Hydrostat question

[Roger66]

I'm a new tractor owner and I have a 2017 Mahindra 1526. I've never had a real tractor before, just lawn tractors. I've seen many great videos explaining how hydrostat works. but my John Deer lawn tractor must have an extra feature that my Mahindra does not have. On my little Deere no matter how heavy the load or how steep the hill, full pedal always equals full power. There must be a governor of some type on the swash plate reducing the swash plate angle as the load increases. On my Mahindra I need to do this myself backing off the pedal to prevent it from stalling. I was wondering if the feature I have on the little Deere had a name? I was wondering if I had bought a bigger Deere if it would have had this feature. Backing off the pedal is no big deal, but it was a bit of a learning curve on this tractor.

Thanks

 

[Wagtail]

Your systems depend on the engine revolutions to power the hydraulic pump(s). The higher the revs, the 'faster/slower' you can get the pedal to give you that speed... to a maximum of its full depression.

Your selected range [High/Low] will also determine this, depending on what you're using the tractor for.

I know that on my 4105, there's a sweet spot that I usually go to [a titch above 2000 revs] for any work I'm doing with it. Low selected for dragging or non-PTO work. High for everything else... unless I'm using the FEL for a more precision purpose. You'll figure it out with practice.

Of course, for PTO work, I bring the revs up to operate the implement... and bring the revs up to 2500/2WD/High for travelling on bitumen.

 

[kthompson]

On your lawn tractor, could you by chance run it for the blades and not the pulling capacity? My guess is the lawn tractor is not gear near as high as your Mahindra is.

 

[Roger66]

Forget PTO, I'm just talking about purely towing load. There is definitely some type of governor on this lawn tractor. I pull a super heavy firewood trailer up a steep driveway. When I run on level ground full pedal it zips along pretty quick, but climbing the hill of course it slows way down, I'm still at full hydro pedal. You hear the engine loading down, but it stays at full revs give or take. If I do the same with the Mahindra the engine revs start dropping and will stall if you don't back off the pedal. The Deere has just one speed range and the Mahindra has 3 ranges and behaves the same in all three ranges just more dramatic in high range of course. Even in Low the Mahindra can't pull that same heavy trailer up that same hill at full pedal without stalling or nearly stalling. The little 19 HP gas Deere can. This is not to say the Deere is better at all, it's just easier to drive. The Deere automatically slows down downshifting if you will as the load increases. On the Mahindra I simply need to reduce pedal slow down a bit and then it can easily out tow the little Deere. You just need to drive it different as People on this forum pointed out to me. Not really a problem at all, but that feature on the little Deere is nice and I was wondering if this could have been one of the advantages of buying a Green or Orange tractor? Me and the Mahindra are getting along fine now that I've learned how to drive it.

 

[nybirdman]

I have owned two Kubota HST tractors and they both worked the same;I am sure all similar "real"tractors are the same.Less pedal is more power and less speed in any range.I have a 26 HP JD mower and don't see the operation as you do;I do not try and tow anything with it though.
On the Grand L Kubota's;they offer "auto-throttle advance" that gears down/throttle up per the load.

 

[oldnslo]

The HST On your JD lawn tractor is only designed to absorb a very small portion of the total engine. Depending on transmission model possibly as low as 5 HP upto 12 -15 HP. The tractor slowing indicates either the drive belt is slipping or the the HST is leaking internally which will over heat the HST. The HST on your 1526 is designed (sized) to utilize all of your engine horse power. Some HST type vehicles do have " Horse power" or "automatic transmission" type control but this is rarely available on smaller HST's and I have never seen this on a lawn mower.

 

[k0ua]

In my JD Lawn tractor I have a hill that will stall the hydrostat but the engine is still screaming away at near full throttle speed. That little hydro wont in any way bog the engine down. If the hydro does stall, and by stall, I mean the wheels stop turning, if you back off of the hydro pedal, the wheels will begin to turn again. Just like any other hydro, less pedal means less speed and more torque. The hydros on our big tractors like my Kioti have the ability to bog down the engine if you range gear is high enough, but not that little JD, it is just so wimpy it stops turning. The engines in these mowers are way more powerful than the hydros. Of course the load on the engines is primarily the blades not the drive.

 

[ruffdog]

The JD may have a lighter bypass valve or internal leaks.

 

[Roger66]

I've had this Deere for probably 20 years. I think it originally had a Kohler 15HP engine, but a few years ago the connecting rod decided to break free of the oppressive engine block, then I loaded a cheap 19HP Briggs engine on it. There is definitely nothing wrong with the transmission it has been behaving this way since I bought it new and it has tremendous pulling power, but sadly an open rear and tiny tires limits traction. No slipping belts. You mention internal leaks, again I'm sure this is working as designed, but perhaps the JD has a pressure regulator bleeding off at X PSI effectively reducing the ratio. Whatever it is it's NICE! This little tractor has impressive pulling force as long as it has good traction like my paved driveway. The big tractor earns its keep in the lower traction areas.

Another feature this little Deere has that I miss is if the parking brake is set and you press the go pedal, nothing happens. On the big tractor it goes or tries to fighting the brake and makes a horrible noise if it the brakes slip. This can't be good for it. I know, I know operator error, but humans make mistakes.

 

[oldnslo]

Roger,
I looked at the parts break down for the LX255 HST and it may have relief valves for limiting the system pressure. Just shows valve but does not explain what they are. Dumping over these relief valves generates heat. I suspect that if you drive it this way for a period of time and then feel the transaxle it will be hot. Since this HST is sized way below the 19 HP it will reduce the travel speed Vs spinning the wheels or potentially blowing something up from over pressure.