Nick's Land Rover - Series III Rebuild

The swap to later axles is raising the diff ratios from 4.71: to 3.54:1.  It would be quite possible to fit the 4.71 crown wheels and pinions from the SIII axles to the new units, but since the Tdi should cope with the 35% gearing increase fairly easily, I have chosen to benefit from the increased speed, decrease in engine and transmission noise and increase fuel economy on the road – the standard gearing is a little too low, even with the Roverdrive engaged.  The speedo will need recalibrating, but there are plenty of companies to do that.

Ideally, I’d use 4.1:1 diffs (KAM Diffs sell the crown and pinions for the Rover axle, and Dana crown and pinion gears are freely available in the US for the Salisbury diff, if you can get them shipped), but that would cost about £500 in parts alone.  I’ll see how I get on with the existing 3.54s, and if they’re too tall, I’ll get the 4.1s later.

That leaves one problem – changing the diffs raises the high ratio gearing, which is fine on road, but also raises the low ratio gearing, which is a big problem off road for torque, low speed crawling and engine braking on hill descents.  The fix is to use SII Suffix B transfer box low ratio gears, with their 2.81:1 ratio.  Suffix C and all later Series transfer boxes (except V8 and 1-ton models) use 2.35:1 gears.  These Suffix B gears are a direct swap for the later transfer box main shaft low gear wheel and intermediate gear cluster.  The Suffix A gears use the same ratio, but the intermediate cluster’s internal diameter is much smaller, so don’t get that one by mistake.

The gearing reduction will offset most of the increase of the 3.54 diffs, though not quite all of it.  With 4.1 diffs, the low range would actually end up lower than on a standard SIII, so the final gearing would give the best of both worlds – about 17-18% higher in “high” (ignoring the overdrive, which gives a further 28%), and lower in “low”.

At the moment, I’m just getting the parts; I don’t need to fit them until the axles are installed, but I don’t want to leave ordering them until later for fear of them becoming unobtainable – the limited number of Suffix B SII boxes built means that supply of these gears is probably rather limited too.  I got the intermediate cluster from PA Blanchard for £50 and the main shaft gear from DLR for £30, both Genuine Parts.  These were the cheapest genuine prices I could find.

Axles, Gearbox

---