I recently swapped a 5.0 EFI and AOD into my 66 F-100 and ever since I have had this vibration at about 30 mph. I had the driveshaft balanced and the wheels have been balanced. I even had the front end aligned just to be sure, but it is still there. Any ideas?
Thanks Matt

 

Try re-phasing you drive shaft. Pull it off the rearend and turn it 180 degrees. Or double check to make sure you have the u-joints centered in the pinion.

 

Dittos on the driveshaft at the rear end.

 

if the driveshaft was just balanced it wont matter which way it is installed. that only matters if you reinstall the same driveshaft without balancing it.which is why you have to mark the relation at the rear end. i would check the ujoint caps at the rear. make sure they are centered i the yoke. also check pinion angle. i assume the AOD was longer than the trans it replaced. which could put your driveshaft at too much of an angle especially if you have a shortbed. also make sure the trans is mounted in a straight line with the rear end. if it is cocked to one side, you could have a vibretion. also check suspension mounting points- bushings good? shocks good? was the trans rebuilt? is t doin it at a certain RPM or in only 1 gear?
just some thoughts
hope it helps
matt

 

You are assuming that the shaft was balanced properly but a weight could have fallen off at some time since installation.
A sure fire way to eliminate the driveshaft as the source of the wobble is to do the following. Please be advised: I only recommend this and all safety procedures must be followed!

1. Raise the rear of the vehicle and place jackstands under the rear axle next to the spring perches. Place chocks in front and behind the front wheels.
2. Locate a steady item like a cider block, slide it under the truck near the drive shaft. Have a yellow or white crayon/marker handy.
3. Instruct your helper to sit in the vehicle at all times during the following procedure.
4. Start the truck with foot brake applied, and shift (auto=drive, manual, easy into first) into gear.
5. With the wheels turning at idle, roll under truck with crayon in hand, place block near shaft so you can hold marker firmly to block while just barely moving the marker toward the shaft.
6. Once contact is made, the shaft should have a solid stripe all the way around it. If not, you need to rechack the installation as mentioned.
7. Now have the helper ease the engine up to 30 mph and repeat the process except this time, move the marker forward or back just a bit to create another line. If the shaft is out of round, you will only get a partial marking on the heavy side.

Again, make sure you follow the safety items before and during.