As with many things, preventionis better than cure; this applies particularly to the transfer box. 4WD tends to be used more often only in conjunction with the main gearbox, so lack of use can play its role in transfer box welfare. There is a need to check the oil level by removing the small screwed plug in the rear side of the transfer box (arrowed); oil should gradually leak out as a few drops if the transfer box is full. It is not uncommon for the oil seal to fail between the main gearbox and the transfer box (part No. 236305 - Series I-III) and this will cause the transfer box to overfill with oil. So, if oil floods out, then you can suspect that particular problem. This main shaft oil seal can be replaced without removing the main gearbox from the vehicle but this is not the easiest way of doing it. However, if no oil emerges when the oil level plug is removed, then you need to top up with EP90 oil via the filler plug on the top of the transfer box. If the transfer box is generally noisy then lack of oil is the first thing you should suspect.
Difficulty in engaging the transfer gears, or slipping out of low gear could simply be due to the rubber boot at the base of the selector lever not fitting correctly. So check this first. Otherwise check the selector spring (part No. 56102 - Series I-III) for weakness or damage; it is located at the top of the transfer box underneath the threaded plug that is next to the transfer box oil filler plug. If replacing this spring does not cure the problem of slipping out of low ratio gear then it could be there is too much endfloat in the intermediate gear. To check this, drain the oil from the transfer box and then remove the bottom transfer box cover. The intermdiate gear is the largest and consists of two cog wheels joined by an integral smooth shaft. The end float should be 0.004 to 0.008in (0.1 to 0.2mm). The end float is adjusted by adding shims but the transfer box has to be removed and stripped to do this.
If the transfer box is noisy in operation and the oil level is correct then the problem could be worn intermediate gear thrust washers. An inspection as for intermediate gear endfloat as detailed above may aid in this diagnosis. Once again, removal and strip down of the transfer box is necessary to replace the thrust washers (part No. 219469 for 1948-64 and 521328 for 1964-84).
Another possible source of noise from the transfer box is due a worn worm drive and pinion for the speedometer drive, but this is likley to be of lower sound intensity than an internal transfer box problem. This can be sorted out without removal of the transfer box.
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