ZD28 hydraulic drive problem

P

Pmschmitt

New member

Equipment
Rtv CPX1140, ZD28
Mar 17, 2019
22
0
0
Navasota, Texas
Just picked up a 2003 ZD28 with 630hrs. I picked it up cheap because the right side will not move. Engine runs well and the left side works. I have read a lot on this site about the problems with the ZD hydraulics, but I have not heard all the solutions. I am planning to do the work myself.

So where should I start, I have read they can need a new charge pump, hydraulic pump, and one or two drive motors which can all addd up to expensive. The following was my thought to start

Remove the hydraulic filter and screen, cut open the filter and see if shavings.

How do I determine if it is the charge pump, hydraulic pump or hydraulic wheel motor. Is there a step by step diagnostic process?

Thanks in advance
Paul
 
L

lugbolt

Well-known member

Equipment
ZG127S-54
Oct 15, 2015
4,835
1,588
113
Mid, South, USA
Pmschmitt said:
How do I determine if it is the charge pump, hydraulic pump or hydraulic wheel motor. Is there a step by step diagnostic process?

Thanks in advance
Paul
Click to expand...
With a pressure gauge and/or removal for visual inspection.

Remove filter and cut it open for inspection. If you have aluminum shavings in the filter, the charge pump is shot. If there's a lot of brass in it, one or both HST's failed. Remove and disassemble them for inspection. If you find that the charge pump is shot, you'll likely also find that the PTO clutch is damaged due to slippage and overheating, thus a total overhaul of the transmission would be, IMO, the best route to go.

The problem was lack of hydraulic fluid combined with lack of maintenance. In other words, they don't hold a lot of fluid and people do not change it often enough. The service manual has a specified hours for fluid/filter changes and in northern climates that's fine, but for us here in the South where the heat gets triple digit+ for 3 months during mowing season, the fluid needs to be changed more often-AND it MUST be super UDT2 ONLY (and nothing else). Kubota adopted a kit with another reservoir but it's just a crutch. More frequent fluid changes are the guaranteed answer, in other words prevention via maintenance. The "issue" was solved with the ZD300 series, which has two filters, a much larger charge pump, and more fluid capacity. No they do not retrofit to the ZD200's.
 
P

Pmschmitt

New member

Equipment
Rtv CPX1140, ZD28
Mar 17, 2019
22
0
0
Navasota, Texas
Filter removed and cut open. Only see aluminium specks no chunks no brass. I am going to tear into the charge pump tomorrow night I’ll let you know what I find. Can you elaborate on your PTO comments and the need for possibly a full transmission overhaul. Would you do that by tearing the whole thing apart and cleaning replacing? Just curious.
 
L

lugbolt

Well-known member

Equipment
ZG127S-54
Oct 15, 2015
4,835
1,588
113
Mid, South, USA
The pto clutch is powered by the charge pump. If charge pump fails while mowing heavy grass or weeds, it'll slip, and slippage will wear the clutch plates out prematurely. If that happens, the only way to access the pto clutch is to disassemble the center case.

On the bottom of the ZD2x transmissions there is a suction screen. It is attached to the bolt that holds the pick-up tube to the side of the center case. I would advise to remove the suction screen and see what if anything is on it. If you see "mud" (dark colored material), that is generally going to be your pto clutch friction plates. Typically if they're worn that bad, the oil will also stink to high heaven.

Being that you are not seeing any brass, the HST's may very well be ok.
 
P

Pmschmitt

New member

Equipment
Rtv CPX1140, ZD28
Mar 17, 2019
22
0
0
Navasota, Texas
Is there a difference in the zd28-ec and the zd28f? I downloaded a free WSM for the evening, but I have an F. Just curious in the differences. Thanks
 
P

Pmschmitt

New member

Equipment
Rtv CPX1140, ZD28
Mar 17, 2019
22
0
0
Navasota, Texas
Since the left side works and the right side does not, wouldn’t that mean the charge pump is working? I thought If charge pump was bad both sides did not work. Also the hydraulic deck is not working with runs off the right side so. I am leaving twords HST? But no brass in filter. I will post back when I get it out and torn down.

Should I do a pressure test before tear down?
Anyone know where I can get or rent the tools for this?
 
S

Sea Dog

New member
Mar 9, 2019
3
3
3
Washington, IN
You should definitely test your fluid pressures before tearing it down. Kubota wants a small fortune for their test kit but I made mine for just a few dollars. Assuming you have determined where to hook up the charge pump pressure test from the WSM, remove that large Banjo bolt ( item #60 on the Hydraulic Delivery Pipe parts page). It can be drilled and tapped for 1/8" NPT pipe thread. Then all you will need is to adapt it to a hose and find a 1000 pound gauge. When finished with testing, install a 1/8" NPT plug. Checking the High Pressure pumps requires only hooking up a hose; the threads are standard tapered 1/4" pipe threads. It is pretty congested around those ports so I hoisted mine up and hooked up to the ports on the bottom. You will need a 5000 pound gauge for this.

Removing the Transaxle takes several hours to do but it's not terrible hard. You will need a cherry picker or hoist to remove it from the frame. Very awkward,

I thought my HST was toast on one side but pressure testing revealed that the HP Relief and Check valve was worn out and the spring was weak. I can just about assure you that if you take it to a dealer they will just install all new kit ($2K) and give you a $4K plus bill.
 
P

Pmschmitt

New member

Equipment
Rtv CPX1140, ZD28
Mar 17, 2019
22
0
0
Navasota, Texas
Ok attached are the filter after being cut open and the screen I pulled out. Both the filter and screen appear to have excessive aluminum shavings. I did not see any brass or gooey brown pto parts in the screen. Soooo.... I have drilled out the “big” nut to check charge pump pressures. So that is where I am at. I am going to check hydraulic pressures tomorrow and will report back.

Can I use a general hydraulic fluid for my pressure checks etc. I hate to spend a bunch on super UDt right now just to pressure test as I will need to drain it again for repair. Thoughts?
 

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P

Pmschmitt

New member

Equipment
Rtv CPX1140, ZD28
Mar 17, 2019
22
0
0
Navasota, Texas
Ok I got the right hydro drive off and opened up. It appears the swash plate and bearing were damaged resulting in the inability of the hydro to function. There were ALOT of aluminum shavings present.

Here are some pics. Here is my question.
1) is it rebuildable?
2) a new unit costs $1900
3)why all looks like it needs to be replaced.
 

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J

Jim L.

Active member
Jun 18, 2014
815
87
28
Texas
Small reminder in midst of teardown excitement. The pistons in the pump are not the same as the pistons in the motor.
 
J

Jim L.

Active member
Jun 18, 2014
815
87
28
Texas
No, not joking. Check your WSM and it says not to mix the pistons as the pump and motor have different sizes.

You're doing good on this project.
 
L

lugbolt

Well-known member

Equipment
ZG127S-54
Oct 15, 2015
4,835
1,588
113
Mid, South, USA
Usually when they're that bad, it's best to replace the failed HST. Also open the rest of it up and get the aluminum out. Yeah it's got filters but all it takes is ONE tiny piece of trash to get into that $1900 HST to tear it to pieces again. One tiny piece.

In the pics, the motor assembly is junk. The port block is junk. Thrust bearing junk. Shaft junk. Entire side HST is therefore, junk.

Again, remove the opposite side too, inspect/flush/repair/replace as needed. Then open the center case up and get the stuff out of there too. That is, assuming you're up to an expensive long project.

That failure is not uncommon..."Usually" it's due to lack of "proper" maintenance. The WSM says to change fluid and filters every what 200 hours? On the 25/28 it needs to be more often than that, like every 100 hours and super udt only--especially if it's used in the heat that we see here in the Southern USA. There was a bulletin out that describes what fails and how and there was also a kit to address it-but that bulletin has long since expired since the ZD300 series mowers had a completely redesigned HST which was 1000x better in every aspect. They knew the 25/28 was inadequate after it was out for a few years.

I've often passed those mowers up because of HST issues. Had a ZD25 pop up last week with a weak RH HST, coulda got it for $600 running. But it's only worth maybe $2200-$2500 in good condition, and a new HST is, as you said, $1900 so it would've been a loss-and I ain't doing that.
 
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