Hydro Drive Question

[rims421]

I have a question regarding the hydro drive on my cub 7275.
I was working the tractor skidding some trees i had cut down.
The tractor would be pulling pretty hard in reverse with a fairly large tree chained to the bucket. At some point with the tractor in mid range 4wd if i encountered additional resistance(like the rear wheels falling into a slight depression)
the wheels would no longer turn. If i put the machine in low range it would begin to turn the wheels again. The machine is operating in a heavy snow crust. Is this normal? I thought the machine should either stall out or the wheels should turn. It does not seam to be a problem going forward. I was going to check the adjustment on the foot pedal for starters. Any other suggestions / advice? /forums/images/graemlins/confused.gif

 

[Bird]

Sounds completely normal to me; just have to change to low range when that happens.

 

[OkeeDon]

I'm venturing into territory here that I'm not quite sure I know enough about, but if I say something wrong, the real experts will jump in and correct me -- I hope.

Here's how I understand it. There is no direct mechanical connection to the wheels like there is in a gear tractor, but a hydraulic motor. As I understand it, a hydraulic motor does the same thing as a hydraulic cylinder, except it makes things go round and round instead of in and out.

Now, think about what happens when you try to lift something that is too heavy for a hydraulic cylinder. It doesn't stall the engine or jump and clatter, it just quits. I assume there is some sort of internal bypass, but I don't really know. The same thing happens when you ask your hydrostatic tractor to move more than it is capable of moving -- the wheels don't spin, the engine doesn't stall -- it just quits. Shift to the lower range and you're doing something to the circuits that multiplies the power but cuts the speed, and it moves again.

Now, that's not to say that you can't stall it; I've had my tractor stall when I ask it to do too much -- in the lowest range. In the higher range, it just doesn't move.

That's not a very technical explanation, but it describes in amateur terms what happens, as I've observed it.

 

[Bird]

</font><font color="blue" class="small">( I assume there is some sort of internal bypass, but I don't really know. )</font>

I think that's a pretty good explanation, Don. And that bypass is the relief valve opening which doesn't really hurt anything if you don't just sit there and keep it open which would tend to make the hydraulic oil get hotter and hotter.

 

[MossRoad]

Real nice explanation, Don. /forums/images/graemlins/smile.gif

 

[jinman]

Oh Bird! I was hoping you would call it by it's real technical name, the relief "thingy." /forums/images/graemlins/blush.gif /forums/images/graemlins/laugh.gif

 

[JDgreen227]

Jinman,

You obviously did not study spelling during your last year or two of education....the correct technical term would actually be THINGAMABOB.

Don, that was a very well written explanation, much better that I could have provided.

 

[OkeeDon]

Thanks for all the kind words. Only, now I'm going to have to go to Wally World and get a new $6 straw hat in a bigger size. /forums/images/graemlins/crazy.gif

 

[rims421]

Thanks for the good news.
I did not want to even think about having to deal with a repair to the hydro tranny.

You guys are the CUT gods.

 

[RobertN]

Do you know how hard it is to 'splain that to someone from outside the US? I used to work at the company that probably made the CPU in your computer. I worked in a failure analysis lab, and had people from all over the world that worked in similar labs, come in for testing products.

I tried saying"Grab that dohicky over there", just to be a funny guy. It was really hard to explain why I called it a dohicky and how it could be a dohicky and thingamjig depending on who looked at it.

After in depth explanations, some were amused, some not /forums/images/graemlins/wink.gif