We have restored a 1998 - 763 and have an issue with the hydrostatic system. During restoration we rebuilt the drive motors. The gerollers looked good - no scratches at all and reasonably tight. However, it has low power on the left side. I've bought a guage and will pressure test both pump for reference. I'm assuming we will have to rebuild the hydrostatic pumps. My question is do I have to replace all of the pistons and swash plate if I find a worn piston? Or can I find just single pistons for sale? So far my internet serach only shows complete kits. I'm just trying to save the money and not replace good parts. Has anyone done this before. Thanks
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You won't get just a piston, it's sold as an either rotating group, the price isn't silly from loader parts source.
It's likely wear in the wear plate, a sheet of glass and wet and dry sand paper should be able to remove the scratches that are likely there causing your issue.
It's likely wear in the wear plate, a sheet of glass and wet and dry sand paper should be able to remove the scratches that are likely there causing your issue.
Here's some great news on this machine. We pulled the motor/pump assembly and both drive motors. We disassembled the the hydrostatic pumps and they look very good. The information I found said to look for deep scratches in the wear plates and pistons. We didn't see or feel anything that looked like a deep scratch. So we ordered gaskets and have put them back together. Next we connected the hydraulic lines to the drive motors and the outside pump to the inlet on the hydrostatic pumps. Then added the hydraulic reservoir fed into the outside pump. We also put a tee, ball valve and gauge on one of the hoses. One one pump/motor we get 3000 psi + and the motor runs and see a small leak coming from the shaft area. On the other side we get 2000 psi and a massive leak around the motor shaft. We also found some of the clamping bolts had backed out (that's the problem we think) We now assume this is the problem and have purchased a new drive motor rebuild kit. The orings looked ok but it's too much work to get to this point to go forward without resealing the drive motor. I have to assume that some leaking would be normal. 3000 psi through only a rotating rubber seal - I expect some leaking and think it should flow back through the case drain. I'm working on a video to post to Youtube and will share in a few days/weeks.
River Fluid Power
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You actually can get just the pistons without buying the entire rotating group. It's just that not every company is willing to sell them that way.You won't get just a piston, it's sold as an either rotating group, the price isn't silly from loader parts source.
It's likely wear in the wear plate, a sheet of glass and wet and dry sand paper should be able to remove the scratches that are likely there causing your issue.
Here's the final report on this. Thanks to all who looked and added to the discussion.
We resealed the drive motor that had a leak where the shaft fits. That did not fix it. It still leaked too much fluid.
I followed that by disassembling again. Prepping all mating surfaces using 220 grit emery paper on a granite surface. Took a dremel tool with a small sanding drum to the edges of all the housings where they had some rust bleeding into the edge. Replaced the small (about 1" oring that came in the kit from Loader Parts Source) oring in the first plate (the one with the shuttle valve) with a slight larger Oring since it didn't appear to fill the groove. Closed it back up and torqued per the maual. Wallah....no leaks. Why do I think this worked? 1) the oring that I found a substitute for did not look large enough. I couldn't tell using dial calipers if it was going to compress in the groove 2) flattening using emery cloth on the granite table. (I verified that I could see sanding marks at all edges and believed at that point I was flat. This wasn't much sanding - maybe 50 strokes on each mating surface. 3) I double the dremel sanding changed anything this was all done on the outside edge and that is not where the leak was.
We resealed the drive motor that had a leak where the shaft fits. That did not fix it. It still leaked too much fluid.
I followed that by disassembling again. Prepping all mating surfaces using 220 grit emery paper on a granite surface. Took a dremel tool with a small sanding drum to the edges of all the housings where they had some rust bleeding into the edge. Replaced the small (about 1" oring that came in the kit from Loader Parts Source) oring in the first plate (the one with the shuttle valve) with a slight larger Oring since it didn't appear to fill the groove. Closed it back up and torqued per the maual. Wallah....no leaks. Why do I think this worked? 1) the oring that I found a substitute for did not look large enough. I couldn't tell using dial calipers if it was going to compress in the groove 2) flattening using emery cloth on the granite table. (I verified that I could see sanding marks at all edges and believed at that point I was flat. This wasn't much sanding - maybe 50 strokes on each mating surface. 3) I double the dremel sanding changed anything this was all done on the outside edge and that is not where the leak was.