If a hydro fails what part of it fails ???

[eee]

Guys,
We are getting some good dialogue now....
Do you think the failure problem is more of a contaminent problem than a heat problem ? If you keep good clean hydro oil, could the heat get you anyway ?
Or does the dirty oil cause the heat,which in turn causes the o-ring failure ?
Or is it the mode of operation what causes the most excessive heat ?

 

[Soundguy]

I'd have to guess that excessive heat will get you with clean or dirty fluid. However dirty fluid doesn't help in any case... I guess the heat would be the primary problem, and the dirty fluid an agrivating factor, or a secondary cause.

Soundguy

 

[RobS]

Hey, this is interesting /forums/images/graemlins/cool.gif What is the sealing between the pistons and the bores? If there is leakage does it just fall to sump? Are there valves or ports to control inlet/outlet during the pumping cycle?

More info, we need more info!!!

/forums/images/graemlins/smile.gif

 

[duane]

Rob,

In the hydro I had apart, nothing seals the pistons in the bores, just tight tolerances. Think of a spit ball in a straw. Too small of a diameter, alot of air leakage and it won't go to far. A nice tight fit, little air leakage and the baby really goes. In a hydro, there is some oil leakage, but the tight bore to piston tolerance only allows small leakage. It's these tolerances that open up under dirty oil or heat that allow more leakage and less pressure/output torque.

Only rubber products I'm aware of are the casing shaft seals.

Duane

 

[jinman]

Rob, the description by Duane is correct. The individual pistons do not have seals. There is a valve-plate on the back of the transmission which has o-rings and the external plumbing has o-ring seals, but the innards of the pump and motor do not have seals.

Also, think of the transmission like you would your hydraulic pump mounted on your engine. Where does the oil go if that pump leaks? ...on the ground, right? Well, the HST is a sealed package that is mounted inside a shell which is NOT a sump. If the HST leaks, the oil will leak out of the housing and onto the ground because the housing is not sealed. Think of the transmission housing as being similar to the cowling around a jet engine. It's just there for mounting the transmission and support. It doesn't seal and there is no fluid sump around the transmission.

The output of the transmission goes into a mechanical, geared transmission housing and that assembly is sealed and forms a continuous sump with the differential. There are two drain plugs for the hydraulic oil: one on the transmission and one on the differential. But, when you fill with hydraulic fluid, the differential fills up and then spills over into the geared transmission.

Okay, I apologize. You'll probably be sorry you asked me about this because I can be really long-winded. I'm attaching a picture of the transmission, but I didn't have time to label everything. I'll try to do that sometime this weekend and add more info if I haven't already bored you to death with details, details, details. /forums/images/graemlins/blush.gif

 

[RobS]

That's great Jim, thanks. I'm never bored learning more about how things work! Who knows, once I have a better understanding of what's in a hydro transmission I may run out and buy one /forums/images/graemlins/grin.gif

From your description and the picture it seems that any fluid blown by the piston/bore clearance will not end up on the floor but rather in the hydro case. Kind of like the crankcase to an engine maybe?

Keep those details coming. I hope you can post some pics of the inner workings /forums/images/graemlins/smile.gif

 

[kensfarm]

I'll second that.. "Thankyou.. Jinman".. I've always been the type to "want" to be able to fix/work on the equipment I use. And most stuff I can.. but a lot of "fixing" on cars & such these days requires special equipment. The other half of it.. is having the time to do it.

 

[texbaylea]

Followup re: Kubota Grand L. Looking at the manuals for my L3130HST the motor is a fixed displacement type, the pump is a variable displacement with the swash plate controled by hydraulic servo via the treadle. The motor output then goes through a three range mechanical (gear) transmission to the differential.

I would guess that pump/motor wear would be the ultimate cause of transmission failure apart from simple breakage. There is nothing electronic about this transmission except status indicators such as range, PTO rpm, travel speed.

Vernon

 

[jinman]

Vernon, that all sounds simple enough except for the hydraulic servo. It's interesting that NH has a swashplate (I called it wobble plate before) that's a straight mechanical connection to the pedals and Kubota uses the servo. Does the fixed hydraulic pump get fluid directly from the sump or does it have some type of additional charge pump? Suddenly NH's hydro sounds a lot more complex than Kubota's, and I'd bet the JD E-hydro is even more complex with it's load-sensing ability. /forums/images/graemlins/confused.gif

 

[slowrev]

Jinman,
If there are no seals, etc inside the Hydro portion of the tranny are the cylinders/pistons replaceable after they wear out or is it a get a new Hydro kind of thing ? Just curious

Ben