Kubota's Zd28 Hydrostat Modification Fix Kit

Discussion in 'Lawn Mowing' started by Grass Man, Oct 20, 2006.

  1. Grass Man

    Grass Man LawnSite Senior Member
    Posts: 272

    KUBOTA'S ZD28 HYDROSTAT MODIFICATION FIX KIT (1 of 6)

    .... This is what the Kubota dealer told and implied to me. The failure of the Kubota ZD28 hydrostat is caused by mowing on hills, apparently pretty good sized ones at that. What happens is that the squash plates (for the lack of a better name) become starved for oil and the machine sucks in AIR and apparently prematurely wears out the contacting squash plates which are supposed to operate in a constance pool of oil. The fix is, to replace the hydrostat's flexible filler cap with an expandable air tight screw down cap (see pic). Remove the hydrostat's DIP stick and replace it with a small right angle elbow (see pics) Install a white plastic-like recovery bottle just under the fender and on the mower's right side (see pics). Connect the small right angle elbow with a small rubber-like hose to the recovery bottle (see pics). Also, I was told that the threaded screw-in filter screen was removed and checked and the fluid in the hydrostat was replaced. During operation, when the hydrostat needs oil, hill or not, it sucks the oil, rather than air, that it needs now from the recovery bottle into the hydrostat. Now, the implication is, with this fix the problem goes away. This is all the information I have on this problem at present.
    .... I personally spent a couple of years talking and demoing, when I could, to all kinds of associated people plus the very good and positive experiences I have had with my own Kubota tractor “L” series before purchasing. Yes, I distantly heard early on that there was a hydrostat problem, but I also heard that problem had been fixed and then they doubled the warranty from two years to four. And it was after this consideration that I made my proud purchase of my new ZD28. Then I started hearing more people having hydrostat problems with very low hours. It was at this point, I, and I am sure some Kubota dealers, also became concerned, especially when I heard that wheel motors were $2500.00 per side. I still have confidence in Kubota, but at the same time I don't want to get stuck with a very expensive lawnmower that won't mow.
    .... What is your feeling here. Do you feel that this dealer installed modification fix kit will resolve this problem? Are there others as concerned as I am about their mowers? Do you feel that if your mower has low hours but many years that Kubota will stand behind their product with this problem? What are your thoughts?

    P1000306 ZD28-1 fix.JPG

    :)

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    P1000306 ZD28-1 fix.JPG
     
  2. Grass Man

    Grass Man LawnSite Senior Member
    Posts: 272

    Grass Man]KUBOTA'S ZD28 HYDROSTAT MODIFICATION FIX KIT (2 of 6)

    P1000308 ZD28-2 fix.JPG


    :)

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    P1000308 ZD28-2 fix.JPG
     
  3. Grass Man

    Grass Man LawnSite Senior Member
    Posts: 272

    Grass Man] KUBOTA'S ZD28 HYDROSTAT MODIFICATION FIX KIT (3 of 6)

    P1000309 ZD28-3 fix.JPG

    :)

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    P1000309 ZD28-3 fix.JPG
     
  4. Grass Man

    Grass Man LawnSite Senior Member
    Posts: 272

    Grass Man] KUBOTA'S ZD28 HYDROSTAT MODIFICATION FIX KIT (4 of 6)

    P1000310 ZD28-4 fix.JPG

    :)

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    P1000310 ZD28-4 fix.JPG
     
  5. Grass Man

    Grass Man LawnSite Senior Member
    Posts: 272

    Grass Man] KUBOTA'S ZD28 HYDROSTAT MODIFICATION FIX KIT (5 of 6)

    P1000311 ZD28-5 fix.JPG

    :)

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    P1000311 ZD28-5 fix.JPG
     
  6. Grass Man

    Grass Man LawnSite Senior Member
    Posts: 272

    Grass Man] KUBOTA'S ZD28 HYDROSTAT MODIFICATION FIX KIT (6 of 6)

    P1000312 ZD28-6 fix.JPG

    :)

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    P1000312 ZD28-6 fix.JPG
     
  7. specialtylc

    specialtylc LawnSite Bronze Member
    Posts: 1,656

    I think youre dealer is feeding you a line of bull. I bought a ZD21 five years ago. At 170 hours the trans started acting up. Many of the early production units like mine were made with a bushing on the input shaft to the pump from the engine. Some of the bushings wore prematurly, causing excess play on the shaft seal, which allowed the pump to suck in air. The factory sent a complete trans assy to the dealer, which was a later production version which has a regular bearing on the imput shaft. I have over 2000 hours on this mower now and never had another problem since. This spring I bought a New ZD28 , it now has close to 400 hours on it and has been a perfect running machine. My 43 hp Kubota tractor with a hyd trans has been a perfect runner also.
     
  8. Envy Lawn Service

    Envy Lawn Service LawnSite Fanatic
    Posts: 11,062

    Well..... boy do I want to get into this???

    Oh alright, here goes. Specialtylc is correct that there was a problem with the input shaft bearing, which caused air to draw in.

    It is also true that the more recent failure were due to problems with the squash/swash plates. As I understood it, from a tech friend of mine that personally repaired several, and as far as I know was also the one to 'diagnose' the issue..... the problem was that once the transaxle was torn down for inspection, the problem found is that these plates were not properly machined on the mating surfaces.

    It's true that where these plates meet is 'wet' and this improper matching mating surface caused some mechanical issues (maybe clatter/chatter/shimmy ?) and what would happen is that this issue would cause CAVITATION in the hydro fluid. This is like air, but not exactly, because cavitation moreso seems to "manifest" as voids or pockets forming down in an oil bath... and no air is needed. I guess air or vapor makes it's way into these voids as the fluid cycles (?)

    But the point is, air, vapor or just voids, the result is still the same. No oil means no lubrication and metal to metal contact. The longer the machine runs and the hotter it gets, the more it acts up, the more damage is caused and the closer it is to total failure.

    Also, as I understand it, the only true fix for this problem is either to replace the entire effected transaxle or tear it down completely, completely flush it, replace the effected plates and put it back together.

    I was also told that Kubota tracked this back to the manufacturing process of these plates. As far as I know this has been corrected and Kubota has been covering problems under warranty. After the first few my friend repaired, Kubota started just sending him new hydro units from an unaffected MFG lot. I guess it was about as cost effective and much more reassuring for the customer. None of the ones he has repaired by either method have been back with more problems.

    As for your dealer's fix.... I'm not sure what to make of it. I don't know if this is a fix for a similar related, but different issue, or if this is a cheap "band-aid" fix in an attempt to extend the life and avoid expensive warranty repairs.

    When I look at his fix, the things that come to my mind are...
    - How do you check your fluid level now?
    - Will the hose clamps and reservior bottle hold up if any pressure is involved?
    - How hot does your hydro fluid get and can the bottle withstand it?

    I'm sure this would help some, but how much is debateable if it is indeed a band-aid fix. The reason I say this is understand that cavitation can "manifest" down in the flow or down in the oil bath without introduction of foreign air. Also understand that when fluid cavitates, the voids take up space in the system and therefore the oil level rises and as the oil gets hotter it expands more. Once all the head space is filled, the pressure will push the fluid out of the stock vented cap, or possibly around the dipstick too.

    His fix would indeed help you NOT loose fluid, just like your engine cooling system reservior bottle does... same concept. It might also help reduce the introduction of air. But I'm not so sure about that really, because when the machine is 'normal' what is in that reservoir and those hoses? AIR. Likewise, I'm really not so sure this fix wouldn't make it easier for the system to push out NEEDED oil into the reservior... oil that's needed for lubrication in the system.

    So overall, it is really hard to say.
    I'm not sure it's good or bad, but coming from a dealer, I would feel uncomfortable about it if it were my machine. I think I'd want more professional input than just what one dealer says. I'd want some fact-based explaination and more people than him telling me this was the right thing to do.
     
  9. zd21man

    zd21man LawnSite Member
    from nc
    Posts: 21

    Grassman ,I own a zd 28 and was wondering about this four year warranty.I ask my dealer and he said one year commerical and two for home owner.I have not had any trouble yet .But starting to get a little worried with whats going on with the other kubotas.Thanks.
     
  10. tomo

    tomo LawnSite Senior Member
    Posts: 660

    Hello, Kubota zd28pro very nice machine but and it is a big BUT........ALL THOSE PEOPLE WITH A GOOD TRANNY """GREAT''' As i was close to buying one there seemed to be one to many horror stories 4 me .Purchasing another mower as a result .
    As i mentioned great to the people who have a succesful unit. My advice to myself and others would be as follows :: as i spent many years in the mechanical industrial i learnt that many makers have issues with transmissions.

    .1/ tranny issue
    2/different oil in this case up to 4 diff ones ,running in oil , warranty oil , problem oil , generic castrol
    3/trans kit stage1 stage 2 stage 3
    4/ full overhaul of tranny
    5/ any combination of above
    6/ dealer excuses or bad info either at start or during your experience
    7/eventually tranny has major redesign and fitted in production run
    8/ in a model update tranny is eventually changed to a good design, completely different to original.
    9/ the sad part is the trannys that did not fail were let go with cust unaware of issues...........this typically was ok for some limited time but trannys eventually failed and well prior to the competition.Typically cust gets caught with a lemon and a poor experience.At this stage they r out of warranty.

    10/ although i will not disclose tranny maker i think most people get the idea . [not in the mowing industry]
    11/ this particular machine maker had a tranny rebuild section in there main factory ,very very weird !! This lemon tranny was costing them big time !!!!!!!!!!!!

    11/ as i said if u have a good tranny great but i will pass on this occasion.
    ps next generation of zd 28 pro interesting but i most likely will have a diff mower.

    TOMO:waving:
     

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