DK45 HST blues

K5lwq · Apr 9, 2023

So was it the power piston that was stuck? No. 53 on diagram.

Harry in Ky · Apr 9, 2023

K5lwq · Apr 9, 2023

Ok just making sure I was following you correctly. Not sure what the little ball does. Could it have been causing it to stick somehow?

Harry in Ky · Apr 9, 2023

I don't think so. I believe it's a plug for cross drilling through the piston. I don't think it sticks out far enough to touch anything. Not sure though, guess I could check that next time out there.

K5lwq · Apr 9, 2023

Maybe it is used as a check valve. That is about the only thing I could see on the diagram that might cause it to stick. Anything else I would think would be obvious. Issues like this can be tough to track down. Let us know how it goes.

Harry in Ky · Apr 9, 2023

Maybe so, I guess I could go back to the DH45 PDF that ptsg put up on my first thread. That book gives a thorough description of all the working parts in this thing, theory of operation and all that. When I read through all that I hadn't seen the inside of any of this yet.

A check valve in that area might be possible, but if so I would think if it were involved then the piston would probably free up once pressure and flow are removed. This thing hasn't run for a couple weeks now, and the piston was stuck until just today.

Harry in Ky · Apr 23, 2023

Time goes by and so little gets done. Here's an update for anyone who may be interested.

The parts availability for the hydrostat on this tractor is disappointing, to say the least. Kioti can't (or won't) supply much of anything for it any more. This tractor is barely ten years old. Kioti can supply some seals, but no O rings, gaskets, or much else. The five seals they did manage to produce cost nearly $200. That's disgraceful, and if I had thought to question it when I called to place the order, I would have passed on that too. I know the seals are available elsewhere, I just thought this was the practical way to go. Wrong again.

The seals finally came in, and were picked up on Friday last. I spent a few hours today installing them and reassembling the unit. With no gaskets, the choices are limited. I decided since the gaskets were mostly intact, and not ripped, torn, or seriously damaged, I would just put it back with a slight film of gasket sealant. Not enough to get any on the inside of the cases, but hopefully enough to keep seepage to a minimum. I know that has it's risks, but stripping everything off and using only sealant has risks as well. This was fastest, and all things considered, seemed like the best option to me.

The O rings are all going back, except the two on the piston. I was able to match them at a local hydraulic shop. The piston itself, once I removed the old seals, was found to have a small burr or something that I believe was causing it to stick. Without the O rings the piston would hang up in one spot which I was able to deal with by filing down some spots in one area. It was on the piston, not the case, and wasn't in a sealing area, so I doubt the "fix" will be a problem. Once that was done the piston would slide back and forth with one fingertip. It seemed free enough with new O rings installed as well, so I'm pretty confident it will work. Confident it won't leak? Maybe not so much.

Now to get it all back together and see what I've gained.

K5lwq · Apr 23, 2023

That is unfortunate that getting parts are that difficult! Kioti does seem to be more expensive for any parts for some reason.

I think I would have done the same thing with the gasket if it was intact. I don’t think you will have any leaks. I am betting it will be good as new when you get it back together.

dfkrug · Apr 23, 2023

Harry in Ky said:
The piston itself, once I removed the old seals, was found to have a small burr or something that I believe was causing it to stick.

Just saw this thread. Interesting.

I have worked on more than my share of tractor HSTs, but only one that was servo-controlled. A McCormick GX50. It also had an hydraulic accumulator, but that was to keep the PTO brake engaged, IIRC.

Anyway, I don't know how good your DK45 hydraulic schematic is, but you really need it to confirm how everything works, and where the pressure test ports are. There will be ports for forward and reverse as well as the servo circuit. And you can test them before splitting the tractor.

Sadly, of the CUT makers I am familiar with, HST internal parts have only been available from Kubota or Deere. Not so for Kioti or Bobcat, or McCormick. Ugh.

Harry in Ky · Apr 24, 2023

I'm not well versed in the servo control concept either. In fact, this is my first experience at it. Considering the lack of product support (parts wise) from Kioti on this particular issue, it may very well be my last.

That said, I think I understand enough about how everything works. Well enough to get me this far, and I suspect well enough to get me far away from it soon enough. I THINK the problem that started all this has been found, corrected, and hopefully behind us. As for pressure tests and test ports, I'm sure you're right in that regard, but as far as I'm concerned, the tractor was running well, the transmission was working just fine right up until this happened. Nothing was mentioned that led me to believe there were any pressure related problems experienced during tractor operation prior to this. When I got to it, checked the linkages, pedal travels, etc, I decided the problem was mechanical, not really pressure related. When I get it back in one piece and test it out again, I expect it to work. If it does, then I see no reason for pressure testing.

Member ptsg posted a link to a Kioti manual that I studied before actually tore into it, and it was very helpful. A world of difference between that and the so called manual Bobcat put out. If you're interested you're welcome to examine it for yourself. It does indeed explain most anything one would care to know. I will try and put the link below, but if it doesn't work out you can access it on my earlier thread.