[45jim]

Malcolm, don't worry about offending I'm not a millennial!

I understand the system well and to be clear you must separate braking action and differential action to understand for it is not gears that steer the vehicle, its the drivers manipulation of the steering brakes and the resultant action of the differential which causes a change in direction.

The differential located in a tank behaves in a similar manner to one in the rear of a car except while the one in the car responds to friction generated between the tires and the road the controlled differential responds to driver induced braking action on the steering brakes.

The very reason brake bands are used in this application is because the drum must be slowed to a stop. The brake bands exert friction on the drum surface causing it to slow and then stop. This means that for a period of time the bands are slipping over the surface of the drum providing increasing amounts of friction until the drum is stopped. Just like the brake on a car, it is braking not "locking".

And if you notice on the Sherman the tiller bars (steering levers) have a significant range of motion. We all know from driving tracked vehicles that the turn starts after the free play is taken up (when the brakes first touch the drum) and gradually as we continue to pull back on the bar the turn sharpens. So, from the point that the free play is taken up until the bar is pulled back as far as possible the brake bands are in contact with the drum.

If one were to continue with minimal pressure on the lever a very gentle turn indeed would be produced and at no time would the drum stop and the brake bands would continue to slip, eventually glaze up and the heat could damage the drum. I believe this is Rob was speaking about. Correcting for the road crown with continuous "left stick" is to be avoided. This is I am sure where jdmcm's concern comes from.

If the tiller bars fully to the rear represents "full on" then every position forward (minus the free play) is one where the brake bands are in contact with the drum but with less pressure (and less braking action). Just like the foot brake in a car the lever motion is directly related to the amount of braking.

The amount of braking (which is variable) is directly related to how much torque is split between the output shafts. This means the torque split is infinitely variable starting from when the brakes start slowing the drum and increasing until the drum is fully stopped. Lots of brake band slipping.



As to how the British Army teaches their drivers I think my comments of:

At no time should a driver of any tracked vehicle (with a controlled differential) make "choppy" movements of the tiller bars to steer the vehicle. Smooth applications of the required force that result in gradual loading of the brakes are the most efficient. Sharper turns require more force and consequently more throttle - but smoothly.

firm and smooth applications of the steering brakes is the only way to drive

is pretty close to:

"To make a turn do it with several short smooth pulls instead of one long pull or a series of quick jerks"

I might not to be to eager to agree with the "several" aspect but its like picking fly shit out of pepper. Perhaps Rob got it just right with "a series of smooth applications"

Pretty sure I didn't break any of the laws of thermodynamics in my comments. The Sherman's friction brakes do more than just steer and when they wear out they are replaced just like any other wearing part. I have only seen the diff damaged by the lack of oil, and that was failure of a gear set not the brake linings or drum. They are after all, friction brakes!