Posted by Art Aytay on 10/25/2001:

Changing Hytran in a Hydrostatic Transmission


First get a gasket for the rear cover from a Cub dealer.  Don't waste your time using RTV to try to hold in 2+ gallons of hydraulic fluid. (I won't go into which brand of fluid to use...we've kind of been there, done that!)

Begin by cleaning the rear cover area of your transmission and filter of any grass/dirt. (drass?)

Put a pan under the filter and remove it.

Move the drain pan under the rear cover area of the tractor. Take out the FILL-PLUG with a 3/8" socket extension. Loosen all of the bolts on the rear cover but do not remove them all. Remove just the bottom three. With that done, begin trying to loosen the rear cover from it's cement-like grip on the rear of the tractor. You may have to remove more bolts at this point, but watch out, because when it opens up, you're gonna get a FLOOD of Hy-tran, so have a large (2+ gallon!) pan under it! You can use a rubber mallet with a block of wood on the edge of the cover, or if you're really lucky and careful, you can pry it off with something flat, but I can't over exaggerate the word CAREFUL in this case! Once the fluid is drained, remove the rear cover and clean it up.

Carefully scrape all of the gasket material off of the rear cover and rear of the tractor. (If you're a neat freak, you can use a green 3M pad to really clean up both mating surfaces.  Buff it till they shine!) Now is a good time to use a straight edge on the inside of the cover to see if the cover has any warpage at the bolt holes.  If it does, use a BFH and a thick piece of scrap steel or an anvil to level things up.
If your Hy-tran fluid is old enough, you may notice some gelatin-like, pinkish clumps left in the bottom after the fluid drains out.  That's what happens when moisture combines with Hy-tran.   Hy-tran, like automotive brake fluid, is hydroscopic; meaning that is absorbs moisture over time.  So get all the dingleberrys out of there!

This is when you marvel at the stout construction of that Cub rear end. Look for anything that's out of place or broken (Highly unlikely!!)

Clean out the bolt holes and bolt threads with your favorite spray cleaner (Brake, engine or carb cleaner works great.) before you re-install the bolts. If you've got a tap of the appropriate size, that will work wonders for cleaning out those threads!  Put the gasket and rear cover back on. You may use a little Permatex (gasket cement) but I don't simply because they don't leak when you use the dry gasket, and it's easier to clean up the next time you do it.  Put a dab of Hy-tran on the filter gasket so it doesn't bind and put the new filter on. Fill through "plug-hole" on rear cover until fluid runs out.
Put the plug in and start up the tractor. Drive it around the yard. Rev up the engine. Be amazed at how much better your cub drives and notice that the engine even seems to purr better. (That's a sign that the Cub-gawds are happy!) If you've taken your mower deck off, take it out side and pop a few wheelies, then bring it back in the warm, safe garage and check the fluid level. It will need about another quart from what went into that new MTD (made by somebody else!) filter, so top it off and replace the drain plug. If you've taken off the mower deck, now's a good time to change the oil and grease up all those zerk fittings. (Don't forget the one on the axle pivot!)

Editor's note: If you own a quietline tractor, now's the time to also take off the left (that's "Port" in the boat business) side engine cover and check the wing-nut on the aircleaner to make sure it hasn't loosened and then replace the damn thing with a ny-lock one!

Take it outside, pop about 10 more wheelies. (If you can get the tires to chirp, your neighbors will be watching you at this point!) and then park it in the warm garage.
The entire process is essentially the same for gear drives, minus the filter of course.

Some additional notes on Hy-Tran and filters by Steve "Mr. Plow" Blunier:

Hy Tran contains aditives that absorb and suspend water as well as additives that resist foaming.

The resistance to foaming is probably the biggest reason to use Hy-tran in a hydro. Hydros will not work if the oil has foamed or is being foamed by cavitation at the pump/motor...the froth generated by cavitated/foamed oil can cause damage to the precision machined plates within the hydro and hurt overall hydro transmission performance on hard pulling drawbar loads and or extremely hot days (mowing for several hours on a hot day).

The water suspension properties allow Hy-Tran to hold water in suspension within the fluid where it is safer than in a big pool at the bottom of the tranny (free to be sucked into the hydro in big gulps). Trannys will stay cleaner and more sludge free. This is especialy usefull for gear drive trannys and creepers, where the service intervals are much longer than the hydro units.

Hy-Tran is MUCH cheaper (than MTD branded fluid) at CIH farm equipment dealers. You can buy it in containers ranging from quarts to 55 gallon drums, price going down as the gallons go up. Personally, I just buy a 5 gallon pail and use it for several years worth of Cub servicing)

Oil Filters:

The Sundstrand hydro in our Cub Cadets uses a HYDRAULIC suction line filter, without any kind of "anti-drain back" valving. DO NOT SUBSTITUTE A CAR OIL FILTER. Automotive filters are designed for pressurized filtration and will not work correctly on your hydro. The anti-drain back valve in a car filter keeps oil in the engine oil galleys for faster start-up lubrication.......this valve can interfere with the charge pump's ability to draw oil into the hydro.

Use a Cub Cadet filter, or the correctly cross referenced hydraulic filter like the Fleet Guard HF6096


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