There are several good articles on the Internet about this job, but as someone who has just done it, here are some hints not generally covered elsewhere:
The symptom is usually a loud banging noise occurring under load – meaning when taking off and/or climbing a hill etc. It is cause by a worn drive chain that is slipping – best to fix it before it gets worse.
The chain itself can be replaced, but it is expensive, the case has to come out of the vehicle anyway and the replacement of the chain can take several hours – not including the removal and replacement of the case. Good second hand units can be found at reasonable prices – contact Graeme Cooper Automotive or another specialist Land Rover service specialist in your area.
Be warned – This is generally NOT a job you can do without a vehicle hoist, also a engine/gearbox lifting jack and a lot of patience.
Get the new case before you start removing anything on the vehicle. Make sure you get new seals and prop-shaft bolt and nuts, gear oil and silicone sealant.
With the vehicle on the hoist. drain the oil (do NOT lose the plugs – you will probably need them for the replacement case), remove both prop shafts. For this you need a pair of open ended spanners for each bolt. It is a nasty job because of the difficulty of getting the spanners onto the nuts.
Remove the transmission brake cable, speedometer cable, the sensor plug, the “fore and aft” metal stay and tape these out of the way. Remove the brake drum.
Support the gearbox (not the transfer case) on the lifting jack. Remove all of the bolts securing the transfer case to the gearbox. The top one is actually a stud and does not need to be removed – the case will slide off it.
Unbolt and remove the two gearbox mounts. Move the cross member under the gearbox (the tubular one with flanges at each end) out of the way by removing the four mounting bolts and hammering the unit downwards to provide as much space as possible between it and the transfer case, but do NOT remove it completely, because you may never get it back in. Most likely it will be jammed tight between the chassis side rails). It should NOT be necessary to remove the exhaust pipes.
With the jack, lower the rear end of the gearbox and transfer case and pull it downwards and backwards to clear the drive shaft, then remove it from the vehicle.
Sit the replacement case next to the old one in precisely the same alignment so you can see what has to come off one and be fitted to the other.Clean up the main flange and smear it with silicone gasket material
Replacement is essentially the reverse of the removal, Probably the hardest part is aligning the drive shaft Do NOT forget to refill the oil – keep going until it reaches the upper hole then tighten the two plugs
Sounds easy? Like most other jobs of this kind, it is easier when you have done several already.