The two things that will wear out a Sundstrand are high hydro pressures, and dirty fluid that doesn't plug the filter. Both will show as a gradual reduction of performance.
A plugged filter will cause a similar lack of performance to what you report, and it will be accompanied by high fluid temperatures. I don't think that that is you issue, but if the filter has not been changed in the past 200-300 hours, now would be a good time.
The two things to check when one of these hydros suddenly goes south is the drive function (you've done that) and the implement lift/power steering (which you haven't done).
The hydro drive function can fail due to the roll pins holding the swash plate to the swash plate trunnion working their way out of position. This is a take-the-hydro-apart fix, but it isn't expensive (a pair of 1/4"x5/8" spring or roll pins).
The implement lift function can fail if the charge pump drive pin fails. This will also take out the hydro drive function. This is a much easier repair (you only need to remove the charge pump housing), and also an inexpensive repair (one needle bearing 1/8" diameter x about 7/8" long).
The fact that you heard a loud metal bang when things went south indicates to me that something mechanical has failed either in the drive line (your inspection found no faults), or inside the final drive (rear end). If it's inside the final drive, shavings from the damage may plug the filter and cause the symptom noted above.
Note that damage can happen to some final drives that can still allow the tractor to operate normally for several hours before the filter plugs with debris. It's only when the grinding of the case gets loud enough to notice that it is realized that a failure has happened. On my GT, that was after a whole winter's snow removal, about 60-80 hours. Preliminary indications of how bad the failure was, was the shiny silver specs in the fluid as it drained out of the case. In my case, I didn't hear a bang when the bolts holding the differential carrier together broke, but a review of the tasks done over the previous months pinpointed when it occurred. My fault. The Sundstrand hydro is considerably stronger than the final drive and the GT was overloaded with ballast.
Go thru all of the linkages again, both hydro and brakes, and check for wear or damage. On the opposite side of the hydro from the drive control is a stub shaft that is almost flush with the housing. It is the other half of the trunnion shaft holding the swash plate and must move exactly like the control side. No slop allowed. If it moves correctly, the 1/4"x5/8" pins are in place and the problem is elsewhere.
If I recall correctly, there is also a shock absorber involved that can cause problems with the linkage and/or drive function.
The only problem with overfilling the hydro is that the fluid will spill out the vent when it warms up and will need to be cleaned up. If it is low, the drive will be jerky, or non-functional if the tractor is nose high as in climbing a slope. If it too low, none of the hydraulics will work.
A plugged filter will cause a similar lack of performance to what you report, and it will be accompanied by high fluid temperatures. I don't think that that is you issue, but if the filter has not been changed in the past 200-300 hours, now would be a good time.
The two things to check when one of these hydros suddenly goes south is the drive function (you've done that) and the implement lift/power steering (which you haven't done).
The hydro drive function can fail due to the roll pins holding the swash plate to the swash plate trunnion working their way out of position. This is a take-the-hydro-apart fix, but it isn't expensive (a pair of 1/4"x5/8" spring or roll pins).
The implement lift function can fail if the charge pump drive pin fails. This will also take out the hydro drive function. This is a much easier repair (you only need to remove the charge pump housing), and also an inexpensive repair (one needle bearing 1/8" diameter x about 7/8" long).
The fact that you heard a loud metal bang when things went south indicates to me that something mechanical has failed either in the drive line (your inspection found no faults), or inside the final drive (rear end). If it's inside the final drive, shavings from the damage may plug the filter and cause the symptom noted above.
Note that damage can happen to some final drives that can still allow the tractor to operate normally for several hours before the filter plugs with debris. It's only when the grinding of the case gets loud enough to notice that it is realized that a failure has happened. On my GT, that was after a whole winter's snow removal, about 60-80 hours. Preliminary indications of how bad the failure was, was the shiny silver specs in the fluid as it drained out of the case. In my case, I didn't hear a bang when the bolts holding the differential carrier together broke, but a review of the tasks done over the previous months pinpointed when it occurred. My fault. The Sundstrand hydro is considerably stronger than the final drive and the GT was overloaded with ballast.
Go thru all of the linkages again, both hydro and brakes, and check for wear or damage. On the opposite side of the hydro from the drive control is a stub shaft that is almost flush with the housing. It is the other half of the trunnion shaft holding the swash plate and must move exactly like the control side. No slop allowed. If it moves correctly, the 1/4"x5/8" pins are in place and the problem is elsewhere.
If I recall correctly, there is also a shock absorber involved that can cause problems with the linkage and/or drive function.
The only problem with overfilling the hydro is that the fluid will spill out the vent when it warms up and will need to be cleaned up. If it is low, the drive will be jerky, or non-functional if the tractor is nose high as in climbing a slope. If it too low, none of the hydraulics will work.
