Norfolk Garage

This month Richard Hall has mainly been dealing with transfer box problems from a 110 to Series III

The LT230 transfer box is one of the unsung heroes of Land Rover mechanical design. It first appeared in 1983 with the launch of the One Ten, found its way into Range Rover and Discovery models, and continued with only minor design changes until the final Defender rolled off the Solihull production line last year. It was simple, robust, easy to use and played a big part in giving the Defender 90 and 110 their astonishing off-road capability. However, it does have a couple of weaknesses (which also crop up fairly often in older LT230equipped Land Rovers).

The first – unsurprisingly for an old-school Solihull product – is a tendency to leak oil, usually from the same couple of places. The intermediate gear shaft locates in a hole machined right through the front face of the casing, and is sealed with a simple O-ring. This hardens and shrinks with age, resulting in oil running down the front face of the casing close to the join between the transfer box and main gearbox. To change this little seal (which costs pennies) the transfer box has to be split from the main gearbox and partly dismantled. Since the intermediate shaft sits above the oil level in the transfer box there is a limit to how bad this particular oil leak will become. For this reason I tend to advise customers to ignore it until the transmission has to come out for some other reason.

The other common fault causing these transfer boxes to plaster the owner’s newly-laid driveway with EP90 gear oil is failure of the oil seal behind the front output flange. The rear output flange, despite having a seal of identical design to the front, tends not to give too much trouble, but the front one is exposed to water, mud and salt spray in the winter, which does not do the sealing surface of the flange much good. Nine times out of ten, if there is oil leaking from the front flange seal you will need to change the flange assembly as well as the seal. It isn’t an especially difficult job, provided you can get the central nut undone – it’s a 30 mm AF whopper – and if you don’t need a big breaker bar to shift it, it wasn’t done up properly in the first place.

The result of all this is that I see a fair few old Defenders which come in for a service with little more than a teacup full of oil inside the transfer box. It is a tribute to the robustness of the basic design that the LT230 seems to put up with this kind of neglect quite happily. However, it has one other fault which no amount of topping up the oil level will protect against, and a couple of weeks ago I had a vehicle come in which reminded me (and its owner) quite sharply of the LT230’S most serious design defect.

The vehicle in question was an ex-military Defender 110, supplied to the Ministry of Defence in 1995 and one of the last 2.5 non-turbo vehicles to reach the Army before production switched to the 300Tdi-engined Wolf Defender. Ex-military vehicles are a bit of a mixed bag – some have had a very hard life, others appear to have been barely used at all. This particular example was somewhere in between, with 110,000 kilometres (around 69,000 miles) on the clock, very straight body panels and a general air of having been well cared for during its service life. The engine was a green-painted MOD reconditioned lump, but the gearbox and transfer box looked original and untouched – a bit mucky on the outside but tolerably leak-free, and both with serial numbers consistent with the age of the vehicle.

The brief was to replace the sluggish old 2.5 diesel with a 200Tdi from a Discovery, fit power steering and change the transfer box for a higher ratio one. Almost all ex-mod 110s have a 1.6:1 ratio transfer box which is great for pulling really heavy loads in hilly terrain, but somewhat undergeared for motorway use.

When someone asks me about fitting a Tdi engine to an ex-military 110 I always ask them what they intend to use the vehicle for and unless the answer is towing a fully-laden 3.5 tonne trailer on minor roads I usually recommend changing the transfer box, either for a civilian Defender box (1.410 ratio) or a Discovery 1.2 ratio unit. The latter is arguably a little overgeared for heavy towing or load carrying, and tends to blunt the acceleration a bit, but provides

comfortable and remarkably economical motorway cruising capability.

There is however a risk in changing the transfer box on a vehicle that appears to have nothing wrong with it, and this takes us straight to the LT230’S most serious design weakness: inadequate lubrication of the splines on the input gear. This gear transmits drive from the gearbox mainshaft to the transfer box. It is supported by taper roller bearings fore and aft, and is a simple splined sliding fit onto the gearbox mainshaft. It is a good, robust design, except that whoever was responsible for it failed to take account of the need to lubricate the splines. The gear sits well above the oil level in the transfer box, and although splash lubrication keeps the bearings rolling sweetly, there is absolutely no way that any oil can get into the centre of the gear where those splines are.

When building up new transmission assemblies, the factory applied grease to the splines. Unfortunately, the passage of time causes the grease to dry out, so it no longer keeps the splines sliding smoothly. With the gear being a free-sliding fit on the shaft there will always be a small amount of movement between the two, even when new. Once the grease dries, that movement will result in the splines on the gear and mainshaft wearing as they rub against each other. Tiny metal particles become embedded in the dried grease, turning it into a highly-effective grinding paste. As the splines wear the movement between them increases, which accelerates the wear still further. Eventually the splines wear so thin that they disintegrate (usually when pulling away from rest in first gear), there is a loud bang and all drive is lost.

The input gear in the transfer box is easy and cheap enough to replace, but the worn gearbox mainshaft will require almost total dismantling, and unless you already have the various special tools needed to do the job, you will be looking at a reconditioned gearbox. At some point in the mid 1990s Land Rover came up with an astonishingly simple fix for the problem. They drilled a large hole straight across the centre of the input gear, allowing oil to reach the splines. These cross-drilled gears are available as a replacement for the solid gear in all but the earliest LT230S, and most vehicles that have had a new gearbox in the last few years will have received a crossdrilled input gear at the same time. But there are still an awful lot of older Land Rovers running with the original solid gear, splines caked with dried crud and grinding themselves into oblivion with every gear change.

In my experience it normally takes at least 120,000 miles, and usually rather more, for the gearbox mainshaft splines to wear so badly that there is no point in fitting a new input gear over them. A small amount of spline wear (maybe 20 per cent of the total width of the splines) can be overlooked if you are on a restricted budget. But on a wellmaintained, lowish mileage vehicle I really wasn’t expecting trouble.

And that feeling of optimism lasted as long as it took for James (who I had entrusted with the job of removing the input gear from the old transfer box prior to separating the two halves of the transmission) to tell me that the input gear seemed to be stuck on the mainshaft and wouldn’t slide out. The only time I have had that happen is with splines so badly worn that the short unworn portion at the inner end of the gear gets out of line with what is left of the splines on the mainshaft and catches, preventing the gear from being withdrawn. And sure enough, after much waggling and levering, the input gear finally parted company with the mainshaft to reveal splines that were perhaps only one set of traffic lights away from failure.

So I rang the customer to give him the bad news, then ordered a replacement gearbox from Ashcroft. I was still a little puzzled that this particular transmission had worn so badly at a relatively low mileage. Separating the gearbox from the transfer box provided a possible explanation. Since the input gear is supported on bearings that are independent of the main gearbox, perfect alignment between the gearbox and transfer box is essential to avoid the mainshaft and bearings being subjected to side loadings which might cause damage.

Alignment is achieved via two steel dowels, a large hollow one at the top and a smaller solid dowel towards the bottom. On this particular transmission assembly, the large hollow dowel was missing. The input seal in the transfer box had obviously been replaced, as it was recessed into the casing rather than flush with it as it should have been.

So it would appear that someone had removed the transfer box (presumably during the vehicle’s Army days) and left out the dowel when putting it all back together. Did this contribute to the spline wear? I can’t be sure, but it seems likely.