Let me just clarify a few points with the gearboxes as best I can - and don't shoot the messenger, I got all this from Dave Ashcroft. I have just spent a day taking my gearbox down there and picking his brains.
Firstly I must say the setup at Ashcrofts is pretty impressive. I had a tour around the workshops and there were about 12 to 15 employees rebuilding gearboxes on 2 floors, a big operation. All they do is L/R boxes so are the experts in the field. Inventory was huge and they do there own lockers now. Dave was very helpful.
Regarding the torque converter, the uprated one they do for the diesel takes up the drive earlier and has less slip resulting in less heat generation. The engine runs at lower revs if you have got a nice torquey engine. It transfers the drive better so you do not rev past it. It doesn't change the lower gear shift points which is done by the ECU.
He made the point that most of the p38 and Disco TD5 gearboxes warranty failures that Ashcrofts see are due to the gearbox being "cooked". A typical scenario would be towing a heavy caravan up through the Alps on a hot day, 40 deg C, going 50 mph and the torque converter hasn't locked up. It is slipping all the time generating heat in the gearbox. This is like deja vue for me. We spent some time looking at my DSE gearbox cooling. I have the original cooler under the wing which has the later fan fitted - so L/R obviously knew there was a problem. He recommended a second cooler on the other side - which I am not going to do! but what I am doing is getting a boss welded onto the gearbox sump so I can fit a temperature gauge.
Regarding the gearboxes. Picture the gearbox in 4 sections. The bellhousing, the oil pump housing, the main gearbox housing containing the cogs and clutches and a tailend housing. It is the oil pump housing which is different in length for early and late HP24s. I was told the main case is the same length for all HP22 and HP24 boxes. The difference in length is accommodated for by using the appropriate tailend, so an early HP24 box with a diesel bellhousing and a diesel tailend will fit, or a later 065 box with just the diesel bellhousing.
All the later HP24 065 boxes have the stronger HP24 clutch packs and internals as standard. Mine was made for a 4.6 Thor engine.
Ashcrofts also offer another option of having a HP22 box fitted with the HP24 internals. Stage 1, I think is having the C1/C2 one way clutch and planetary gearset upgraded and stage2 is the A clutch as well.
I am also staying with the diesel gearbox ECU. They do offer a Compushift option which is very expensive. Anyone hacked into the ECU ? I know a couple of people who would be very interested.
Dave