EXPLAINED: How a Hydrostat Transmission Works
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- Опубликовано: 4 июл 2024
- I show how a hydrostatic transmission drive unit works on a John Deere 2320 HST compact utility tractor. This unit had a drive-shaft u-joint failure which broke the input shaft to the hydrostatic drive transmission.
The hydrostatic drive is divided into two portions, a variable flow pump controlled by a swash plate, and a fixed ratio hydraulic drive motor.
The forward / reverse speed of the tractor is controlled by foot pedals, which are connected by linkage to the swash plate in the drive pump. This controls the direction and flow rate of hydraulic fluid sent to the hydraulic drive motor.
The hydraulic drive motor is forced to turn in either direction based on the flow rate and direction of the hydraulic fluid. The motor will also hydro-lock on the fluid when there is no flow, causing the drive motor to also work as a brake.
If you have one of these JD 2320 tractors, be sure to check your driveshaft u-joints and keep them greased! 
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Thank you for making this video, great explanation of how a hydrostatic pump and motor works. On the dry axle issue, maybe a solution is to fit something like a Scott Oiler - it's a system that automatically lubes motorcycle chains but something like it fitted to those dry points might help.
Great job explaining how the transmission works.
Thank you!
Great video for explaining how the hydro transmission works. Thanks.
Great video and very informative. Thank you.
Excellent video, especially the warning about grease shaft u joints.
Thanks 👍
Good video thanks for the information.
Excellent. Thank you!
Nice video
Well glad I just missed out on that tractors
thank you
You could always take that drive shaft to a drive shaft repair shop and have them make you a brand new drive shaft with different u-joints that are sealed from the factory like automotive style you joints
Probably a good idea for anyone with this tractor.
Great video - crazy engineering
It sure is!
Actually used to work for Deere. Had a 1023 come in for the same failure. Somehow that grease zerk fitting was omitted from the owner’s manual. Deere eventually issued a PIP for it after enough owners with low hour machines experienced failure.
Thanks for the info
I have manufactured every single one of these parts and seeing this gives me ptsd lol. My dad ran the machine shop, his guys made all of the prototypes for these before they went to production
Thanks for commenting! Would love to hear your thoughts on the U Joint failures.
That drive shaft should be like a Honda goldwing shaft. It's completely inclosed in a sealed housing. No water no dirt can get to it.
Van you think of any reason the rotation of the pulley put in reverse the pump works otherwise I have some flow of oil but no power to the drive.
This is the 5th time taking it off ad priming everything perfectly.
But can't get power unless I rotate the pulley backwards. It's not supposed to rotate that way plus no way to reverse it ...that would not work anyway. I'd take it apart again but I can't think how thats possible. I just fix all the issues now this happens it worked fine before.
Hey man great video. Do you have one on how to tear down the transmission and replace the shaft? Thanks
Thanks! Sorry, I didn't film the entire process because I short on time.
Isn't it possible to add a kind of rubber seal like in car transmission ?
If you have a JD2320 make sure you grease those ujoints!
Nice.👌🏻👌🏻
Just started tearing a 2320 apart today, that drive shaft broke off at this " stub shaft " . I changed the drive shaft last year at 800 hours because the engine side ujoint on the shaft broke apart. So I'm not sure why the stub shaft snapped this year. Anyway, I really appreciate your video.
Sorry to hear you had the same issue. The one I fixed only had 200 hours which seems way early for a u-joint failure. The splined stub of the transmission input shaft had snapped off when the broken u-joint allowed the shaft to start flailing. If your u-joints were still good on the second failure I wonder if it might have been partially fractured from when your front u-joint went out. These spin at engine RPM, which is higher then a typical PTO shaft, drive shaft, etc. Lots of forces when they start flailing, especially if the tractor is at full throttle like is typical for mowing, etc.
@@ModernSurvivalists lol you said it, I was running a power broom in the snow when it snapped. It was like I hit an IED! So when the first ujoint failed last year, it was all rounded off like the one in your hand was, so it actually still ran just with a lot of vibration . I think it ran Like that , vibration and shuddering for a long time, and after I replaced it, the next weakest link was the transmission side. That's my theory anyway
Oh and I had a question, do you know where I can find torque specs for a project like this? Besides the dealership?
@@rrud59 I wasn't able to locate any torque specs online either. I did refer to the exploded diagrams you can find for part numbers and to assist me with the teardown. I just torqued it similar to how I would a engine case. First put in all fasteners finger tight, then tighten them snug in a cross pattern working from inside to outside.
@@rrud59 Also - in order to remove the hydraulic drive from the transmission case I had to cut out the round crossmember tube welded in the frame. I used a sawzall and welded it back in once the transmission was all back together.
My 2305 is about the same, very hard to get to the front grease fitting.. I've only been greasing it once a year, maybe I should go for 2x..
My HST has another issue that maybe you have some insight on.. JD and the local shop are no help whatsoever.. I feel my HST is getting way too hot, up over 215F at times using the belly mower. It has about 700hrs on it and I've been pretty strict to the maintenance schedule. I've hit something twice in tall grass that stopped the tractor (belly mower doesn't have much slip I guess) with some resulting fair amount of grit on the fluid filter when I did the change. I've since started only mowing till the temp around the fluid level window reaches 180 (about 30-45 mins), then I stop till it cools. This is with outside temp in the upper 70's. Speed of the tractor seems a little slower than new, but not significantly. Any ideas? Maybe a restriction, worn parts, something warped?
Sorry just saw this comment. I am not sure on this one. If there is a cooler for the HST fluid (I can't remember and don't have one here to check) make sure it isn't obstructed and any fans / belts etc. are functioning.
Great info & explanation.
Are any parts that are inside/attached to the housing you were discussing used for/by the pto system for blade engagement or is the hydrostatic system used solely for the mowers forward/reverse/speed application only?? Thanks
On this model I believe it is for transmission function only. The variable swash plate pump will only generate flow with pedal input (by design). Some hydro transmissions do have a small auxiliary pump that can be used for raising a mower deck or power steering etc. Larger equipment with bigger hydraulic needs will usually have a dedicated gear driven pump for those circuits.
@@ModernSurvivalists
Ok thanks again for another great explanation to a additional question.
That is absolutely insane to put grease fittings like this where you can’t even get to them. I’ve heard of these failures being much worse than just that shaft but also taking the trans case with it. Huge failure.
How to change bearings n back tires craftman 16 horse overhead valve
That appears to me as the hydrogear bdu21 hydrostat
What would Cause when you press in the clutch pedal to not disengage the hydraulics ?? is something broken inside
It would depend on the equipment - on many machines they have hydraulic pumps that are driven directly via the engine gear case and do not disconnect with the clutch & transmission.
I have a yanmar 425 hydrostatic transmission 4x4 not working why??
Can that stub be replaced without having to disassemble the whole transmission
Unfortunately I don't think there is any way to remove the shaft without splitting the pump case.
What type of hydraulic fluid did you use to refill it an do you use the same fluid for the axle part
This was a very low hour machine so we opted for the expensive JD stuff. I can't remember which, but I think it called for the low viscosity version.
They probably left a greasing time periods out of the manual because it would deter people from buying it sounds like a problem with the build and should be recalled
Agreed. Whole damb thing should be recalled. Such bad luck with 2025r. They even left the same crap design for the u joints. No easy way to grease. That's the least of this things issues.
Hey I've got a question on my hydrostatic I have forward but no reverse does that make sense to you and it's on a Parker heavy duty integrated hydrostatic system.
I sure would appreciate any help
Not familiar with that unit, but many of them have a bypass / pressure relief of some sort than can be engaged to free-wheel / tow the machine. Sometimes just a lever, or a bolt you turn. It allows the fluid to the drive motor to bypass in a loop so that the output shaft can free-wheel. I am wondering if maybe that could be related to your issue?
@@ModernSurvivalists Thanks, I took it apart and found the tiny nut on the Reverse poppet valve came off and the spring backed off. Also there were 3 tiny pieces of metal inside the pump barrel. I think from the pump springs. This metal scored the port plate and bottom of the barrel so I am replacing those and reinstalled the nut on the poppet valve with lock tight. Keeping fingers crossed.
@@mountainmike1685 Glad you got it figured out!
@@ModernSurvivalists Thanks!, I hope your video and other conversations help other folks fix their own equipment.
Anyone know why these u-joints seem to lose their grease so fast?
MY 2320 did not have grease fittings. I have found and replaced the u joints that have greas fittings.
What's the RPM of the shaft?
Runs at engine RPM - driven directly from flywheel. @@Gareth96v1
Great video. I have a question you might be able to help with. I have a 1990 Ariens tractor that is have a issue. The mower wont move forward and make a whining sound...it move backward strong and fast...just not forward. The belts seem to be tight, the fluid seem to be full, the linkage seems to be moving. The mower is in super good condition and hope to save it. Any help would be great...Thanks
I'm not a hydrostat trans pro, by any means. But, used to rebuild lift trucks.. gas, diesel, hyd pumps, motors, cyls., etc.
Im about to pull my 1st JD stx 38 hydrostatic trans apart, so I was digging around for info on my John Deere. I got it for free, and ran great, but had weak trans. Only cut grass twice, and it won't move now.
I'm not paying $700 for a used trans. So grass can grow, until I receive carb kit for my mower, or find a trans rebuild kit for this.
Mine won't move, and whines, in either dir..
Im not sure what type of trans you have..
If yours is moving in Rev, solid and strong, but nothing at all in For. , try checking all the linkages.
Basically, pump Pushes oil one direction or the other. If Rev is good, charge pump, creating the oil pressure, is good. Charge pump makes pressure. A valve or radial pump gives you direction. .
. In your case, oil is not going to forward direction, but you have Rev. You have pressure, it's just not going to forward.
I'd check all linkages, make sure the valve, or actuator is traveling all the way in both directions, nothing is loose, or stuck in them. Make sure there's not a problem with a neutral switch or anything. If there's a neutral safety switch, and it's misaligned, it may stop the fluid when trying forward.
If it's anything more than that,, you may need a shop.. Again, sorry I can't be of more help. I know the theory behind it,, and I'm able to find problems once I have a machine apart, and I can see things, but,, i Don't have enough experience with them, and can't give you the direct answer.
. Maybe this will give you some clues, help you figure it out. Good luck.
Shop rates must be insane right now, hope you can fix it.
If it's your hydrostat may as well haul it to the junkyard and get what you can out of it.
Hydro transmissions on lawn mowers was the dumbest idea anyone ever came up with.
Sad to say from the description of your problem it does sound like it's your hydrostat transmission. Father had a husqvarna that did the same thing. Would go backwards but not forwards till you got off, yanked the mower backwards a ways then it'd make a few laps around till the forward gears locked up again. That mower wasn't even much over 5 years old when it started doing it either. He parked it and got a regular transmission murray. Sad to say murray's went out of business a few years ago.
@@danielsmit11 ya, I second that.
I'm second guessing rebuilding mine. $300+, just for kit. I have to pull it, disassemble, make sure housing itself isn't bad or worn. Starting to think it's not worth the kit or the time to rebuild it.
I've never been a fan of hydro trans. It's nice when it works, but don't seem to last long, and if you have inclines on property, it'll just cause more abuse.
Sad, because last owner of mine,, job ust rebuilt mower deck, and engine has low hours, but $300, is a lot to put into a mower, and it'll still be a hydrostat.
Thinking about grabbing a 5 speed manual with blown motor online, but that's a lot of work also. Take into account all the time needed to change it, probably not woth it.
Maybe I'll pull the 13hp, try selling deck online, since it was just rebuilt, and scrapping the rest.
It's really not worth anything once a hydrostat trans goes.
If all belts are good, shift linkage and free motion piston is free and set properly, it's your trans.
Take the loss, get rid of future head aches, and get one with a manual trans.
That way, its only a clutch or belt, when things go wrong.
@@chrisludston1455 sadly pretty much all have opted to go with hydro stats now. Only one I've seen with a regular trans was a smaller craftsman at lowes, believe it was a 32 inch deck even larger craftsman's above that had garbage hydro stats.
It should be used on Hummer or humvee because humvee has large bump where transmission shaft and gearbox and disel tank remains and inside no space for luxury seats , I want to use only hydro lines to power rear wheels so that car floor can be flat .
I have a forward and backwards one don't know why it doesn't work 😕 any ideas
Do you mean you have forward, but no reverse - or vise versa? If so, both directions use the same pump / drive just push the fluid in the opposite direction, so I would check your linkage between the pedals and the swash plate. Might be as simple as a missing linkage pin! Hopefully : )
@@ModernSurvivalists the inside of the shaft had shifted. There was a screw inside that holds a coupling it pushed it way back.
I just had that stub break on my tractor any idea of how much it costs to fix
I did the repair for a farmer that's local to me but I don't have any idea what most shops or the dealership would charge. It's not a quick job unfortunately.
About how many hours does it take would you say?
A lot.
JD engineering: Artfully manipulating their customers to stop servicing their own machinery. The ultimate goal is a service industry where you never own a JD machine, you subscribe to a service.
John Deere I avoid not that they are not good machines great machines but the company needs to be stopped it as began to crap on the consumer
Damn right! JD sadly has to get their act together. This is what I would expect from Chinese quality. My Lawn Tractor has had several faults that shouldn't have happened. Seat quickly fell apart, plastic hood cracking like an eggshell even though it's kept out of the sun, steering linkages are pitifully small, seat suspension rubbers crumble very often. The only good part about the machine is the Kawasaki engine and the Tufftorq transmission. Never JD again! It's also damaging for American manufacturing. Kubota for me next time. Good Japanese quality.
@@erichmacho5741 thank you for the reply Erich im sorry your machine went that way. My father spoke of JD getting to big for their own good all the way back in the 80s. He strongly supported massy Ferguson not as a single company, but a smaller manufacturer. The whole JD culture planted seed for today where if 3rd generation has parents and grandparents backing the product. They automatically want to buy JD because it’s familier. I can’t blame the consumer we all
Like to think our elders are actually wise. The thing is their is laws to protect a consumer. Congratulations on expressing and forming a solution to your, own needs. I fully support your decision to buy Japanese machines. The job don’t wait just because the machine is down!
This is where the design team has to separate from cost of production staff. Stupid designs usually win out because of cost to produce. Sad really., because a good product with horse crap cheap to produce out the door ideas win.$$$$
i would never buy any john deer. they are all about getting your money, ask any john deer owner
What manufacturer would you choose then
Garbage😢
Hydrostatic transmissions are garbage. No reason for them on riding lawnmowers in the first place.
Hydro is superior in almost everyway to a Gear Transmission for any lawnmower. Just do your homework and buy a good one. True for everything.
@@MikeThomasNYME nah. Hydros suck. Had a Husqvarna with hydro transmission crapped out within a couple of years. Wheels would lock up going forward and had to keep getting off jerk the lawnmower backwards to get it going forward again. Junked that lawnmower quickly and went back to Murray and troybilt.
No need for hydro in a lawnmower, tractor...eh...maybe
@danielsmit11 That's because Husqvarna and the other cheap big box brands put cheap hydro transaxles in their machines because consumers just want something to be pretty and cheap. They use transmissions like the Tuff Torq K46 which is too small and weak for the 25hp tractors they put them in. K62 and larger hydrostatic transaxles and old peerless 15 hydros are nearly indestructible and last for decades.
@@MikeThomasNYME I'll stick with Murray's or troybilt. Have never had transmissions go out on one and have had them last for decades with little maintenance done.
@@MikeThomasNYME like I said there's no need for hydrostatic on a riding lawnmower. A tractor maybe but even that's a toss up