Going back to the gearbox, and going on the advice that the problem may be electrical rather than mechanical, we removed the electrical components of the gearbox from D22 peace by peace to retro fit back onto D23.

So starting with the easiest...

First thing we done was remove the push button selector from D22 and fit it to D23. D23's gearbox done nothing...

Next we removed the Voith control unit aka "The Brain" in the cab from D22 and fitted this to D23. Again, nothing...

We then decided to try D22's main gearbox control cable which ran from the cab to the gearbox at the back. This cable followed a rather complex route amongst the chassis members and tangled alongside the main electrical loom. Not the easiest of jobs considering the lack of room under the bus and the 25 years of dirt and goodness knows what else that came tumbling down on top of me!

Eventually the cable was released, hooked it into D22's control unit - which was still in D23, and ran it down the side of the bus into D23's gearbox. We started D23 up again, and.... well, nothing...

While John was dithering away at the electrical board earlier, he traced wires running from the gearbox control unit back to four relays on the electrical board behind the drivers seat. So these were removed one by one and fitted to D23.

This did make a change - by the time we swapped the third relay, pressing a selector switch on the gearbox control activated two relays instead of just the one we had previously.

By this point, young Andy McCombie who was watching, commented that the Voith gearbox should be making a noise, even when in Neutral. And this was missing from D23. It was also noticed that despite D23's engine running for a while, the gearbox in D23 still felt cold.

D22 was hooked back up to it's gravity feed temporary diesel tank, started up - and indeed the Voith gearbox kicked into action despite not being engaged. (All the electrical components were connected in D23 - so this proved the gearbox should be spinning even though the electrics were not connected).

Hmmmm.....

At this point John Kennedy had an idea. We could push D22 right up close to D23, then take the main gearbox cable I had earlier removed from D22 and run it from D23's electrical system straight into D22's gearbox. If this works, D23's gearbox is mechanically faulty. If it doesn't work, D23's gearbox would be electrically faulty...

After a bit of Dominator pushing, D22 was navigated into position, and a physical connection was made between D22 and D23 by means of D22's gearbox control cable.

With both buses running, gear was engaged in D23 and D22 went into gear!. Good!! We had now proven that any electrical issues were now non existent. Possibly, the replacing of relays in D23 may have rectified any electrical problems the gearbox chaps had identified earlier in the morning.

Theory we now have is that the drive plate is faulty on D23. So now the fault has been pinpointed - it is intended to swap gearboxes between D22 and D23, hopefully mid week if I can manage to squeeze the day off work. Some pictures of this exciting breakthrough!