Thanks JKH , trust me I have been grasping at straws for a while on this one... yes they are 2 stage telescopic . visibly I can see no damage to either jack although I haven't dropped lines and measured. I did check that there are no tight spots in the rails and rails are lubed up . when the fault occurs and it is at ground floor level the top of the first piston on the right is say 3 inches from the cylinder head and the one on the left is maybe 5 inches from the head..there is still clearance on the bolt heads going into the tops of the jacks so I discounted the car binding in the guides. the T joint is more or less in the middle and the unit has ran fine for 10 + years ( according to the client ). I have some cemco telescopic jobs ( different tho in that they are 3 stage direct single ) made by ALGI ..they have similar problems with say the second stage travelling too fast and causing 'bumping' at the bottom and it is down to the internal seals at the bottom of stages 2 and 3...( not easy to get now that cemco are no more) so I wondered if it may be a similar problem ? pulling pistons is a last resort tho'.
