Pinion.
Replaced Wheel Bearings and Seals.
Rebuilt Rear Brake Assemblies.
Balanced and Rebalanced Tires.
Change to a set of tires I knew 100% didn't Vibrate. (Largest notice in change due to fact that I went from 31's-33's, thus lower the rotation speed of the drivetrain.)

All of these things lowered the feeling of vibration but it is still present.

Both the Tcase and the Differential have Circular Flange mounts. The Tcase flange has a drilled dimple in the surface as if weight was removed from that side at the factory.

My question Is, is it possible that the two flanges were balanced against each other at the factory? When I removed the driveshaft I marked where it was mounted, but it is possible the previous owner removed it and did not put it back in the factory mounted position on the flange thus throwing it out of phase even though the driveshaft is balanced and itself phased.

Any assistance would greatly appreciated as this has been driving me both broke and crazy for the last 2 months.

 

I can hear crickets chirping on this post!
I had a '94 F150 with the E4OD and BW1350 combo and it had a vibe at highway speeds too. I did many similar things to quiet it with no success. It finally reared it's ugly head as the trans puked oil all over the highway. I haven't dissected it yet but certain the bad vibe was something going bad inside the trans. Get it to a reputable transmission shop and see if they would have any ideas. I know it's not what you want to hear but I hope it helps.

 

Does the vibration go away if you turn off the over drive on the highway? Possibly torque convertor is letting go.

 

hows the rear pinion angle?