Sherman A4A2 diesel 2-3 shift problem

[David Herbert]

I am sorry Lynn but no, it does not function like the braked differential steering in a universal carrier.

If you make a full brake application of a Controlled Differential (Cletrac) system, and fully lock the brake drum from turning (no slipping), the output (pink) shaft on the braked side will rotate at about half the speed of the corresponding shaft on the unbraked side. This is caused by the difference in the gear ratios between the green/yellow and the pink/yellow gear sets and will be designed as a compromise between the very large radius turns needed at high road speeds and the small radius turns needed when manoevering. On M113 family and T16 carriers they gave themselves a bit more scope for having a large minimum turn radius on the controlled differential by having brakes on the output shafts for pivot turns as well. These ARE directly equivilent to the UC setup.

Thank you Malcolm for posting the nicely coloured in drawing, it makes this discussion much easier.

Lynn, the reason that modern tanks (anything after Valentine) do not have steering clutches / brakes like crawler tractors is that at anything over about 10 mph clutch and brake steering becomes very difficult to control, particularly downhill. In fact on a steep downhill the tank can turn the opposite way to that intended as soon as you release the steering clutch. That can be quite hard to predict and is quite exciting. Also with clutch and brake steering the net speed of the vehicle is reduced when steering which increases the likelyhood of the inside track just skidding and no turn resulting - I have done this with a Valentine on a road and was lucky not to cause any damage. A Sherman will go sideways if you steer too hard but at least it turns.

David

[45jim]

I am not an advocate of continuous light pressure on the tiller bars. Smooth but firm applications when needed. And indeed they aren't the most manoeuvrable at slow speed in tight spaces. The M113 was equipped with pivot steer for that very reason!

I found this video supposedly of a weasel controlled diff in action. Nice animation and for arguments sake mostly correct. The other one is listed as braked differential steering, less clear but neat nonetheless.

https://www.youtube.com/watch?v=gxfeXAi-C7k

https://www.youtube.com/watch?v=SqBQRS3J0yQ4