Do HSTs roll when on slight incline and no pedal / brake

[Volfandt]

Good answers. I'll just add my $0.02 too. A good rule of thumb w/any tractor, don't park it on a slope
A runaway tractor isnot a good thing
If you can't avoid it, drop the FEL and/or implement to help hold it in place.

HST's by their very design will creep. There is a sweet spot in an HST where the swash plate can rest in a position where it isn't putting enough fwd or rev pressure on the hydraulic motor to move the tractor and this is where every manuf trys to set it's neutral postion, thing is linkages wear as does the bearings, raceways etc., and it only takes a fraction of an inch for the neutral position be, well, not neutral. Theres adj's to every HST motion pedal/lever to get back to the neutral position but I wouldn't depend up the tractor sitting perfectly still just by placing the motion pedal/lever in neutral. To be safe, always set the brake if you want the machine to remain still and drop the implement(s) if you want it to stay put with the engine running for a longe period of time.

Good luck
Dave

 

[techman]

HST's by their very design will creep. There is a sweet spot in an HST where the swash plate can rest in a position where it isn't putting enough fwd or rev pressure on the hydraulic motor to move the tractor and this is where every manuf trys to set it's neutral postion, thing is linkages wear as does the bearings, raceways etc., and it only takes a fraction of an inch for the neutral position be, well, not neutral.
Dave

This is actually not the main problem. A HST has a hydraulic pump and motor, both of which have internal leakage. Simply put, the oil in the transmission "loop" is constantly leaking out and returning to the reservoir. This is true on every hydraulic pump and motor made, of this type. There is a charge circuit that keeps the loop filled at a relativel low pressure, but this internal leakage will always allow motor creepage when in the neutral position and a load is applied. This is why it will creep faster on a bigger incline, or in a higher gear. As the HST wears, the leakage will increase.

Leakage oil is the primary factor in the heat produced in the HST, if you are not stalled or otherwise hitting the relief valves.

A bit of reading:

Making Sense of Case Drain Leakage From Hydrostatic Transmissions

paul

 

[ZDB]

My M7040HD creeps.

that said with a wet disk brake system is there potential for the brakes to loose grip if parked for an extended period of time? Mine is always chocked with brakes off when storing so I've never checked.

 

[ruralruss]

My B3200 creeps. I usually leave it in M gear. It creeps faster if it is idling versus higher rpm. It also creeps much fast if I use the brake and release it.

 

[dfkrug]

A HST has a hydraulic pump and motor, both of which have internal leakage. Simply put, the oil in the transmission "loop" is constantly leaking out and returning to the reservoir. This is true on every hydraulic pump and motor made, of this type. There is a charge circuit that keeps the loop filled at a relativel low pressure, but this internal leakage will always allow motor creepage when in the neutral position and a load is applied. This is why it will creep faster on a bigger incline, or in a higher gear. As the HST wears, the leakage will increase.

Yes, good explanation, Paul.

To add to what you've said, a perfectly adjusted HST will creep downhill
on a slope with neither go pedal pushed. It will creep faster if you turn
the engine off, as the charge pump is no longer making up part of the
internal leakage.

When adjusting any HST pedals for the mid-position, the manuals clearly
state that the tractors are set for no movement with no external loads
(like slopes).

(Lots of HST tractors and slopes here!)

 

[rarvesen]

Thanks everyone, this was very helpful. I verified with the original people I spoke with, and I think it was a misunderstanding in the word 'roll'... roll means the tractor will not roll away picking up speed, but it will still 'creep' when on an incline.

 

[Tom_H]

Thanks everyone, this was very helpful. I verified with the original people I spoke with, and I think it was a misunderstanding in the word 'roll'... roll means the tractor will not roll away picking up speed, but it will still 'creep' when on an incline.

I would agree with that. It surely will move when on an incline. Speaking of the work roll, most of us use that particular word to mean rollover, definitely something you don't want to let the tractor do.

 

[kevinj]

Thanks everyone, this was very helpful. I verified with the original people I spoke with, and I think it was a misunderstanding in the word 'roll'... roll means the tractor will not roll away picking up speed, but it will still 'creep' when on an incline.

And if the engine quits it may run away as there will be no hydraulic pressure.

 

[Mighty Dodge]

With the engine stopped mine will slowly creep if on an incline and I forget to put on the brake.

 

[Don87]

I'm glad you all got that cleared up. I was getting ready to trade my Massey for the Bota............cause mine will go backwards or forwards(depending on the way I'm facing), whether the engine is running or not...........so I always use the parking brake.