ZD21 Hydro Rebuild
- Thread starter fatjay
- Start date
whitetiger
Moderator
Staff member
Equipment
Kubota tech..BX2370, RCK60, B7100HST, RTV900 w plow, Ford 1100 FWA
These hydro's are proprietary to Kubota. Their are no parts available for them. I have probably thrown 20 or more in the scrap pile.
We have found several of them that like your's were cut out by contaminates in the oil. You should remove the charge pump to see if that is where the contamination came from. Also, the charge pump supplys oil to the deck lift and PTO clutch. All that metal in the oil and some gets pumped into the PTO clutch pack which needs dissembled and cleaned. The metal also gets in the bearings for PTO and bevel gear shaft.
You are just getting started with your repair.
That's unfortunate. The cover is K7021-39503 and the gasket is # k7021-39040, both are available from numerous dealers or online sites.
I got all the parts cleaned up. The pistons/barrels had perfect clearances/tollerances. I had a few pistons from the other barrel and used them, and the other ones, and couldn't tell the difference. Put it together with a new gasket. Went together perfectly. Added hydro fluid slowly turrning the lower barrel so it wouldn't be started dry. I drained the trans and changed the filter, filled up with 303 to the top. Hooked it all up and ran it for about 5 seconds. Checked the level, it dropped but not to much. Filled to the top again. Started again, left the cover off and watched the flow. Ran for 2-3 minutes. Tested forward and reverse, fully functional. No leaks at all.
Did a few more tests at low rpm for another 10-15min. In my experience if it's going to go bad from assembly, it'll go bad very fast. Tried to take the cheap way out on motorcycle cams vs lifters once, didn't go well. This has passed my expectations so far, hopefully it holds up to tomorrow.
Tomorrow I'll make a brief few passes, then drain the system and flush with travelers premium. I hope everything stays working well. I cleaned it surgically and reassembled everything with great care. If it works well, I'll buy the add on expansion tank. Until then I'll monitor the fluid closely. I'll run it a bit more tomorrow at low rpm to properly mate the surfaces.
I got all the parts cleaned up. The pistons/barrels had perfect clearances/tollerances. I had a few pistons from the other barrel and used them, and the other ones, and couldn't tell the difference. Put it together with a new gasket. Went together perfectly. Added hydro fluid slowly turrning the lower barrel so it wouldn't be started dry. I drained the trans and changed the filter, filled up with 303 to the top. Hooked it all up and ran it for about 5 seconds. Checked the level, it dropped but not to much. Filled to the top again. Started again, left the cover off and watched the flow. Ran for 2-3 minutes. Tested forward and reverse, fully functional. No leaks at all.
Did a few more tests at low rpm for another 10-15min. In my experience if it's going to go bad from assembly, it'll go bad very fast. Tried to take the cheap way out on motorcycle cams vs lifters once, didn't go well. This has passed my expectations so far, hopefully it holds up to tomorrow.
Tomorrow I'll make a brief few passes, then drain the system and flush with travelers premium. I hope everything stays working well. I cleaned it surgically and reassembled everything with great care. If it works well, I'll buy the add on expansion tank. Until then I'll monitor the fluid closely. I'll run it a bit more tomorrow at low rpm to properly mate the surfaces.
One oil change from the premium, went to mow a around the yard and circulate the fluid real good, then did another fluid change. Took it over to my fathers to mow a bit. He took it for a spin, not bad for a first time operator. Ran perfect, just a couple things need adjusting. The throttle cable needs lubed, grease points greased, the deck wheels need adjusted. Nothing major though.
One thing has to change, the R4 tires need to go. Tight turns dig in and ruin the lawn.
One thing has to change, the R4 tires need to go. Tight turns dig in and ruin the lawn.
That's the thing, I wanted a zero turn for a long time but I couldn't justify the expense. This one was $500, though, so definitely worth it to repair I think.
I think that was the best deal since the Louisiana Purchase. The mower looks like it was stored inside and not abused (no obvious dents).
I'd suggest checking the transmission fluid strainer for chips after 50 hours just to be sure nothing else is self destructing. If you find chips, clean it and check again after 50 hours. When chips stop showing up, revert to scheduled maintenance.
If you experience hot starting problems, I'd recommend installing the starter solenoid heat shield from a ZD1021. You clearly have the skills to do it and it stops the exhaust manifold from cooking your starter solenoid.
I'd also recommend over filling the transmission with fluid. I fill mine to within a couple of inches of the fill port. Mine has 1,600 hours on it and the strainer has been chip free. I considered getting the auxiliary tank but by the time I learned of the potential problem my mower had well over 1,000 hours on it chip free, so I just started over filling it and went back to mowing. We have a relatively flat yard.
Fitch
Where is hte strainer? I replaced the filter but I haven't seen this strainer people speak of. I've flushed 3x with an hour of run time between flushes.
I've filled it to the top every time. I noticed that if you add the extra canister, it's filling it to the top anyway, so I figured it'd be no harm in doing so. It overflows a bit when I start it and run it, but then it settles down about an inch from the cap, so I figure that's the sweet spot, but still 1-2 inches above the "full" line on the dip stick.
I've filled it to the top every time. I noticed that if you add the extra canister, it's filling it to the top anyway, so I figured it'd be no harm in doing so. It overflows a bit when I start it and run it, but then it settles down about an inch from the cap, so I figure that's the sweet spot, but still 1-2 inches above the "full" line on the dip stick.
The strainer is in the very bottom of the case. There is a large hex bolt that screws through a line, at the bottom/back of the transmission, 27mm hex if I remember right. Once loose, ALL fluid will come out-so be prepared to catch it. The strainer is attached to the "bolt". Just pull it out.
Fatjay, you said "One thing has to change, the R4 tires need to go. Tight turns dig in and ruin the lawn."
Before you go out and replace your tires, mow for a while at a slower pace and get use to turning.
We've had Grasshopper mowers for several years and my wife does ALL the mowing. She complained initially about the divots the tires made when turning. She's a cosmetologist and one of her regulars owned a lawn care service. She'd pick his brain ever time he was it about how to do this, how to do that.... She'd come home and be excited 'cause Kenny came in and got a hair cut. Then tell me the technique he told her, then go right out and try it.
We never changed tires. New machine last fall, same tires! Yard looks NICE!
I'm suggesting you need a good coach!!
Before you go out and replace your tires, mow for a while at a slower pace and get use to turning.
We've had Grasshopper mowers for several years and my wife does ALL the mowing. She complained initially about the divots the tires made when turning. She's a cosmetologist and one of her regulars owned a lawn care service. She'd pick his brain ever time he was it about how to do this, how to do that.... She'd come home and be excited 'cause Kenny came in and got a hair cut. Then tell me the technique he told her, then go right out and try it.
We never changed tires. New machine last fall, same tires! Yard looks NICE!
I'm suggesting you need a good coach!!
Daren Todd
Well-known member
Lifetime Member
Equipment
Massey Ferguson 1825E, Kubota Z121S, Box blade, Rotary Cutter
Burn outs are common when first using a zero turn 
Wife and I had the same issue with ours when we first got it with the turf tires. It's just a matter of slowing down on sharp turns and feathering the controls.
Wife and I had the same issue with ours when we first got it with the turf tires. It's just a matter of slowing down on sharp turns and feathering the controls.I don't think the problem is speed. I think I need to get comfortable with setting the rear wheel in actual reverse when the other one is forward, that way it's not completely stopped when making those hairpin turns, so it doesn't sit in one place and grind.
Still I have a lot of obstacles in my yard, lots of tree's to mow around, thus my wanting the machine over my old mower. Definitely nice not having to make 3-4 passes in a single tree. My lawn looks brilliant, the cut is perfectly level with no scraping in the little hills, despite being a 60" cut.
Still I have a lot of obstacles in my yard, lots of tree's to mow around, thus my wanting the machine over my old mower. Definitely nice not having to make 3-4 passes in a single tree. My lawn looks brilliant, the cut is perfectly level with no scraping in the little hills, despite being a 60" cut.
So I know it’s been a while since your post but I have my fingers crossed here. I believe I’m running into the same issue and this thread has been tremendously helpful. Did you ever add the hydraulic reservoir? If so is there anyway you might still remember where I could find one? I’m afraid I’m about to have to drop $3500 to repair mine and then not even have gotten to the root of the issue without the reservoir. Fingers crossed you see this!
whitetiger
Moderator
Staff member
Equipment
Kubota tech..BX2370, RCK60, B7100HST, RTV900 w plow, Ford 1100 FWA
fatjay has not been on the site since Aug 2022, so he probably will not answer you. The reservoir is available from any Kubota dealer. The kit is part number K3111-9860-0.