Loud Bang and no drive (autobox)

[markatspace]

I have just had to recover my 230sl auto 1965.
I was driving it was changing up gears and there was a loud bang from underneath and then no Drive. The engine runs fine. Thinking its drive train I jacked the car up and had a look at the gearbox rubber coupling thinking it may have broken ( it looks in good condition) no other obvious problems are visable.
I run the car when jacked up, putting it in drive the wheels turn.
I have been suffering that the car jumps out of gear when the autobox is cold, I think thats because the gearlinkage is badly adjusted. This goes away when the engine is warm or you put a bit of pressure on the shifter (so I think this is an unrelated problem)   How to work out if its prop, Diff or gearbox?
Thanks

[Cees Klumper]

"I run the car when jacked up, putting it in drive the wheels turn."

I suppose from your report that the wheels do not turn when the car is on the ground. I would maybe, as the car is on jackstands in drive (engine off) try and move the wheels and see what happens, what resistance you feel and whether there are any obvious issues. Should be relatively straightforward to diagnose?

[merrill]

possibly a failed torque converter?

[markatspace]

Theres a noise as if something in the drive train is turning. but no drive.

[stickandrudderman]

If there are no externally visible defects to the propshaft then you have either diff/driveshaft failure or transmission failure.
Usually the load bang is associated with the former.
With the wheels off the ground chock one wheel and try to turn the other. If you can turn it easily but the propshaft is not moving then you definitely have diff or drive shaft failure.

[ja17]

Possibly the slip joint universal assembly in the swing axle failed. Sometimes the bolt securing it comes loose or the splined nose just snaps off!

[markatspace]

thats very helpful Colin. I will check tonight after work.

[markatspace]

I chock a rear wheel and the Prop turns ok.   There is a bit of backlash in the Diff 1/2" of wheel travel. I can hear oil moving in the gearbox.  When I repeat on the other side its the same. So guess its the auto gearbox. 
Before I drop the gearbox out of the car are there any tests I can do to be sure where the problem lies?   I dont want to rebuild the gearbox to find its the Prop shaft or Diff.
Is there anywhere in the NE of England that rebuilds classic mercedes auto gearboxes?

[rwmastel]

I chock a rear wheel and the Prop turns ok.

... are there any tests I can do to be sure where the problem lies?

I thought chocking the wheel so it won't move, and the main drive shaft does move, proves the problem is in the diff.  No?