wrong oil

I have got a old 1990 or older john deere 185 hydro trans lawn mower, it got to where the thing would not pull its self. its so old it don't have a trans filter. I changed the trans fluid good old f type red after it got warmed up same thing . got to looking on the jd sights ;[it had the wrong fluid in it] jd recominds 20-50 in the older hydrostatic drive units, puts some Valvoline 20-50 in it like a new trans know, good reverse and every thing. it had red fluid in it when I got it so that is what I put in it to start with.poor older man gave it to me he said it worked good below 55 degrezz ps it 85 here and I have run it for 1.5 hours still working good

hydrostatic transmissions are picky bastards, use type F transmission fluid, or honda hydrostatic trans oil (same stuff)

I would never run ATF in a hydrostatic lawn mower transmission. If anything, you want to start using thicker oil as things wear. The hydrostatic transmissions are simply axial piston pumps with a swash plate used to controll flow and forward/reverse. The motor is simply the same with but with a fixed swash plate. The pistons and the valve plates will wear with age and use and start leaking as the oil gets hot and thin. Using a thicker oil will help lessen the leak.
Most of the JD lawn mower transmissions spec either 10w-30 motor oil or JD hy-guard (depending on the model) Most all of the JD's made in the last 10 or more years have sealed "non servicable" transmissions. Once they start getting weak, you have two choices, either replace it with a new one, or remove it from the machine, knock out a plug on the top, turn it upside down to drain it and then put in a thicker oil. Sometimes thicker oil helps, sometimes not. Most customers either buy a new trans or junk the machine, expecially since we can not gaurentee putting in thicker oil will fix it 100%.
I deal with this every day, I am a service tech at a JD dealer.

a little late to the table but i have a 1986 jd330 lawn and garden tractor and it has a hydrostatic transmission. i use jd hyguard and a screw on transmission filter from napa. the john deere hyguard is a very high spec fluid quality wise. i Change the trans fluid yearly and have never had any problems.

wish mine had a filter. it is still working with 20-50 w oil. is that jd fluid red?

the jd fluid is clearish yellowish. maybe you can put in an inline filter for the trans.

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I would never run ATF in a hydrostatic lawn mower transmission

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Interesting. Any idea what weight the JD Hy-Gard oil is? My Bolens H16XL is using ATF in the Eaton 11 hydro drive (speced in manual) and the older 1256 is using 5W20 although the book specs ATF for the Eaton 10 drive. I try to be religious about keeping the cooling fins of both transmissions clean in the hopes it will prevent the oil from becoming too hot.

If I am not mistaken, I believe I remember reading in a service manual at work that hy-guard is rated at about 10W-30. There is also a low vis version that I think is probably around 5W30.