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Depending on the loader model, it's probably somewhere between a 12-17gpm pump. They're gear pumps, not much to rebuild there. If it's trashed, as Rick B posted, surpluscenter.com has suitable replacements.
Something to keep in mind is the flow rate at x rpm. So a pump that flows 17gpm at 4000rpm won't be of use to you for example. You want it down in the RPM range in which you operate the tractor.
/ Anyone know a good hydraulic loader pump rebuilder???
I had a pump go out on m Case Dozer. Case wanted $25,000 for a replacement. They do not rebuild them, and they where not very helpful on my options. I went to m New Holland dealer for something else and asked them what I should do, he said that they send all their pumps to a place an hour away. I contacted them and they said that they would rebuild it, but couldn't say how much. It ended up costing me $3,500 for the rebuild. They where able to find most of the parts that they needed, but some of them they had to fabricate in their machine shop.
I would talk to the guys in the Parts department at a few different dealerships in your area, and ask them where they send their pumps. I've learned that they all send stuff out to a specialty shop to do the work. But you have to talk to them face to face. A phone call never seems to have the same results.