Ok guys, I have my pinion angles get correctly, meaning that they are parallel (trans flange=+3 and rearend=-3). So if the pinion angle is set correctly what else could cause the driveshaft to vibrate? In 5th gear, in rpms between 2500 and 3000, I am getting a big whirring sound and some vibration. Any ideas? The sound goes away below 2500 in 5th and above 3000 in 5th. It doesn't make the sound or vibration in any other gear at any rpms. I'm puzzled over what the heck it could be...

 

I've read that several other people on some other boards have the same problems with the Denny's DS. A similar thing happened to me. I have a PH shaft, but when I installed the adapter plate, mine wasn't seated all of the way before tightening it down, which caused vibration. I couldn't get it out to re-seat it, so I used a block of wood and a hammer to lightly tap it all of the way in. It moved considerably when I started tapping it. I have no vibrations what so ever now.

One of the guys that has the vibrations (I think his were at 100MPH+) tried tapping his in and he said it definately got better, but hasn't gone away. Now, I think it starts vibrating around 115 or so.

Basically, I'd check the adapter plate installed in the rear flange, that seems to be the issue with the Denny's shaft based on what they are all saying.

 

Pinion angle does not cause vibration per se.

You might want to decrease the rear to two.

I like the suggestions above. If the mating flanges are not registered correctly it will cause you problems (also your angle readings will be thrown off). Then again, it could be the drive shaft is not properly balanced.