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Sundstrand Pumps

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Just some information. I have been told, and understood, that the Sundstrand pumps on the Sovereign and Sunstar are the same. I know they have very different transaxles, but I am speaking of the pumps. I do think they are the same series, a Series 15. However, with attempting to correct the power steering issue on my Sovereign, I was going to change out the pump from another donor Sovereign. It has been said that there are different charge pumps on the units, 3 different possibilities on the Series 15 pumps. Well here is some more information, verified by actually looking at the charge pumps.

I had recently gotten a Sunstar with a bad engine, the PO also inlcuded a Sundstrand pump he had taken apart and then replaced with a different pump on the Sunstar. So I had this box of parts and I got to thinking, if there are different charge pump sizes and the pumps are the same between tractor models, then perhaps this pump will be one of the "bigger" ones as it was on the larger Sunstar and could require more pressure and volume. So I inspected the numbers on the charge pump housings. They were different. The Sunstar casting had W1 and the regular non power steering or even hydraulic lift donor pump had W6. I pulled them apart and inspected. The W1 pump has a significantly thicker gearotor; almost twice as thick. They both have the same diameter and fit into either housing, but the Sunstar pump would appear to have a much larger gearotor. Great! I will just swap them out. Not so. The shaft diameter of the two pumps is slightly different, the Sunstar pump having a larger diameter shaft that the gearotor would ride on. Different inside bores on the internal rotor. So I went and checked the suspect pump on the PS Sovereign. It is stamped W1, but upon inspection, it has a the smaller gearotor setup.

Therefore, the pumps may be of the same series, but they are definitively different, likely in more ways than just shaft size and gearotor setup. I learn something new every day.

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