Flex Disc
 

Went to change the rear flex disc on 89 300TE took out all the bolts and then started to push the drive shaft forward to remove the old disc and notice a steel shaft coming out of the diff going into the drive shaft. How far forward can I push the drive shaft? Do I have to remove the shaft to remove the flex disc??

I'm pretty sure it's actually part of the driveshaft, not the diff. If you can't get enough of a push forward to disengage the dshaft from the diff, you'll need to frop the heatshield for the exhaust and remove the bolts for the center support, this should give enough of a change in angles to get the dshaft dropped.
Gilly

The steel pin you are seeing is part of the differential. There is also one on the back of the transmission. You will probably have to remove the exhaust system and heat shields to get to the center bearing. I have always had to loosten the big nut on the driveshaft, disconnect the center bearing and collapse the driveshaft at the center spline and then it will clear the offending pin.

Good luck its not easy.