slight grunch on overrun 5th only

I have a K plate disco that has a slight grinching noise in 5th gear, only as the back lash is changing from pulling to over run, once in over run it is silent as it is when its pulling .. i can not make it do it in any other cog but 5th... it is only noticeable manly after towing hard on the motorway. its has clocked up 136k i have had since 106k and it is getting more noticeable as time goes on .. so as it time for a tidy up the truck and the box is being dropped for a clutch so is a good time to sort it out

So by the sound of my description does any body know what it may be?
I would have thought with it only do it 5th it may be not to difficult to pin point
i am guessing a bearing or a thrust race or something
thanks
Dave

PS the oil has been changed very regularly as the long term owner from 15k to 100k had a oil change fetish as i do and halved the service interval

worn transfer box, my old 110 used to do it quite badly but never when pulling or slowing down, just when I eased back on the throttle to cruise

landowner said:

worn transfer box, my old 110 used to do it quite badly but never when pulling or slowing down, just when I eased back on the throttle to cruise

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if was a worn transfer box, would it not do it in other gears? its definitely only in 5th ..their is nothing to indicate that any thing is worn nothing is sloppy and all oils come out clean

davev8 said:

if was a worn transfer box, would it not do it in other gears? its definitely only in 5th ..their is nothing to indicate that any thing is worn nothing is sloppy and all oils come out clean

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Possibly right, mine only did it when travelling fast, didn't do it round town

My LT77 is all kinds of noisy in 5th on overrun, kinda like a rump rump rump rump noise

Never established it, has been apart twice anorl, had 3 transfer cases in the vehicle since I first noticed it.

It'll be something worn for sure but...?