Yanmar vio35-2 has a weak swing and drifts to the right. All the other functions are working well and have good power and digs good. Would it be the swing motor failing or a weak hydraulic pump? Where to start trouble shooting.
I would suggest inspecting the swing motor first as there should not be any drift and the park brake should lock the motor in position when no functions are activated. If you have a dozer blade option that has slow cycle times and also weak to power down then the rear gear pump may possibly need further inspection as well. Kind regards
If it drifts only to one side it might be the relief valves. Can you measure the pressure of the reliefs? I do believe there should be ports on the brake valve for it, and later compare the results to the factory setting. Also is the power of slewing/ swinging the same in both directions, or is it weaker to the right where it drifts?