Insane Hydraulics

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Closed Loop Pump Breakdown - the Part That Took an Impossible Path

I received an "antique" this week - a closed-loop transmission that still carried the original Hydromatik name tags. The A4VG was series 3.1 (!) and the A6VM was series 6.0. If you repair hydraulic pumps and motors I dare you to remember the last time you worked on one of these!

The motor/pump combination came in with the usual "it ran just fine until it stopped with a bang" complaint, and I believe I ran into one of the coolest failures I'd ever seen.

The first "surprise" came in the form of a "nail-like" object smashed (or should I say s-meshed?) in between the gears of the charge pump:

Not bad, right? Notice that this series doesn't use the wear plate under the charge pump yet - so the overhaul will have to include some serious machining and lapping of the end-plate.

I am no stranger to finding foreign objects inside of hydraulic components, but still - it looked pretty cool, and I even posted the pics on LinkedIn (by the way - feel free to connect) with a description that sounded like "Look - this pump sucked in a nail! How cool is that!".

What I didn't post on LinkedIn, however, was my next finding, because I did discover where the nail came from. As I removed the side cover (yes, you read this right - this A4VG series did have a side cover, almost like Danfoss series 90s), I saw that the L-shaped wire that is supposed to keep the swash-plate bearing in place was missing:

Imagine that! As you can see - the length seems to be matching exactly, and also the "nail" has the typical wear pattern that these wires develop on the end that goes into the hole in the swash-plate, which makes me sure the "nail" and the missing wire are the same thing:

What I find especially cool - to the point of being unbelievable, is the fact that when the wear groove on the wire end became so deep that it allowed the wire to rotate and "fall out" of the swash-pate, not only did it somehow find its way into the suction line of the charge pump, but it also did so before the swash-plate bearing had a chance to slip out and cause a "catastrophic failure of its own"!

The fact remains though - this did happen, apparently, and now I have to find out how such a large and not very "hose-passable" part found its way from a drain into a suction port so quickly.

I spoke to the owner and arranged for a visit to see how the lines are connected. Hopefully, I will have this mystery unraveled soon enough!