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Discussion Starter · #1 · (Edited)
Good Evening,

I am hoping some of you out here have a decent amount of experience with hydro gear piston pumps. I have a good working knowledge of mechanical items and precision measurement, grinding, visual inspection, etc ( I work in a tool and die shop). But I haven't figured out these pumps completely.

I purchased an older Exmark Lazer Z that had hydro issues. Kawasaki engine runs great, blades run great, mower would not move. Once I got it to my shop I removed the pumps, wheel motors, all hydro lines. I cleaned everything including hoses, resevoir etc over the winter. I am confident I got all metal shavings out of the system. Pulled the pumps apart and installed new cylinder blocks and gaskets. Everything else in the pumps looked clean (seals, auxilary pump). Pulled wheel motors apart and cleaned. Reassembled and refilled with Exmark hydro oil (that stuff is expensive). Went through bleeding procedure.
Driver's side worked great, but passenger side hardly has any power. Last week I made up a hydraulic Tee and measured the pressure on each side under full load. The passenger side only builds to 500 psi making me think the pump is still not right. The driver's side (good pump) spikes up to almost 2500 - 3000 psi. Assuming the new cylinder block is fine, I wonder if one of the limit valves is stuck in that pump or I reassembled it incorrectly.

Doing the pressure test up on jack stands, I did notice something interesting. The driver's side (good pump) is difficult to spin the tire by hand, you have to slowly force it around. The passenger side is not like that it spins real easy with little resistance.

And the bypass valves are closed completely.

Figured I would ask for some input before pulling it out again.
Pump model is PL-B6AC-DY1X

thanks in advance.
 

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Gallagher, seeing you've had no replies I thought I would jump in with nothing but empathy, sorry my knowlege is next to nothing. I'm trying to learn about them too. I just bought a Dixon ZTR with separate units. Not having any problems but I know that sooner or later I will. My total sum of experience with hydrostatic drives is limited to dissecting and repairing a hydro transaxle years ago. I saw that it had a part resembling a helicopter swash plate. Years later I discovered that's exactly what the thing's called.
If one side's easier to turn by hand something's leaking inside but you already know that. I wish you luck. Post back with whatever you find so I'll remember it whenever I have to tear mine apart sooner or later.
 

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easy turning wheels

I have a Hustler Super Z. Wheel motor replaced a year ago. Gradually less and less power from side I replaced the motor. I also jacked up the rear and had a lot of resistance turning the good wheel. Hardly any resistance on the bad wheel. Opened up the pump and found metal inside that damaged the valve plate, cylinder block (non piston side), variable swash plate and the bearings. Does this help? I can provide part numbers for the pump and internal parts I ordered if yo want them.
 
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