New GR2120 creeps on hills - normal?

[Spimly]

I just purchased a new GR2120 lawn tractor and have to say I really like it. However it has one 'feature' that I'm concerned about. Regardless of the way I'm facing on a hill (down or up), the tractor will creep down the hill when my foot has released the treadle pedal. It seems to creep faster when facing downhill compared to facing uphill. If I lift up on the pedal with my foot, it will stop creeping. This is a big concern to me because I have several areas that I mow where I back down to the edge of a brook and further unexpected travel in that direction could spell major trouble.

I talked to the service person at the dealership and they say that is normal and there is nothing they can do about it. They did say that tapping the treadle in the opposite direction should stop the motion - it doesn't. For instance, when mowing downhill, I can put the treadle in the neutral position, tap the rear direction side of the treadle until the tires are going in reverse, take my foot off the treadle, and it still creeps downhill.

On the flat, the neutral position works as expected.

So is this normal? I can't believe that Kubota would design the HST knowing this issue exists. It seems like a major flaw, assuming there is no adjustment to fix it. I asked this same service tech about the "HST Neutral Position" adjustment in the shop manual and they said it wouldn't fix this problem.

So what do you good people think?

Barry

 

[TheOldHokie]

I just purchased a new GR2120 lawn tractor and have to say I really like it. However it has one 'feature' that I'm concerned about. Regardless of the way I'm facing on a hill (down or up), the tractor will creep down the hill when my foot has released the treadle pedal. It seems to creep faster when facing downhill compared to facing uphill. If I lift up on the pedal with my foot, it will stop creeping. This is a big concern to me because I have several areas that I mow where I back down to the edge of a brook and further unexpected travel in that direction could spell major trouble.

I talked to the service person at the dealership and they say that is normal and there is nothing they can do about it. They did say that tapping the treadle in the opposite direction should stop the motion - it doesn't. For instance, when mowing downhill, I can put the treadle in the neutral position, tap the rear direction side of the treadle until the tires are going in reverse, take my foot off the treadle, and it still creeps downhill.

On the flat, the neutral position works as expected.

So is this normal? I can't believe that Kubota would design the HST knowing this issue exists. It seems like a major flaw, assuming there is no adjustment to fix it. I asked this same service tech about the "HST Neutral Position" adjustment in the shop manual and they said it wouldn't fix this problem.

So what do you good people think?

Barry

Thats the way my G2160 and G2460 behave. I strongly suggest you avoid backing up to or driving forward to the edge of dropoffs. Its a high risk manuever and sooner or later it will bite you.

Dan

 

[GreensvilleJay]

Curious, doesn't the parking brake work ?
Sounds like the HST doesn't have a true 'neutral' where the motor is physically disconnected from the drive train. Don't think I've ever seen one that does. I KNOW hydro-gear and tuff-tork HST don't disconnect.
You should be able to MINIMIZE the 'creep' though by adjusting the HST treadle linkages / spring tensions.

 

[NCL4701]

I don’t have a GR so maybe what they call a HST in a GR is different than a HST in a tractor?

The HST in a tractor (and unless it’s some sort of marketing crap, I assume it’s the same in a GR) is a variable displacement multi-piston hydraulic motor with a swash plate, the position of which controls direction and speed. The difference between a variable displacement piston motor and a variable displacement piston pump is when it’s acting as a motor it has hydraulic oil forced into it under pressure causing it to turn; the fluid power coming in goes out as rotational power. When it’s acting as a pump, it’s rotated by a motor and that rotational power coming in goes out as fluid power.

So when you move the swash plate with the pedal, it acts as a motor and moves the mower forward or backward. When it’s on a slope and you take your foot off the pedal or otherwise have it in the neutral position, the wheels are trying to turn the variable displacement piston motor/pump that is the machine’s HST, so it starts acting like a pump. Of course, there’s significant resistance to that rotation provided by the hydraulic oil in the circuit and on flat ground or a slight slope that fluid resistance may be sufficient to hold it in place. However, that braking effect is more of a collateral feature intrinsic to the design than an effort by the designers to create some sort of transmission/brake combination.

That long winded explanation leads to a pair of operating practicalities.

First, when you were told tapping the pedal in the direction opposite the roll would stop it: yeah, if you bump it a little in the opposite direction and hold it. As soon as you let the pedal return to neutral the undesired roll condition will immediately return.

Second, although I don’t have a GR, I assume it has brakes. As explained above, the HST sort of acts kind of like brakes in some scenarios, but it ain’t brakes. You still have to use brakes sometimes.

Edit: BTW, that’s not a Kubota thing. That’s a HST thing.

 

[mikester]

I just purchased a new GR2120 lawn tractor and have to say I really like it. However it has one 'feature' that I'm concerned about. Regardless of the way I'm facing on a hill (down or up), the tractor will creep down the hill when my foot has released the treadle pedal. It seems to creep faster when facing downhill compared to facing uphill. If I lift up on the pedal with my foot, it will stop creeping. This is a big concern to me because I have several areas that I mow where I back down to the edge of a brook and further unexpected travel in that direction could spell major trouble.

I talked to the service person at the dealership and they say that is normal and there is nothing they can do about it. They did say that tapping the treadle in the opposite direction should stop the motion - it doesn't. For instance, when mowing downhill, I can put the treadle in the neutral position, tap the rear direction side of the treadle until the tires are going in reverse, take my foot off the treadle, and it still creeps downhill.

On the flat, the neutral position works as expected.

So is this normal? I can't believe that Kubota would design the HST knowing this issue exists. It seems like a major flaw, assuming there is no adjustment to fix it. I asked this same service tech about the "HST Neutral Position" adjustment in the shop manual and they said it wouldn't fix this problem.

So what do you good people think?

Barry

There is a reason for the parking brake

 

[Spimly]

There is a reason for the parking brake
View attachment 131041

Funny. But this is not a parking issue, it's a driving issue.

 

[Spimly]

I don’t have a GR so maybe what they call a HST in a GR is different than a HST in a tractor?

The HST in a tractor (and unless it’s some sort of marketing crap, I assume it’s the same in a GR) is a variable displacement multi-piston hydraulic motor with a swash plate, the position of which controls direction and speed. The difference between a variable displacement piston motor and a variable displacement piston pump is when it’s acting as a motor it has hydraulic oil forced into it under pressure causing it to turn; the fluid power coming in goes out as rotational power. When it’s acting as a pump, it’s rotated by a motor and that rotational power coming in goes out as fluid power.

So when you move the swash plate with the pedal, it acts as a motor and moves the mower forward or backward. When it’s on a slope and you take your foot off the pedal or otherwise have it in the neutral position, the wheels are trying to turn the variable displacement piston motor/pump that is the machine’s HST, so it starts acting like a pump. Of course, there’s significant resistance to that rotation provided by the hydraulic oil in the circuit and on flat ground or a slight slope that fluid resistance may be sufficient to hold it in place. However, that braking effect is more of a collateral feature intrinsic to the design than an effort by the designers to create some sort of transmission/brake combination.

That long winded explanation leads to a pair of operating practicalities.

First, when you were told tapping the pedal in the direction opposite the roll would stop it: yeah, if you bump it a little in the opposite direction and hold it. As soon as you let the pedal return to neutral the undesired roll condition will immediately return.

Second, although I don’t have a GR, I assume it has brakes. As explained above, the HST sort of acts kind of like brakes in some scenarios, but it ain’t brakes. You still have to use brakes sometimes.

Edit: BTW, that’s not a Kubota thing. That’s a HST thing.

Thanks for taking the time to explain this. I've spent the last 36 years on two Simplicity lawn tractors and I did not have this issue. That's why it surprised me that something as costly as a Kubota would have it. I will say that the Simplicity's had dual controls for direction, not a single control.

What that explanation doesn't explain is why when I pull up from the underside of the treadle pedal, the motion stops. Am I in essence applying a small opposite direction input to the HST?

 

[GreensvilleJay]

yes.....
as for 'neutral', that's based upon the 'mechanical geometry' of the pedal to HST connection.

generally for riding mowers there's a LOT of freeplay (aka slop) in the fwd-new-rev mechanics, after all it's a cheap,mass produced mower compared to a 'farm tractor', that requires a more precise control of direction

Now my BX23S does have a good pedal neutral. It does NOT creep on level ground,but I do keep the pedal greased. Still I use the parking brake.If I don't and park on a slope, engine off gravity WILL move the machine. Nature of the beast.

 

[TheOldHokie]

Thanks for taking the time to explain this. I've spent the last 36 years on two Simplicity lawn tractors and I did not have this issue. That's why it surprised me that something as costly as a Kubota would have it. I will say that the Simplicity's had dual controls for direction, not a single control.

What that explanation doesn't explain is why when I pull up from the underside of the treadle pedal, the motion stops. Am I in essence applying a small opposite direction input to the HST?

Thanks for taking the time to explain this. I've spent the last 36 years on two Simplicity lawn tractors and I did not have this issue. That's why it surprised me that something as costly as a Kubota would have it. I will say that the Simplicity's had dual controls for direction, not a single control.

What that explanation doesn't explain is why when I pull up from the underside of the treadle pedal, the motion stops. Am I in essence applying a small opposite direction input to the HST?

My guess is unlike the new Kubota your Simplicity lawn tractors used a vertical shaft air cooled engine on top of an commodity integrated transaxle.

Open the hood on the Kubota and look at the 3 cylinder diesel tractor engine coupled to the HST which is then coupled to the rear axle. Thats a considerably different and heavier duty design.

Dan

 

[NCL4701]

Am I in essence applying a small opposite direction input to the HST?

As GreensvilleJay already said, yes.

 

[mikester]

Funny. But this is not a parking issue, it's a driving issue.

If you have two feet you can operate the brakes on steep slopes.

I think most experienced operators acknowledge that HST machines can still roll given enough slope.

The heavier the machine the harder it is to hold on slopes. Fact of life.

 

[Spimly]

If you have two feet you can operate the brakes on steep slopes.

I think most experienced operators acknowledge that HST machines can still roll given enough slope.

The heavier the machine the harder it is to hold on slopes. Fact of life.

Parking brake is on the same side as the treadle pedal on this tractor. Having two feet doesn't help.

 

[Grandad4]

So is this normal? I can't believe that Kubota would design the HST knowing this issue exists. It seems like a major flaw, assuming there is no adjustment to fix it.

Can't improve on the explanations here but maybe you could compare it to driving a car with an automatic transmission. Nobody thinks twice about keeping their foot on the brake at a stop because the car is made to roll freely (well, almost freely) when you take your foot off the accelerator. The car does not apply the brakes automatically and neither does your GR mower. The HST will bring you to a stop gradually but it's your job to keep it there.

 

[TheOldHokie]

Parking brake is on the same side as the treadle pedal on this tractor. Having two feet doesn't help.
1

I have been operating two of these machines on very hilly land for 15+ years and I fail to see the problem. On a slope it drifts in neutral and you control that using the HST OR brake pedal as needed. Why would you ever need to use them simultaneously?

Dan

 

[GreensvilleJay]

GREAT analogy about a car with autotranny !!!
Hmm, any other two footed autotranny drivers here ?

 

[Sidekick]

Can't improve on the explanations here but maybe you could compare it to driving a car with an automatic transmission. Nobody thinks twice about keeping their foot on the brake at a stop because the car is made to roll freely (well, almost freely) when you take your foot off the accelerator. The car does not apply the brakes automatically and neither does your GR mower. The HST will bring you to a stop gradually but it's your job to keep it there.

Our 2 vehicles have hill assist and once you stop on a hill you are stopped until hitting the gas pedal without using the brakes. I think most newer vehicles have it and could be why some haven't experienced needing 2 pedals before.
My bx does the same freewheeling with the pedal centered. With the parking brake on the same side as the rocker pedal and so high above it it's basically useless. Get used to using reverse to control it.

 

[TheOldHokie]

Get used to using reverse to control it.

I think that took me just slightly more than a nanosecond.

Dan

 

[GreensvilleJay]

re: hill assist and once you stop on a hill you are stopped until hitting the gas pedal without using the brakes.

wow, more garbage electronics and 'computer' and 'stuff' that real drivers do NOT need AND bet that 'feature' is very pricey to repair !

Instead of dumbing down the cars, they should EDUCATE the drivers.

 

[TheOldHokie]

re: hill assist and once you stop on a hill you are stopped until hitting the gas pedal without using the brakes.

wow, more garbage electronics and 'computer' and 'stuff' that real drivers do NOT need AND bet that 'feature' is very pricey to repair !

Instead of dumbing down the cars, they should EDUCATE the drivers.

The simple fact is consumers like it and if OEMs want to compete they need to offer it.

Dan

 

[Sidekick]

re: hill assist and once you stop on a hill you are stopped until hitting the gas pedal without using the brakes.

wow, more garbage electronics and 'computer' and 'stuff' that real drivers do NOT need AND bet that 'feature' is very pricey to repair !

Instead of dumbing down the cars, they should EDUCATE the drivers.

Actually the speed sensors are already in the wheels and computer controls the brakes so it's just a couple lines of code that doesn't cost much. Everything is pricey to buy and repair these days. Just had a new refrigerator stop getting cold after 5 months and the manufacturer is refunding my money because it would have cost more to fix or replace then it cost to buy.