I have a 2001 GT235 with the K71 transmission, and here's what the manual says:

"Use John Deere Low Viscosity HY-GARD (J20D) transmission oil to reduce transmission noise.

This machine is equipped with an internal wet disc brake transmission. Use only Low Viscosity HY-GARD (J20D) transmission oil. Do not use type "F" automatic transmission fluid.

John Deere Low Viscosity HY_GARD (J20D) transmission oil is specially formulated to provide maximum protection against mechanical wear, corrosion, and foaming. It may be used in all operating temperatures."

I don't know enough about oils to say whether there is an appropriate substitute. I looked on the bottle of Hy-Gard I have, and it doesn't say anything about any standards (like you would see with motor oil such as "SJ"). If it did, then it would be easy to figure out if there was a good substitute.

Sounds like JD black magic to me - a magical way to make sure you buy their high dollar tranny fluid. Under federal law, a manufacturer cannot require you to use their oil, etc. to maintain your warranty unless they provide it free of charge.

Chances are if you bought some Cub Cadet or Sears low viscosity tranny fluid, it would be fine since they use TuffTorq trannies in some of their models also. But who knows. If it was me, I'd wait until I could get to the JD dealer and buy some Hy-Gard so I'd sleep better at night.

If the fluid says it meets the JD spec then you are probably OK. Lots of cheaper fluids won't, however. It might not make a lot of difference in a hydro, but Hy-Gard has a lot of additives that quiet wet disk brakes and extend the life of the JD wet clutches in the ag tractors.

I would make the effort to purchase the recommended fluid, an hour + isnÂt all that long in consideration to hours of frustration in making a poor decision. When I changed the Hydro filter on my CC GT 2542 last summer I went a bought the right products, from a dealer even if it did cost me about 10 dollars for a quart that I used about 8 onces from and I believe 14 or 15 dollars for the filter.

Your GT235 manual is online at JohnDeere.com

4. If oil is low, remove oil fill cap (B) and add John Deere Low Viscosity HY-GARD J20D transmission oil to bring oil level to the FULL line.

Here is a link that might be useful: Manual GT235 - transmission

Way late to the party but anyone else looking for this info . . . you really need to use the LowVis hydro oil. You won't notice any difference at first with the heavier oil but it will eventually blow out the seal in the blade clutch and/or damage the hydro pump.

Make sure you only use the JD-20C Low-Vis oil as noted in the other posts the wrong oil will cause all kinds of problems. If you can't find the oil localy let me know and I can sell and ship it to you.

Hold on - there is a difference between J20C and J20D specs. J20D is the low viscosity spec. If you do not want to use the Hy-Gard you can use any others that meet the J20D spec. Shell Donax TDL and Chevron All Weather THF are 2 that come to mind - but, you won't find them at Walmart, Home Depot, or TSC. You'll most likely have to go to a oil jobber and buy a drum or at least a case of gallons. For me, it is just easier and cheaper to get the Hy-Gard at the JD dealer. YMMV.

Tuff Torq used to recommend ordinary 10W-30 motor oil in their transmissions - the K71 lines. These trannys were found in Simplicity and JD alike. Tuff Torq is now recommending 5W30 synthetic oil. You can buy most of it at auto parts stores, or Tuff Torq will sell it direct to you. It is pricey, but since I've changed my Simplicity over to the 5w30, I have noticed quite a difference in the low noise, and better power than I used to have.

Too quick on the typing. Tuff Torq is now recommending 5w50 synthetic oil, not 5w30. Sorry for the boo-haha.