hydrostatic transmission

[csr0831]

ok guys...I'm about to ask ANOTHER stupid question. I have a tractor with a hydro (GR2100). I am concerned about over taxing the tranny. Lets take a hypothetical situation. I would not do this, but for illustration purposes....if I were to take a chain and secure my tractor to a tree, take up the slack slowly and then when it was tight, push the pedal to the floor, what is happening internally? Assuming no wheel slippage, are there clutches inside that are slipping, is it a pure fluid drive??? IF anyone knows, I would appreciate them enlightening me : ) Thanks!

Chris

 

[aczlan]

ok guys...I'm about to ask ANOTHER stupid question.

the only stupid questions are those that dont get asked.

if I were to take a chain and secure my tractor to a tree, take up the slack slowly and then when it was tight, push the pedal to the floor, what is happening internally? Assuming no wheel slippage, are there clutches inside that are slipping, is it a pure fluid drive??? IF anyone knows, I would appreciate them enlightening me : )

inside the transmission is a hydro pump, that is connected to a hyd motor, inline with this is a "pressure relief valve", if you were to do as you say, that valve will go into bypass mode and prevent too much pressure (probbaly more than ~2500psi) from building up.


does that make any sense???

for more info try here: Hydrostatic transmissions or here: Hydrostatic Transmission,Hydrostatic Transmissions

Aaron Z

 

[Fordlords]

I have seen puller guys remove the bypass valves on old Sunstrands and just plug the holes to see what they can actually do in the "more power" fashion. In that event when over stressed, they most often start blowing out oil seals until the thing no longer can move the tractor. In normal working mode on garden tractor hydros with the pump-line-motor setup they just don't over stress even under very heavy use, and under regular use will last for decades. The same does not hold true for the fully integral hydros found on light lawn tractors- they will not withstand much abuse and are often just about toasted at the end of their typically projected 500 hour lifespans.

-Fordlords-

 

[Bird]

Aaron answered correctly, but I'll add one comment. Having the relief valve open in that situation won't hurt anything for a few seconds occasionally, but if you just sat there with it forcing the relief valve open, the hydraulic oil will get hotter than normal; i.e., don't do things that cause the valve to stay open for extended periods of time.

 

[csr0831]

Thanks guys. As I understand it then, no clutches in the conventional sense. The reason I asked is that I've got a Jonny Bucket on the thing and when shoving it into a pile of hard packed dirt, the machine will come to a stop and sometimes the front wheels spin, and sometiems they dont. The tranny will whine loudly and I let up on it and take another approach. Based on what I have heard this type of activity on and occational basis will not do signifiant damage to the machine, correct? Thanks again : )

Chris

 

[Bird]

Yep, nothing to worry about. That loud whine is when the relief valve opens, and as you said, it's time to take another approach.

 

[dfkrug]

If your HST goes into relief, and you hear the telltale squeal, your HST
pump is pushing oil at max pressure thru a small RV orifice. This heats the
oil up very fast, and when it exceeds a certain temp, you will get localized
boiling, which then scores your pump's swash plate. I don't know the GR1200,
but my Kioti, which has a 2500psi relief for the implement pump, has a 4000
psi relief for the HST. If you were to disable the HST RV, you will probably
stall the engine first, even at low swash plate angles.

 

[TimS]

Some hydro tractors (like mine) have an implement relief valve made specifically for use with a loader. My manual indicates that if I use a loader with the regular, non-loader relief valve, it may damage the transmission (and voids the warranty). Might be worth checking if you're in the same situation - awfully expensive to replace a transmission.

Tim

 

[dfkrug]

Some hydro tractors (like mine) have an implement relief valve made specifically for use with a loader. My manual indicates that if I use a loader with the regular, non-loader relief valve, it may damage the transmission (and voids the warranty). Might be worth checking if you're in the same situation - awfully expensive to replace a transmission.

Is this a small garden tractor? I wonder what a "regular non-loader relief
valve" is?

A compact tractor will have an implement pump to power the PS, as well
as any implements and/or the 3-point. Downstream from the implement
pump will be a RV on the tractor somewhere, then usually a RV comes with
each spool valve, whether the FEL valves, or any remotes. On these CUTs,
the HST hydraulics are entirely separate, except for the reservoir.

 

[TimS]

Is this a small garden tractor?

Relatively large garden tractor - JD455

I wonder what a "regular non-loader relief valve" is?

The one that came with the machine.



Don't know what type of tractor the original poster was referring to; just trying to make sure he didn't bust something. I know someone who bought an aftermarket loader for his 455, didn't think to swap the relief valve, and needed a new transmission the following week.

Tim

 

[csr0831]

Tim,
Thank you for being concerned enough to question it. The after market loader I have is not hooked into the hydraulics of the tractor. It lifts and dumps using electric actuators....designed for very light stuff (<200 lbs). The tractor is a GR 2100 (Kubota). Thanks.

Chris

 

[Rockfist]

Hi Chris -

So you bought the Johnny Bucket. I've been thinking about one for my GR2100. What are your impressions of it so far?

 

[csr0831]

Yep I got the bucket. Seems to be well made and designed. They did send the wrong front plate...the hole for the exhaust was cut in the wrong place. Turns out that they had not seen this model tractor with teh exhaust routed the way it was. I have one of the ealier model machines, so maybe Kubota made a production line change somewhere along the line...wouln't be unheard of. Anyway, they sent me a new plate and this one had the hole on the right side but the plate was too wide. Talked to 'em again and they sent ANOTHER plate, this time the hole was on the right side and the plate fit, but the hole was too high. Forth time they got it right. I really like it. As many have said, it is NOT a front end loader, but it serves my purposes well. I am more worried about the transmission in the GR holding up then I am about the Bucket. I have an older four wheel Gravely...I may get one for that too. I KNOW the transmission in that will hold up. : )

 

[Rockfist]

Funny thing about the front plate. You know, I think the GR2000 exhaust is routed differently than that of the 2100. I'll bet that yours is the first JB to be fit to a 2100. Thanks for blazing the trail for the rest of us!

I too, am concerned about the transmission. I just finished the 50 hr service, and chose to drain the transmission (instead of just change the filter, as the manual suggests). I was relieved to find no significant metal shavings in the screen. I've read about guys finding pretty large chunks of metal there, especially in the early production units.

I understand that this machine has a unique transmission, which may not be as robust as some when it comes to heavy pushing or pulling. However, it is a tractor, ******, and most components are fairly heavy duty (frame, engine). I pulled up a couple shrubs with mine the other day and all went well. I did have to tug on one of them a couple times to get it loose, though. I expect the machine to do at least moderate real work, above and beyond hauling me around as it mows the grass.

By the way: my neighbor has a slope on his property that's just about 30 degrees (I measured it). It's not long, only about 20 feet or so, but the GR2100 climbs it with ease. I can even stop part way up and get started again with no problem. Going down is no problem either - I think the transmission brakes all 4 wheels. There is no skidding or sliding.