Well, there’s no chance of me putting any of this into place for a very long time, but I have bought a Range Rover Classic Borg Warner transfer box and a Discovery 200Tdi ZF22 automatic gear box and associated parts for a retrofit to the 109. Both were very cheap and the ZF at least needs some attention, according to the seller, though I’m assured the BW is good. They’re in storage for me to collect at a convenient point.
The idea is to move the engine forwards and for the back end transmission to be mounted a little aft of where the back of the standard transmission ends as the Discovery/RRC transmission is a fair bit longer than the SIII, even with its overdrive.
The reasons for the change are several, but mainly the noise level reduction. Drive any of the RRCs or Discoverys and the difference in noise level is fantastic. Even the Defender, with less noise insulation than my 109, is considerably quieter when driving. I would also like to have a less worrisome drive and ownership; the SIII transmission has stood up well to the Tdi, contrary to early internet advice, with all the problems occurring while I had the overgeared 3.54 diffs, but the later transmission would allow higher speed cruising with lower revs, lower gear noise and much greater resilience and oil retention. I am also getting used to driving an automatic in Dubai, and though having disliked them previously, I am getting used to the ease of use (despite still disliking the slow reaction and performance losses).
I have seen write-ups of a couple of LT77/LT230 retrofits that I was highly impressed by (Ed Parrot and “DiscoMikey”), and will be copying some of their solutions, specifically the use of the red lever connection to the later transfer box (BW has no diff lock, so the yellow lever could be omitted or installed as a dummy) and retaining the original tunnel (and matting).
The reason for going with the BW unit instead of an LT230 is primarily the way it behaves on a snowy or part icy road – the 4wd is permanently locked, but with enough slip to prevent damage on tractive surfaces, so you get the best of both worlds with no need to engage and disengage a centre diff as you go from slippery to good surfaces. I really like that in my RRC in winter. It is also quieter than an LT230, being chain driven. Its down sides are that it is reputed to be less robust than the 230 and it causes faster tyre wear (roughly double the rate for the same tyres on my RRC as on my 109, which was almost always in 2wd) because of the way the axles wind up against each other in tight turns. In theory, the LT230 also has the advantage of allowing one to remove a broken rear half shaft or prop shaft and drive on the front axle with diff lock, while doing so with the BW could conceivably cause continuous slip that could damage the viscous unit (not cheap). However, I don’t think that slip is likely when driven conscientiously on the front axle only, and the chances of blowing the rear drive is very small, being a Salisbury axle.
If anyone has any experience or knowledge of such a mod, do be generous with the advice!