There shouldn't be any need to replace the relief valves. If the motor worked before disassembly, it ought to work now.
Something was
probably assembled incorrectly. I have a used hydraulic gear pump, hoses, and assortment of fittings and adapters. I welded a small OD stub shaft onto the pump's input shaft, so I can drive it with a cordless drill. Whenever I get done putting a hydraulic motor back together, I always hook it up to my drill-driven pump to run it under no load.
The pump isn't anything fancy....just something like this:
It's easy to see if anything is dragging or not functioning the way it should because any backpressure at all will stall the 14.4 volt drill. If the motor was assembled correctly, it will spin smoothly without any skipping/jumping at all. It will also start from a dead-stop if the drill is spun
just fast enough to make the pump move oil. It's probably hard to visualize, but motors can even be compared side-by-side in this manner. One with more internal leakage, or a pitted roller or two will behave much differently than a motor in better shape.....and those differences won't be anywhere nearly as easy to see once the motors are back on the machine and being fed oil from a higher-volume pump that's driven by a 50 hp engine.
The biggest reason, (in my opinion anyway), to
not re-install a hydraulic drive motor without test running it, is because on any hydraulically-driven machine that has more than one drive motor, the *good* motor will try to push the machine along.....even if the *bad* motor is locked or partially locked. We have a LOT of machines with a hydraulic motor on each wheel. If one of the motors locks up, the others will still try to push it along, at least until something breaks internally. And when that happens, metal debris from the breakage is in the drive system. Unless all the lines/fittings/valves/motors are pulled and disassembled to clean out, there will be small bits of metal shrapnel in there to foul things up later on. You'd think that manufacturers would isolate motor shrapnel and contain it to the motor that failed by using screens on the individual motor ports....but hardly any of them do.
Attaching the drill-operated pump to a motor to run it takes only a couple of minutes per motor....and it saves a lot of potential headaches.
