we have schwing 61 m with pump kit p2525-120/85 rb.one of the deferential cylinder rod has been loosed from the piston.we replaced the two deferential cylinder with a new .now the pump will change over when the right cylinder is full extended while the other one when it is full extended it will not chang over.we doubt in one of the mps spool valves.it also will change over when it will run in the maxmum speed but when decreasing the pumping speed it will change over in the end of one stroke only

Did you offset the piston rings on the left cylinder.  I believe that you are bypassing some oil on the left cylinder which is causing you not to shift with a lower volume of oil.

we thought it will be something like that.after revising the hydraulic schematic drawing  we found that we fixed one of the reversing valve inside the mps in wrong coonnnection.we fixed zk1 instead of zk2 so it was logically that it will not work because one of them supply high pressure signal and the other one supply low pressure signal to the reversing valve spool to help the spool spring to return the spool to the natural position.

Shady

Dont worry about the piston rings not being offset, the amount of oil that is bypasssing, is nothing to worry about. You have a mps problem, it probably lies with the two check valves, which are screwed in on the long or top side of the mps. Interchange them, and see if the problem with the cylinder that is not shifting moves to the other cylinder. Since youre already working on the mps, make sure all the spools are moving freely, and double and triple check the plumbing.