Were your tires still wet after burnout? Track? My Ram 1500 will go sideways on a wet road, if I give it too much gas when the traffic light turns green. 

On the street, not the track. My Dakota with limited slip does the same thing on wet pavement. So why does my T Bird do it on dry pavement?

Condition of tires-inflation? Road temperature? Probably a stretch, but you don't have an answer yet. 

Tires in excellent condition. 32-35 pounds. Air temperature around 80%. No idea about road temperature. 

On a flat road, street tires, they all pretty much move right in the rear if you’re spinning them hard. I think it’s the reaction to engine torque. But given yours is severe, and the other way, I’d be looking at the rear gears/traction loc. Might be worth a phone call to Randy’s Worldwide (used to be Randy’s ring and pinion). Tell them the problem and ask what to look for when you pull it, which is what I’m afraid you’re going to have to do.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

There is a test that in this case, might be worth doing. It's described in the 50"s and 60's shop manuals how to check the holding force along with the smoothness of the axle clutch pack: Raise only one wheel and with the transmission in neutral, there is a specified minimum torque as measured with a toque wrench to breakaway and rotate the free axle. It also should provide a feel of the clutches while slipping. Checking a 1959 shop manual, 200 lb. ft.  of torque is mentioned.  Personally I don't think I could pull 200 lbs but maybe a breaker bar and a cheater pipe would work? Hope this helps..................

64F100 57FAIRLANE500

Found the front spring clamp on the drivers side spring was unhooked and wedged between the spring and the frame. Fixed it and tried another burnout. Better but still wanting to fishtail at the end of first gear. Finally checked the black marks on the road. Both sides seemed to be equal which indicates that the traction loc is working. Pattern was dark on the outside edges and light in the middle which indicates low tire pressure. I was running around 32 psi. Re checked tire manufacturers recommendations and discovered they recommend 38 to 40 psi. Tried 38 psi and another burnout but still squirrely. Burnout pattern on the road a little better but still indicates low tire pressure. Will try more air pressure. In researching the factory tire pressure recommendations i realized that the tires are 7 years old which I had lost track of. Could that be the problem because the rubber is probably getting hard? Tires always inside and probably around a thousand miles. Diamondback radials. 

Normally tire pressure is lowered for better traction on the track. If you're running street tires, there's nothing to be gained by doing a burnout. 

Not trying to gain anything. Trying to figure out why it won’t go in a straight line on a hard launch. I’ve been doing hard launches with this car since I bought it in 1965. Used to launch it on the drag strip at 5,500 rpm’s with 6” recap slicks and it always went straight. 

Glad you found a suspended problem that fixed most of it. Better than a broken posi. Maybe it’s getting squirrelly because you’ve got a lot more torque and horsepower?

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ