Getting the bx ready for spring lately. I changed both fuel filters, changed hst fluid and filter, and put on a brand new set of wheels and ag tires. Previously it had turf tires. I checked hst dipstick after about 5 minutes of idling and all seemed ok. A couple days later I went out to put the tractor to work. I noticed that I could not make it up a hill in my back yard while in high range. It has been wet and the ground was really soggy. However, the issue wasn't necessarily traction related as I was not spinning the tires. I had the go pedal to the max and it just wouldn't go up the incline. I switched to low range and went right up. Did leave some depressions in the ground due to the soft soil. I've never had to switch to low range before to make it up that hill. The transmission has always whined some on that incline, but has climbed it anyway. I was back out there today after no more rain and 2 days of sunshine. Ground was a little wet, but significantly dryer than before. Tried again in high range with the same exact weight on the tractor. Went right up without issue. I did not have to switch to low range. The tractor now has about 3 more hours on it since the hst fluid and filter change. Is it possible there was air in the system that needed to be purged before allowing the hst system system to function at full capacity? Or some other reason for my findings?
Question after HST Fluid Change
- Thread starter Mad Duck
- Start date
- Views: 1463
texasjohn
Super Member
You were in high range, soggy conditions, uphill with pedal maxed to the floor.....but lower gear worked just fine.
Sounds normal to me.
The soggy conditions put a load on the vehicle somewhat greater than you normally experience under drier conditions. By definition, there exists a load where high range is not the right answer. Also, HST gets most power to the wheels when pedal is just SLIGHTLY depressed, NOT mashed all the way down. I assume you were at reasonably high RPM under all conditions mentioned. The whine you mention indicates that the HST is near the max it can do for the conditions. The soggy conditions tipped the load to beyond what the HST could handle.
The symptom you describe is natural and normal, having nothing to do with HST fluid change. It would have occurred under similar conditions prior to the change, IMHO.
Sounds normal to me.
The soggy conditions put a load on the vehicle somewhat greater than you normally experience under drier conditions. By definition, there exists a load where high range is not the right answer. Also, HST gets most power to the wheels when pedal is just SLIGHTLY depressed, NOT mashed all the way down. I assume you were at reasonably high RPM under all conditions mentioned. The whine you mention indicates that the HST is near the max it can do for the conditions. The soggy conditions tipped the load to beyond what the HST could handle.
The symptom you describe is natural and normal, having nothing to do with HST fluid change. It would have occurred under similar conditions prior to the change, IMHO.
dodge man
Super Star Member
The HST pedal is not like a gas pedal. Flooring it is like being in a higher gear. Just having the pedal down part way will allow it to climb the hill easier.
Yes, I had max revs and it was a no go. I guess it was just ground conditions. Was just wondering cause I did have other variables at play. Thanks.
My property is almost all hill. If I just push the pedal a little bit it doesn't climb. Have always had to push the pedal more on the hills than on the flat parts to get it to initiate movement from a stop. It is the same as with the HST lever on my garden tractor. Whether this is distance or resistance I'm feeling, I don't know, but I understand the overall principle.
oldnslo
Super Member
Mad Duck,
HST is in simple form a variable volume hydraulic pump driving a fixed dispalcement hydrualic motor. The heavier the load or the steeper the grade you are trying to climb the higher pressure is required. This higher pressure causes more internal leakage so you have to press a little harder on the go pedal to compensate for this leakage loss.
On HST transmissions full torque is achieved at maximum operating pressure. This may be achieved at 1/4 of pedal travel depending on how efficient the system is.
hope this helps you understand.
HST is in simple form a variable volume hydraulic pump driving a fixed dispalcement hydrualic motor. The heavier the load or the steeper the grade you are trying to climb the higher pressure is required. This higher pressure causes more internal leakage so you have to press a little harder on the go pedal to compensate for this leakage loss.
On HST transmissions full torque is achieved at maximum operating pressure. This may be achieved at 1/4 of pedal travel depending on how efficient the system is.
hope this helps you understand.
texasjohn
Super Member
oldnslo, thanks for the details...I had not heard the 1/4 pedal travel info before, good to know.,
