DK50SE stuck in low range
- Thread starter Oscarveg08
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grsthegreat
Super Star Member
Ive torn into manual transmissions in the past......to me there no fun. Some people love that stuff....not i
k0ua
Epic Contributor
Hydrostatic transmission are also gear transmissions too. Every hydro has either a 2 speed or a 3 speed standard old unsynchronized gear transmission after the hydraulic motor and before the final drive gearing. A hydro is the combination of hydraulic piston pump (variable displacement) controlled by a swash plate (your foot controls this either directly or hydraulically coupled) and a usually fixed displacement hydraulic motor (Kubota and some others may have a 2 speed motor in premium models) and that hydraulic motor drives that gear transmission, and then on to final reduction and if 4 wheel the transfer lever/gearing to the prop shaft up front.
Manufactures prefer to call this transmission the "range control", but it is nothing but a simple geared transmission.
Of course I left out the prime mover (the engine) and some have a dry clutch and some don't before the hydraulic variable displacement piston pump.
Good explanation:thumbsup: I just didn't think there was that many gears in a hydro, so guess its like a gear trans with a hydraulic pump for shifting, wonder if this is the same pump that goes to the FEL and 3-point lift............
k0ua
Epic Contributor
No it is NOT for shifting. The pump is driven by the engine, and then the fluid flow (and directional flow) is what makes the hydraulic motor spin either forward or backwards. No it is NOT the same pump that drives the hydraulic system for the FEL and 3pt. However most designs for CUTS has a smaller second section to the main hydraulic pump that drives the power steering and many also provide the function of "charge pump". This is a low pressure (about 250 psi) section of the pump that provides "make up" fluid that makes up for fluid losses inside the main piston pump. The pistons are riding on "slippers" (wear surfaces) that move around the swash plate. The swash plate is at zero degrees deflection when NEITHER pedal is pressed, so the pistons do not ride either up or down the swash plate, they just go round and round and no appreciable fluid flow from the 9 pistons (usually) goes back to drive the hydraulic motor. So the hydraulic motor just sits there and does not provide any torque to the gear train of the 3 speed gear transmission. So your tractor sits like a rock.
Don't think of a hydro like an automatic transmission, because it is NOTHING like an automatic transmission with its fluid logic, valves, and clutch packs. NOTHING.
When you move the swash plate, either by direct mechanical action (SCUTS and many CUTS) or with hydraulic assist (Larger CUTS) by moving one or the other pedals, either forward or backward (Kubota's usually have only one pedal, but it still moves either forward or backward) it moves the swash plate angle.
Now that the swash plate is angled, the slippers will have to climb "uphill" and as they do so the cylinder bores, filled with fluid, will push out that fluid when they come around to the discharge port(S), This pushed fluid toward the hydraulic motor which starts to spin in the proper direction depending on which way the fluid is flowing depending on which angle from centered the swash plate is, depending on which pedal was pushed by the operator.
Of course one diagram or you-tube video would be worth about 10,000 of my typewritten words.
k0ua
Epic Contributor
By the way, the pressures toward the Hydraulic motor may reach as high as 5000 PSI (for CUT sized tractors) before the hydrostat relief valve opens. This relief valve will open of course like any other relief valve when its pressure is exceeded, Like for instance when the tractor has good traction with the ground, and it is pushing up against an immovable object (tree, stone wall) AND its transmission gear is selected to HIGH.
So if you choose High range (stupid thing to do) and you try to push over a big tree, and you start pressing on the forward pedal the pressure will rise between the pumps discharge port and the hydraulic motor because the hydraulic motor is looking into a highly geared gear train that will not move, and the wheels will not spin because the gear selected is too high and not enough torque can be developed to spin the tires on the ground. Of course if a LOW or MED gear range was selected by the operator then the wheels would rotate, the tires would spin on the ground and the pressure relief valve in the hydro unit would not open because its ultimate pressure would not be achieved.
This action is no different than choosing too high of a gear in a simple standard transmission only tractor. Only here the limiting factor is how long will the clutch last, how powerful is the engines ability to burn up that clutch, and how stupid is the operator?
Higher gear=higher overall speed but lower torque that can be delivered.
Lower gear= lower overall speed but higher torque that can be delivered
Smart operator=longer clutch life.
Moron operator=short clutch life.
But with hydrostatic transmission, there is a built in safety mechanism of the hydro relief valve and just fluid coupling from pump to motor, so yes fluid can get hot if moron operator persists, but for short time periods, no damage is done, unlike damaging a clutch facing.
So if you choose High range (stupid thing to do) and you try to push over a big tree, and you start pressing on the forward pedal the pressure will rise between the pumps discharge port and the hydraulic motor because the hydraulic motor is looking into a highly geared gear train that will not move, and the wheels will not spin because the gear selected is too high and not enough torque can be developed to spin the tires on the ground. Of course if a LOW or MED gear range was selected by the operator then the wheels would rotate, the tires would spin on the ground and the pressure relief valve in the hydro unit would not open because its ultimate pressure would not be achieved.
This action is no different than choosing too high of a gear in a simple standard transmission only tractor. Only here the limiting factor is how long will the clutch last, how powerful is the engines ability to burn up that clutch, and how stupid is the operator?
Higher gear=higher overall speed but lower torque that can be delivered.
Lower gear= lower overall speed but higher torque that can be delivered
Smart operator=longer clutch life.
Moron operator=short clutch life.
But with hydrostatic transmission, there is a built in safety mechanism of the hydro relief valve and just fluid coupling from pump to motor, so yes fluid can get hot if moron operator persists, but for short time periods, no damage is done, unlike damaging a clutch facing.
"Don't think of a hydro like an automatic transmission, because it is NOTHING like an automatic transmission with its fluid logic, valves, and clutch packs. NOTHING."
I cant help it thats what I keep thinking, maybe when the OP gets his tractor all together I might get a better idea of why a hydro has so many gears.........
I cant help it thats what I keep thinking, maybe when the OP gets his tractor all together I might get a better idea of why a hydro has so many gears.........
ptsg
Super Member
Imagine a CVT transmission of a UTV or something similar. The HST is similar on how it varies the speed but it's done using fluid instead of a belt like the CVT and has the ability to reverse without extra gearing.
k0ua
Epic Contributor
Yes the ability to instantly reverse under power is one of its best features. Because there is no mechanical connection between the engine and the final drive, there is nothing to wear or break. It is just a matter of changing the fluid flow direction (out this port instead of that port) by the angle of the swash plate, controlled by the operators foot.
A hydro is a simplified gear tractor, except no reverse gear and a very limited set of gears, in CUT sizes no more than 3 gear sets.
The other redeeming featear is the abllity to have and infinate ground speed up to the maximum allowd by the chosen gear range. But they are all zero to the maximum allowed by the gearing and engine rpm. But torque will not be equal in the ranges. Torque will be greatest in low range, be medium in Med range and least in High range. Just like any standard geared transmission. Nothing changes here, except the ground speed is not regulated by the engine speed so much, as the engine in normally operated (exceptions to every rule) more like a stationary engine you are extracting power from at a set RPM (effeciency spot for the engine) and applying varying amounts of fluid flow by adjusting the swash plate with your foot.
OP
Oscarveg08
New member
- Joined
- Aug 15, 2020
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- Tractor
- 2013 Kioti DK50SEHC
That’s the one! It was JB welded and leaking a good amount of hydraulic fluid.Is this the crack......
