This FV402 has a steering system that functions exactly the same as that in a T16. There is a Cletrac controlled differential with contracting band brakes running in oil in the central unit to provide the main steering function which when an outer steering lever is applied. this reduces the speed of one track and at the same time speeds up the other track by the same amount. A full application of one of these brakes will make one track go at about half the speed of the other with less difference / bigger radius of turn if you partially apply the brake.
Just inside the lower hull sides and mounted onto the final drive units are drum brakes with rod linkages to the stopping brake pedal and to the two central steering levers. Thus these brakes can be used either as the service brake (for slowing down / stopping) as a parking brake by pulling and latching the two centre steering levers, or for pivot turns in very confined situations by pulling just one centre steering lever.
Also inside the steering gearbox is the forward / reverse gearbox. This can only be changed with the vehicle stationary and the Wilson box in neutral. There is a neutral position in the F/R box but it is very unwise to try to engage F or R from N with the engine running - even with the Wilson box in neutral. There is too much drag in the Wildon box so the prop shaft etc will turn at about engine speed and the resultant grinding of gears in the F/R box is very destructive. Instead, stop, engage N in the Wilson box (or GC pedal to the floor which is what N position is) and smartly but not violently go straight from F to R or the other way. Do not pause in N or the propshaft will spin up.
The Wilson box contains 5 possible gears that can be engaged at any speed or load by pre selecting what you want next and then fully pressing and releasing the GC pedal. Do not use this as a clutch, but release it smartly in one movement. There is a fluid flywheel between the engine and Wilson box to cushion the drive and allow stopping in gear and progressive engement of the drive when starting off. When changing up or down match the engine revs to the next gear as you would with a manual box.
Unlike a T16 you are not supposed to use the Cletrac (outer steering levers) both together to stop the vehicle and there may well be an interlock to prevent you. This is a hangover from WW2 British tank designs as the Merrit Brown box in Cromwells etc would be damaged if you engaged both steering brakes.
This four lever system continued through the FV420 series into the pre production FV432s but then someone realised it was silly and production FV430 series got an ordinary Cletrac system with a more robust Cletrac controlled differential and no separate stopping brakes. This lasted untill modern civilian legislation required the FV430 series to be upgraded with a steering box that offered two separate braking systems.
David
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