EXPLAINED: How a Hydrostat Transmission Works

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!

[pgr]

Great video for explaining how the hydro transmission works. Thanks.

[williamnewsome]

Great job explaining how the transmission works.

[chrisallen]

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.

[curtklemenz]

Excellent video, especially the warning about grease shaft u joints.

[chrisj.]

Great video and very informative. Thank you.

[altonrowell]

Good video thanks for the information.

[tsesko]

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

[scottstout]

Hey man great video. Do you have one on how to tear down the transmission and replace the shaft? Thanks

[broncobart]

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.

[stoneyswolf]

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

[xx]

Hi, i got a old Yard man 12.5 L head opposed engine with 8 speed "control" but it moves perfectly about mid speed and no noise BUT the speed control is doing zip when i move it fully F & B is the linkage broken or the fluid low?? as it moves crisp and normal in forward and reverse gear. No slip when i let clutch out, seems normal except no speed change with that lever.

[truthhurts]

Well glad I just missed out on that tractors

[altonrowell]

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.

[ModernSurvivalists]

If you have a JD2320 make sure you grease those ujoints!

[CalebGibbsAvenue]

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.

[rrud]

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.

[joelcordier]

Isn't it possible to add a kind of rubber seal like in car transmission ?

[wbrockstar]

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

[michaelmilligan]

What type of hydraulic fluid did you use to refill it an do you use the same fluid for the axle part

[jacobhendrickson]

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.