Tobias,
Once again thank you for your help here. Your technical English is much better than my German or French so I am working just from the drawings and the important instruction not to press the button in any gear other than R or 1.
Malcolm,
As you say the "safety" clutch is only a torque limiter, though I am puzzled why they didn't use a fluid flywheel which was well established technology by then and would have been much nicer to drive.
To re-write my previous post in the light of the video and more from Tobias:
If no levers are pulled the drive goes to both tracks at exactly the same speed so the vehicle moves in a straight line.
If one lever is pulled all the way without pressing the button, the clutch inside the brake drum is released and the brake band nearest the centre of the vehicle tightened giving a lower ratio drive to that track. That side track then turns slower than the other which remains in high and the vehicle turns with apparently quite a large radius.
If one lever is pulled while pressing the button, the clutch is released as above but the middle brake band is applied which, if the lever is pulled hard, completely stops that track causing a pivot turn. It seems that doing this does not change the other track which therefore remains in high. This type of turn requires a lot of power and also tends to promote a skid on a hard surface rather than a turn, hence the instruction to only do it in 1 or R.
In both of these types of turn there must be a brief neutral (clutch released) before the brakes are applied or there will be excessive brake wear. However, in that neutral position the vehicle will turn the wrong way on a downhill slope as that track is no longer holding it back. This can be very dangerous and is a major reason why clutch and brake steering (which this is a form of) stopped being used as tanks became faster. Also the tendency to just skid in a straight line without actually turning can be quite exciting as I found out with a Valentine once. Adjustment is key here.
In theory, if you pulled one lever while pressing its button and the other without pressing its button, you would get a pivot turn towards the button pressed side, with the other track in low. This would be a bit more relaxed than having the driving track in high but would require a lot more training to get right in a tight spot so I suspect was discouraged.
Controlled differentials are SOoooo much easier !
David
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