88'T-Bird rearend question

i just bought a 88' T-Bird w/ worked 5.0 & P225x60R16 tires on all 4. everytime i burnout i left 2 lines. So i put bigger tires on the rear 245x50R16ZR goodyear GS-C. today i did a burnout and only the right tire left a mark. it sounds fine i dont think its broke. prior to doing it when the back was jacked up i turn one rear wheel and they both turned in the same direction. i was pumped i thought i had a posi.any help out there i know thes cars are similer to mustangs. is bad,on its way or is this normal

If both tires spin the same direction, you have posi. The question now is, how strong are the clutches in your rearend and how worn are the cones?? They may be worn bad enough that the extra torque required to spin the bigger tires is making the clutches slip and now it reacts like an open rear end.

thankyou i kinda thought that but you comfirmed it so there is clutchs and they can be worn

Of course, with my other "Bird" there is enough torque that both tires spin with an open rear end....