Left rear wheel doesn't want to move...

[CudaDownUnder]

My 73 Cuda ( 340/727/8.75 ) has been sitting for a few weeks so I fired her up with the intention of driving it up and down the drive way. I selected drive while pressing on the brake. I released the brake and the car didn't move. I gave it some gas and the right rear tyre started the spin and slid the rear of the car to the right side  - kind of cool but not what I want to do in my narrow garage...

It seems that the left rear wheel didn't want to move. I turned the engine off and selected neutral. I pushed the car forward a few feet by myself and it all felt ok - no resistance. I jumped back in, fired her up, selected drive - same problem, right rear spins, left rear static. I selected reverse and it reversed ok. Selected drive again - no go, same problem. I jacked the rear of the car up (wheels off the ground) and selected drive - nothing happened , so I gave it some gas and the left rear started to turn. After a little more persuasion it seemed to be behaving so I dropped it back on its wheels and tried selecting drive again. It moved forward this time but I could hear a constant squeek coming from the left rear wheel while in motion. That's as far as I got.

What could be causing this? Diff centre? Axle bearing? Brake dragging?

Some extra info... the pinion seal on the diff leaks, not a lot but I suspect it's been leaking for a long time. The diff probably needs an oil top up. The rear park brake is disconnected - no cables. I haven't had the rear brake drums off yet - maybe tomorrow - too cold and dark now!

[Super Blue 72]

The left rear moves with the wheels in the air? 

How hard is it to turn the left rear wheel by hand when it's up in the air? 

My first inclination would be to say the brake is dragging.  You said there are no E-Brake cables?

I would pull the wheel and check the brake system in the left rear wheel first before opening up the differential.

[CudaDownUnder]

I jacked the rear up again and pulled the wheels off. I tried to remove the drums but neither of them would budge. I tried to undo the self adjusters but they wouldn't budge either (yeah, I moved the locking mechanism out of the way). After a lot of banging and cursing I managed to get the brake drums off and found that the automatic adjuster spring on the left side was snapped into two pieces. The adjuster screw assembly (star wheel) on both sides was ceased. I cleaned them up, greased them, and clipped it all back together after resurecting what was left of the adjuster spring.

I only managed to drive a few feet forward and backwards but it seems ok. I'll try and drive it tomorrow...

[Super Blue 72]

Sounds good!  Glad you found the problem!