Vintage ZD28 HST Repair Help

Spicy Chicken

New member

Equipment
ZD28, ZD1211
Mar 7, 2023
7
4
3
Ontario
Hi all,
New member here and have very little knowledge with Kubota equipment. I'm mechanically capable and can perform most of my own maintenance and trying to get the unit operational again for my kids help out with the grass mowing this summer. A new ZD1211 was ordered and received last year after almost a year wait!!

Ok so the patient is a ZD28 with a left side axle assy that is not driving properly so looking for advise on where to start on repairs. Unit is I think is a first gen unit (no roll bar) approximately 2006. The unit has 20,690 hours and has had regular oil/filter changes on the engine, however I do not believe the HST unit or fluid has ever been serviced!!!!!
I've started the disassembly process and so far have noted the following;
Left side drive axle, dry outer casing without signs of leaks, minimal oil drained approximately 2 tbsp of oil in axle assy when drained, black fluid, minimal particles. Right side drive axle, signs of outer casing with some fluid stains, axle reservoir appeared full, fluid black. Main HST fluid drained, fluid black with some sheen to it, some flakes/shavings found in drain pan. Strainer removed and some shavings found on screen.
Question is whether to try to flush the hydraulic system out replace just the left axle assy, left control valve assy or both? The weird thing is that the unit worked fine (other than a couple of no start conditions in the previous summer) until I went to move it after storage and it would not steer properly.

Hoping someone on here may be able to help provide a plan of attack on this repair as I assume the whole hydraulic system should be flushed prior to part replacements.:oops:
 

GreensvilleJay

Well-known member

Equipment
BX23-S,57 A-C D-14,58 A-C D-14, 57 A-C D-14,tiller,cults,Millcreek 25G spreader,
Apr 2, 2019
11,419
4,908
113
Greensville,Ontario,Canada
1st step, get the WSM... I grabbed one off the web to see what's involved...
2nd, drain and flush, replace filters(screens ?) ,heck it's 20 years old !
3rd , try it and see what happens

Only if it doesn't work right, then tear it apart.....
 
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Spicy Chicken

New member

Equipment
ZD28, ZD1211
Mar 7, 2023
7
4
3
Ontario
1st step, get the WSM... I grabbed one off the web to see what's involved...
2nd, drain and flush, replace filters(screens ?) ,heck it's 20 years old !
3rd , try it and see what happens

Only if it doesn't work right, then tear it apart.....
Thanks Jay for getting back on this appreciate it. I remembered something after I posted this and realized that I had dropped off the unit at a local dealer in spring of '21 for the no left drive issue and to do a full service on the unit for my father in law but had forgotten this. They likely drained the left axle assy which is why there was very little fluid in it :unsure:. They also told me the entire HST unit was destroyed and required complete replacement with an estimate for $12k + 10 hours labor. I know they likely only looked at the left axle assy and threw in the towel as every other feature on the machine functions properly. I had ordered him a new ZD1211 unit (for only a few thousand more than the repair estimate) but the delivery date was TBD due to all the shutdowns everywhere so wanted to make sure I had something that he could use as a buying herd of goats would be out of the question...
I have planned to do exactly what you suggested but was worried if metal particles could have damaged the control valve or anything else in the hydraulic system. I have downloaded the service manual but just trying to get my head around the hydraulic system first. I believe the axle assy's are self contained for fluid. The manual does state that the strainer and hst oil could show debri when changed which seems a little odd to me that it would almost be expected. Right now I'm going to remove the left axle assy and disassemble and repair any damage, then remove the LH control valve to try to determine if there is any debri or damage and either replace or repair it. I am tempted to refill the fluids as suggested if the control valve seems intact, run it and flush again and install a new filter. The old filter is black inside but does not appear to have as many particles as the drain pan does so hoping the hydraulic system is ok???
 

GreensvilleJay

Well-known member

Equipment
BX23-S,57 A-C D-14,58 A-C D-14, 57 A-C D-14,tiller,cults,Millcreek 25G spreader,
Apr 2, 2019
11,419
4,908
113
Greensville,Ontario,Canada
'black' is usually due to old age and heat. Funny how people never seem to clean the cooling fins of mud and debris on HST riders.......
Assuming the oil goes 'everywhere' and the right side workd fine, then odds are the left side will too.
roll the dice, clean a fill, see what happens..
I'm still choking on the 12K PLUS labour..... wonder what a complete machine is worth !
 

Spicy Chicken

New member

Equipment
ZD28, ZD1211
Mar 7, 2023
7
4
3
Ontario
'black' is usually due to old age and heat. Funny how people never seem to clean the cooling fins of mud and debris on HST riders.......
Assuming the oil goes 'everywhere' and the right side workd fine, then odds are the left side will too.
roll the dice, clean a fill, see what happens..
I'm still choking on the 12K PLUS labour..... wonder what a complete machine is worth !
The new one was $19k CAD and took almost a year to arrive so you can understand my WTF response when I received the estimate. I almost cancelled the order on the new one at that point as I had just purchased a gas JD zeroturn for less than the repair estimate and was planning to let him use mine.
 

Spicy Chicken

New member

Equipment
ZD28, ZD1211
Mar 7, 2023
7
4
3
Ontario
Ok so just got back to this machine. I have replaced the HST filter, and refilled the HST and both axle assemblies with new fluid. Prior to this I did remove the LH axle assembly and open up for inspection as this was the unit that did not seem to be working. Everything inside seemed to show little wear and no obvious damage. Reassembled and refilled with fluid.

The problem now is that I do not have either the LH or the RH drive working now. Hoping someone can help point me to the next thing to look at? Do I need to bleed the hydraulic system somehow now?
 

Dustyx2

Active member

Equipment
BX22, M7060, Landpride RC-2512, Woodmax SB84
Feb 19, 2021
217
63
28
NE Wyoming
The actual hydrostatic drive is located in the center section. The axle assemblies are just reductions driven by the hydrostatic motors in the center section. Your pump may be too damaged to pick up oil. I don't know if there is a way to prime it. Is the 20,690 hours a typo? If not, that is incredible.
 

GreensvilleJay

Well-known member

Equipment
BX23-S,57 A-C D-14,58 A-C D-14, 57 A-C D-14,tiller,cults,Millcreek 25G spreader,
Apr 2, 2019
11,419
4,908
113
Greensville,Ontario,Canada
re: do not have either the LH or the RH drive working now.

you haven't got both 'bypass' levers in 'bypass' instead of 'drive' ????
 

whitetiger

Moderator
Staff member

Equipment
Kubota tech..BX2370, RCK60, B7100HST, RTV900 w plow, Ford 1100 FWA
Nov 20, 2011
2,921
1,383
113
Kansas City, KS
They also told me the entire HST unit was destroyed and required complete replacement with an estimate for $12k + 10 hours labor.
If you order part number K3151-98060, you will get both RH & LH pump and motor assemblies, the charge pump assembly, the rear cover for the PTO case, a new input shaft, a new strainer and filter, and some new pressure tubes. The kit is $2750.00 US.
You can totally replace the entire hydrostat system of the mower for $3000.00 plus labor. It is not difficult to do, just takes some time.
 
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Spicy Chicken

New member

Equipment
ZD28, ZD1211
Mar 7, 2023
7
4
3
Ontario
Sorry for the delays getting back on this.
@dusty, sorry the hours noted was a mistake, it is actually at 2,069.5 hours and up until this point has been flawless.
@GreensvilleJay. I have verified both levers are actuating the pumps as they normally do but no motion. I am able to roll the unit however when it is off almost like it is in neutral and it did not move like this prior. My JD has a lever that is used to disengage the HST so is there something like this on this ZD??
@whitetiger thanks for the p/n, I have call in to my local dealer to get pricing and availability. Just waiting on the call back.
Out of curiosity I read through another thread on here and someone mentioned replacing the HP Relief and Check valve"
Where would I find this as I'd like to check this before I order a replacement HST rebuild kit?
 
Last edited:

Spicy Chicken

New member

Equipment
ZD28, ZD1211
Mar 7, 2023
7
4
3
Ontario
Ok I think I know where this valve is located after looking at the manual. I'm going to have a look at this before I go further
 

Spicy Chicken

New member

Equipment
ZD28, ZD1211
Mar 7, 2023
7
4
3
Ontario
Just wanted to close this off and thank all who replied, especially want to thank @whitetiger for the tip on the kit. As I dug into things further it was evident that the LH pump/controller assy had completely eaten itself and spread sharpnel thoughout. I ordered the kit K3151-98060 as noted above and replaced everything, flushed x2 and now have another working machine to accompany the new one. My kids will have no excuse to not get out and help with the cutting now. That reminds me I'm going to need to order another drum of diesel now .....
 
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