Blue Square Electrical Control System
Gear Controller
Gearbox and final drive Controller
One was provided per cab.
Operation required a removable brass reversing lever - this has several different names such as 'golden handle' and 'spoon'. It is one of three items a driver required to bring to drive a Blue Square DMU, the others being the vacuum brake handle and the desk key.
The gear handle can not be turned unless the reversing lever was in the forward or reverse position.
Description
From the BUT 50000 Series Service Manual:
The gearbox controller is similar in construction to the throttle controller. There are two camshafts, one for the operattion of the gears in the epicyclic gearboxes and one to actuate the forward and reverse gears in the final drives. Each cam closes an electrical contact, thereby operating the appropriate E.P. valve, which in turn engages the selected gear.
Only when the forward and reverse lever is in the OFF position, can it be removed from the controller.
Schematic
As shown in the BUT 50000 series manual:
The top connection M+ goes to the "Relay Switch Panel", the feed activates the relays connecting the lamp circuits on the "Engine Control Panel", and M+ also goes to the two engine start buttons on the "Engine Control Panel".
L+ is circuit 33, the "Train +" circuit that goes through all vehicles. F and R are wires 28 and 28, which are the "Forward" and "Reverse" circuits that go through all vehicles.
The next two T5 and T6 go direct to the throttle controller, as does the bottom connection G+.
G1, G2, G3 and G4 are wires 19-22, circuits Gear 1-4 which go through all vehicles.
Exploded View
Taken from the AEC Spare Parts Catalogue.
The parts are identified in the three pages below, along with the AEC/BR/Sharps part numbers.
Overhaul
John Joyce has written an article on overhauling gear controllers.