[b3lha]

Originally Posted by svxistentialist

If I want to change the final drive in my VTD, I am presuming I have to fit a rear 4.444 diff say. To match this in the front I'm presuming I will have to change one of the pinions in the front diff to give the same 4.444 output ratio, so that the front and back axles are matched.

Yes.

Originally Posted by svxistentialist

Assuming I am correct so far, and knowing the front and rear sensors are both inside the gearbox, then I would deduce that both sensors are "seeing" equivalent revolutions, and therefore would send matched speed signals to the TCU.

Yes. On a Euro/Aussie VTD box with both sensors internal.

Originally Posted by svxistentialist

However I would expect the clock to be reading fast by a big percentage in this case. To make the clock [speedo] read correctly I imagine it would be necessary to give the TCU a new constant for multiplying out the speed.

Probably. My description above relates to sensor 1 on a USDM ACT4 box. But you are asking about sensor 2 on a UK VTD box. I will investigate how it works and get back to you.