DaveD
New member
Equipment
B1700 HST 1996, LP grading scraper & box scraper, Bush Hog SQ60 & aerator
I backed my 1996 B1700 HST with 1300 hours out of the shed on a very cold morning recently, temp about 20 F, and noticed shortly thereafter a puddle of hydraulic fluid on the floor below the dash cowling. It turned out that it was a leak out of the top seal of the power steering unit. Kubota shipped at least two versions of this unit with the B17/21/2400 tractors, and mine is an (the?) older version that has a simple cap with seal and retainer ring for the shaft going up to the steering wheel (see attached parts illustration). Cap is part 120, seal 430. I immediately ordered a replacement seal and the O-ring that serves as the gasket between this top cap and the body.
I've had the parts for a few days, but it hasn't leaked since. This seal replacement will probably be a relatively simple task, unlike on the newer versions, but I'm not sure now that I want to change it (the old adage "If it ain't broke, don't fix it" may apply here).
The input to the PS unit is directly from the flow priority valve at full pump pressure. One output goes to the 3PH control valve and the second to the PS unit. When exiting from the PS unit it is still under some pressure, but labeled "Low Pressure Oil" in the WSM illustrations (see second attached image). From the PS unit, the oil is routed through the oil cooler in front of the radiator, the HST oil filter, then to the HST unit, and along the way through three rubber hoses with hose clamps, where it powers the HST with sufficient "charge" pressure to supply the HST pump, with another pump, the HST charge pump, at the end of the circuit increasing the pressure in this line to a high enough level (when and if necessary?) to supply the HST pump and help the tractor move smoothly. The HST motor powers the tractor from the HSP pump. There is a charge relief valve in the circuit (top in second attachment) that suggests that the charge may sometimes be high enough to require a relief valve.
The reason for this thread is that I'm wondering whether this one-time oil leak may have simply been because of cold oil or a temperature-related restriction in this low pressure line that caused a pressure increase in the output PS unit side and made the seal leak. (The seal should be subjected only to output pressure.) The tractor has a new Kubota HST oil filter and a full load of new UDT-2 hydraulic oil, both changed by me a year or two ago with scheduled maintenance.
Anyone have experience with this sort of problem? I will wait until I hear from some of the experience here before attacking the job.
I've had the parts for a few days, but it hasn't leaked since. This seal replacement will probably be a relatively simple task, unlike on the newer versions, but I'm not sure now that I want to change it (the old adage "If it ain't broke, don't fix it" may apply here).
The input to the PS unit is directly from the flow priority valve at full pump pressure. One output goes to the 3PH control valve and the second to the PS unit. When exiting from the PS unit it is still under some pressure, but labeled "Low Pressure Oil" in the WSM illustrations (see second attached image). From the PS unit, the oil is routed through the oil cooler in front of the radiator, the HST oil filter, then to the HST unit, and along the way through three rubber hoses with hose clamps, where it powers the HST with sufficient "charge" pressure to supply the HST pump, with another pump, the HST charge pump, at the end of the circuit increasing the pressure in this line to a high enough level (when and if necessary?) to supply the HST pump and help the tractor move smoothly. The HST motor powers the tractor from the HSP pump. There is a charge relief valve in the circuit (top in second attachment) that suggests that the charge may sometimes be high enough to require a relief valve.
The reason for this thread is that I'm wondering whether this one-time oil leak may have simply been because of cold oil or a temperature-related restriction in this low pressure line that caused a pressure increase in the output PS unit side and made the seal leak. (The seal should be subjected only to output pressure.) The tractor has a new Kubota HST oil filter and a full load of new UDT-2 hydraulic oil, both changed by me a year or two ago with scheduled maintenance.
Anyone have experience with this sort of problem? I will wait until I hear from some of the experience here before attacking the job.
