There have been cases where the lower arms get lifted up and the rod and piston separate in the large lift cylinder under the seat. I’ll look and see if I can locate a thread. That sounds like your problem to me.
(Sorry could not locate the previous threads)
After everything, I believe Russell is correct.
I too recall a post by NIW where he provided a cross section of the L345's rear casting and explained how if the casting were damaged the piston push rod could drop out of contact with the piston. I cannot find the post but remember it well having experienced a similar failure on my Nuffield 465.
There is no mechanical connection between the push rod and the piston and this piece of casting is to prevent the push rod from dropping down out of contact with the piston.
On the Nuffield, the piston was connected to the push rod with a cotter pin which, after many years broke, I lifted the arms to connect an implement, the push rod dropped out of contact with the piston and the next time I raised the 3 pt, the push rod pushed out a section of the rear casting breaking it. Hence the bronze weld.
Disassembly is needed and then a method found to keep the push rod up. The repair would depend upon the interior condition of the casting. Avoid using the 3 pt control as you really don't know what is pushing on what and the forces involved can break most things easily.
If the inside of the rear casting is damaged, lifting the lift arms by hand could cause the push rod to loose contact with the piston as could a large bump.
Dave
