Hello all. This topic has been covered several times on the prune before but I can’t find it with the search engine so here goes.
On the 744 when the gear is selected up the gear doors open. When the gear doors are open a hydraulic sequence valve positioned by the right hand doors ports hydraulics to an actuator (de-spin actuator) which actuates the alternate brake metering valve in the r/h wheel well which is meant to stop the wheels spinning before the gear is swung into the wheel bay. The braking pressure on retraction is sufficient to stop the wheels turning within a revolution. I have seen this when trouble shooting the defect, white stripes were painted on the tyres and high speed film on take off.
Either the sequence valve or de-spin actuator is worn ( I can’t remember which) and insufficient pressure is supplied to stop the wheels turning before retraction which results in some fairly violent vibration being felt in the cabin. It has been happing since the first aircraft arrived and a “mod” program fixed the issue in early days but the aircraft are getting older and thing must be getting worn again.
This is the cause for the vibration on the 744, unnerving but no great drama
Hope this helps