Strange transmission problem

Hi, I have this problem with my 90 which feels much like the diff lock seems to engage and disengage on its own. I'm wondering if the centre diff is about to fail? It happened over a couple of days after which i removed the front prop shaft so I could use it to get to work as didn't want to damage the transmission. It drives fine now. The problem seems to be apparent during coasting at lower speed where the transmission vibrates vigorously like transmission wind up - I have different size tyres front to rear which could add to the wind up I would expect when in diff lock. It lasts for a few seconds, then appears ok for a mile or so. When I got home I jacked one wheel off the ground and I can spin the wheel when out of diff lock with a slight resistance - if i engage difflock, I cannot rotate the wheel. The diff lock lever feels like its doing the right thing and is moving the lug on the gearbox case positively and isn't moving when driving along.

Any help in working out whats going on. Are there any adjustments to control the point of when the diff lock is engaged. Any pictures of how the diff lock works?

thanks

Hi take the round plate off from rear of transfer g box, remove the bearing retaining plate ! May be tight to pry off, then inspect rear taper bearing!! If its ok then use some grips and pull out the input gear assembly with its front bearing , check condition etc!!
If bearings are worn replace both!!
Also check condition of internal splines , you can cross drill the gear while its out !!
Grease it up and put it back !!
It's not uncommon for these bearings to fail causing a similar symptom!!
Good luck!

Thanks for that, I will have a look, I have quite a bit of transmission backlash so I'm expecting the splines to be not great here.
But if the problem was here, wouldn't it be apparent when going along in 2 wheel drive too?

A few more questions - the clicking noise you get when the diff lock lever moves from left to right - is that from inside the transfer box or the lever. I'm wondering if the spring inside the transfer box that should disengage the difflock is weak or broken allowing the selecter mechanism to move but not enough to put the diff light on?

Land Rover LT230 Transfer Box - Difflock Mechanism - YouTube

I guess the selecter maybe not sliding on the shaft so well and not returning correclty?

thanks

draining oil out of t/box and checking for debris may give you an idea os state of center diff, as will counter rotating both props at the same time feeling for play and notchyness ,(one front and rear wheel need jacking up )d/l switch if wound in too far can hamper selector ,which is connected to its shaft by a spring pusshing lever tensions spring which should the slide diff lock collar in/out as diff and front out put line up ,some diff lock / hi low levers have a flat detent spring which can click ,most dont (spring is the same one used in series 3rd/4th synchro units )if you have an eye bolt as pivot for diff lock linkage it can be adjusted in/out to tension spring toward lock or out

Thanks, looked at it last night. Drained the transfer box oil and it looked fine - some small metal dust on the drain plug but nothing major. Centre diff spins freely with no noises/grating. There is a bit of backlash in all the transmission generally. What can I check next?
One of the front swivel housings didn't have much oil in - not sure if that could be relevant.

I might put the front prob shaft back in and when it happens again when not in diff lock, stop and see if there is slack in the prop shafts ie not all bound up as if diff lock is on?

Perhaps disconnect the diff lock lever and get a spanner on it to make sure its fully over/disconnected but It looks like it is anyway.

thanks