L48 front pump failure

[1compact]

I am helping out with an L48 with around 2300 hours that has failed 4 front main pumps over the last year and 300 or so hours of use. The first 3 lasted about 2 hours each. The driven gear in the main pump eats into its support bushings and into the housing, causing a loss of flow and pressure, especially when warm. It's a tandem pump made by Hitachi, and the P/S portion looks fine. Even the drive gear and shaft look OK in the main pump. The factory service manual pretty much just shows a direct pump test, which it fails now, but passed when the pump was new. Pressure is OK beyond the main relief when cold, but drops off when warm.
Not sure what else to test. Blockage? Overheated oil?
After the other failures, the tractor had lines flushed, new factory oil and factory filters. The last time the tractor got a new main relief valve and new couplers out to the backhoe. They were a potential source of restriction.
Even before this pump was pulled off, the machine seemed normal until it warmed up. The pressure and flow test pointed toward a bad pump, and removing it confirmed it.
Any ideas or anybody seen a pump look like this? A good Hitachi pump service center?
Thanks for any advice.

 

[1compact]

I have heard of another L48 that was blowing the seal out of the main pump input shaft. It is still being worked on, and the cause is yet unknown. It sounds like it could be a similar root problem to this one I am working on - relief valve or backpressure problem?
Any ideas? Thanks.

 

[birddogger]

Supply side restriction, crimped line or plugged filter causing pernicious cavitation. Just a wild axe guess mind you. That metal had to end up somewhere.

 

[1compact]

Tractor is still sitting - haven't come up with anything, and the owner doesn't want to drop almost a $1000 on a pump, just to ruin it again. A place called Atlantic Hydraulics was friendly and helpful with it. They are a Hitachi dealer - I tried them because the pump was made by Hitachi. I emailed them pics, and they were pretty sure it was a pressure side restriction that caused this pump to look the way it does. Obviously they can't tell me what the restriction is, but at least they took the time to do some rough diagnosis. They said to look at/replace all the relief valves - which there are I think a total of 6 in the system - the main, some on the backhoe, and another on the loader valve. All are part of this hydraulic loop. At some point, the reliefs will all get pulled and inspected for debris/rust/etc.. Hopefully something will not look right.