Problems with 4WD will be dealt with in 3 groups.
Difficult to select or de-select 4WD
The yellow selector knob mechanism can jam due to lack of lubrication, lack of use or incorrectly fitted parts. The pressure plate at the bottom of the yellow knob spring (two fixing screws) needs a sturdy base washer and the fixing screws need to be secure.
The internal selector rods could be sticking and the driver's side floor panel needs to be removed to inspect these from above (possible from below but less accessible). If there is limited movement then lubricsting the shafts with a little EP90 may help to free them up.
Possible mechnical failures are a seized locking pin (on the top of the output shaft housing) or a damaged selector spring(under a threaded plug on top of the transfer case housing) and workshop manual needs to be consulted to replace these, but it can be done without removing the seatbox.
Difficulty selecting low gearbox via the red lever is usually due to an incorrectly fitted rubber boot or some other restriction at floor level preventing the lever from reaching its correct position.
4WD not reaching the wheels
If freewheel hubs are fitted then first check that these are functioning correctly by selecting 4WD, jacking up each wheel is engaged in gear, as it should be(support the vehicle securley on axle stands first).
If freewheel hubs are fitted and are working correctly, or if they are not fitted, then the same test can be used to determine if an axle halfshaft is broken. In the case of rear halfshafts, select neutral and with a rear wheel jacked up (axle stands again) rotating the wheel by hand should turn the propshaft if the halfshaft is OK. Repaet for the other wheel.
A fairly simple test to check that 4WD is fully functioning is to pull out a rear halfshaft, select 4WD and see if the vehicle can move.
4WD jumping out
If the rubber boot at the base of the red lever is under compression then it may push the lever into neutral and disconnect 4WD. Embarrassingly annoying.
The selector spring accessed from the top of the transfer box may be weakened and allowing the selctor fork to slip out of location.
If the problem is only with low gear 4WD then it could be that there is too movement in the intermediate gear cog. The intermediate gear float can be checked by emptying the transfer box oil and removing the bottom cover plate. the intermeidate gear is the biggest gear visible and consists of two cogwheels connected by a smooth collar. the end float should be 0.004 - 0.008in ((0.1 - 0.2mm). The bad news is that the transferbox has to be removed and stripped to adjust the endfloat with shims.
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