Mercedes vario 814da 4x4

[part time nomad]

I have a vibration in top gear at about 50mph it seems to be coming from the transmission, if I am pulling (throttle down) it’s ok ,or throttle up on overrun it’s ok just happens when throttle is feathered, between on or off.
I replaced the transfer box and removed and checked all prop UJs
Also dropped some oil from all diffs & gearbox (no sign of problems)
Any ideas?

 

[Geo.Lander]

have you checked you prop shaft yokes are in phase?

 

[part time nomad]

Yes, all ok. The noise is a kind of gear chatter!
Only seems to happen in top gear. Say on a motorway or good road, you can drive round it but it annoys me.
I am thinking of taking a prop shaft off and driving it in central diff lock to eradicate front or rear diffs , but not sure if I will over heat the central diff spider?
Ps it only happens after it warms up.