DK45 HST blues

Harry in Ky · Apr 9, 2023

The tractor in question is branded as a Bobcat CT445 but it's still Kioti. Posting this here because I'm thinking the Kioti name may have more "eyes" on it.

It's a DK45 HSE tractor as far as I can see. The problem is this. The hydrostat decided one day to stick in the forward direction. The story as told to me, the tractor was running along as usual with no noticeable problems. Driver stops to open a gate, gets back on and can't get the range shifter to go into gear. Gears are grinding and it just won't shift. Also of note is the reverse pedal has no travel. It's pretty much solid in the neutral position.

A quick look at the external pedal links and pivots shows nothing unusual. After removing a few of the points and joints it turns out the pedals are both operating as the should, the problem is the control shaft going into the hydrostat will not move in the direction of reverse travel. Now what? I tried turning that shaft with a large Crescent wrench and decided that any more force in that direction was probably going to break something.

Searching for information on this tractor and it's transmission I find it's designed with a servo piston operated swash plate. I'm not sure how common that concept is, but my limited hydrostat experience has all been with strictly mechanical operation. I concluded that anything related to this piston mechanism is only accessed from the inside, so any work done on it means the unit come out of the tractor. I finally got the tractor in three pieces on Friday and got the unit out on the floor. Removed the two covers and exposed the piston, which was indeed stuck in the forward position. I now have the unit in another location where I have a reasonable shot at keeping everything clean while it's apart.

I did that today, and expected to find something broken, twisted, jammed, etc in either the piston/bore, or the swash plate mechanism on the inside. Following the procedure I got the pump rotating group out exposing the swash plate and found no problems at that point. Removing the plate requires the piston to be in the neutral position, so at that point I decided to give the piston a little "tap" in that direction, and it moved. Now with the swash plate out everything behind it looks normal, and the piton will go full travel in both directions with just enough effort to overcome the drag of the O rings. WTH? Took it all apart and put it together two or three times, and can't find anything wrong with what I see. I took the valve spool out of the piston, looked everything over hoping to find a piece of SOMETHING to justify the piston sticking in first place.

Now I'm really lost as to what to do next. I don't see anything I feel a need to replace other than seals, gaskets, and O rings. I see nothing at all to justify why I should be into the thing this deep.

I guess I'm grasping here, hoping someone has some experiences to share concerning anything similar on this style unit. At this point I'm not sure what else to do other than put it all back and hope it doesn't do that again?

K5lwq · Apr 9, 2023

At this point not sure what else you could do other than a complete new unit. I would be inclined to put it all back together and hope for the best! I hate not finding the cause of issues and things start working again. But often times when that happens it keeps working so who knows.

oldnslo · Apr 9, 2023

Where is the valving for sending pilot signal to the control piston and how is it controlled? If the pilot valve was stuck it would drive that piston over whenever the tractor was running but I would expect it to vent back to zero pressure when engine was off.

Harry in Ky · Apr 9, 2023

Pilot valve is inside the piton. It's not nor was it ever stuck. Before disassembling anything else the actuating control lever was removed exposing the valve. It could easily be moved back and forth against its spring pressure with little effort. It was the piston the valve operates that was stuck.

Harry in Ky · Apr 9, 2023

Bobcat Genuine Parts Catalog – Official Bobcat Company site

Not sure if this link will work or not, I've never tried to link to this site. This is a breakdown of the uniy I have apart.

Harry in Ky · Apr 9, 2023

That's what I expected. Only goes to home page. Not much help.

Harry in Ky · Apr 9, 2023

OEM Parts Nolt's Power Equipment LLC & Perry Power Equipment

OEM Parts Nolt's Power Equipment LLC Shippensburg, PA (717) 423-6300

www.noltspower.com

Let's see if this works.

Harry in Ky · Apr 9, 2023

It works on my end

K5lwq · Apr 9, 2023

Works for me.

Harry in Ky · Apr 9, 2023

I guess my next step tomorrow is to check the local Bobcat and closest Kioti parts counters and see what seals, gaskets, and O rings are available. The Bobcat parts list shows many of those I would like to replace are listed as NLA. Maybe Kioti will be more help.

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.