Vibration Help!

[martZ]

I have a TKO-600 in my '66 El Camino. I have a vibration @ 70 mph and up. It vibrates in 4th & 5th gear so, it's not RPM related. It vibrates above 70 mph regardless if it's in neutral or if the clutch is engaged or not, on accel and decel. I even shut the motor off and I still have the vibes until it gets below 70. It's a low frequency drone noise that I can feel in the seat. I replaced the ring & pinion, all rear end bearings, axles and u-joints. I had the stock shortened drive shaft rebalanced. My pinion angles are parallel (engine/tranny 4 degrees down and pinion is 4 degrees up). In fact, I experimented with different pinion angles with no change. After combing through the Pro-Touring forum, I thought that I should order a new drive shaft from Inland Empire. I measured it according to their website directions. After installing my new 3.5" aluminum d/s and 1350 yoke, I still have the vibration. The new d/s is similar in length to my old one so, I was wondering if the length was too short. I attached a few pictures(the cars suspension is loaded). Inland said to disconnect the d/s and push it into the tranny until the seal compresses then pull it out 3/4" and measure the distance between the d/s and the u-bolt face of the pinion. I measured 3/8". Inland said that was acceptable, but 1 5/16" still shows on the yoke. I've read that 3/4" to 1" is ideal. Do you think the d/s needs to be lengthened? I've also checked runout of the axles which are both > .002". The pinion yoke is approx. .005" same for the slip yoke. I currently have the car on jack stands and it still vibrates when I reach 70 mph. Thanks for your help.

[Vegas69]

Looks like the driveshaft is to damn short to me. I thought .75 showing was the spec. Have to check my paperwork.