You might have to do the clean up in steps or phases since you already have some "cake" on the surfaces. I will offer these suggestions. You will be able to clean it up better if you can/will remove the deck from the tractor first, so it may be turned up side down across two saw horses, or "leaned against" something solid (a nice shade tree is good). Also, having a pressure washer to "blast away" at the cake is better than plain hose pressure. I also suggest you take the blades off for your own safety and to make the deck surfaces more accessible (besides, they can probably do with a good sharpening). If you DO leave the blades on, cover the ends and edges with some "duct tape" to prevent your hands getting cut or scraped. It's not just the risk of needing sutures to close a serious cut, remember, these blades have been in contact with grass, dirt, and the "poop" of birds, dogs, and untold other fauna that may have trotted through, or flown over, your yard. The risk of infection from even a slight cut is realistic! Anyhow, back to cleaning. The first thing you want to do is remove as much of the "cake" as possible. Pressure washer is about the best tool for this. Try not to direct the spray into the spindle seals (where spindle shaft disappears into the spindle body). When cleaning near the spindles, always make sure the stream is blowing AWAY FROM the spindle shaft and not toward it. If you don't have a pressure washer, you will have to "scrape" with something. I DO NOT recommend metal scrapers for this because they will gouge the paint (but you are probably going to find a bunch of scratches and gouges anyhow). If you are going to "manually" clean the stuff off, you need to wet the stuff thoroughly with a garden hose first. Let that sit a while (with repeated soakings) until it begins to "soften". Use a nozzle on the hose that "focuses" the stream into a small, high pressure "point". Any sections of cake that loosen, try to get the water stream behind them to encourage them to shed. Any cake that does not "turn loose" will have to be scraped with a plastic or wooden stick (paint paddle type of stick). After you have scraped away as much cake as you can, mix up a "strong" solution of laundry detergent in a pail. Using a STIFF bristle brush (plastic bristles), get in there and scrub vigorously. Rinse often and re-scrub stubborn areas until you get all (or most) of the organic film off. Once you get it as clean as you can (or just give up), let the deck dry completely. Directing a "window fan" or "squirrel cage blower" on it will speed this up. Placing it in the bright sun with a fan is even better. After it is dry, you need to "touch up" gouges and scratches, or you can go wild and paint the entire thing. Before applying any paint or primer, wipe the area well using a clean cloth moistened with a "no sanding" surface prep such as "Sand ban" or similar product. Bare metal needs primer before applying paint. After your "touch up" painting, allow the paint to "cure" (at least 3 days) before treating with your "silicone based product". Be advised.....you may have to make this an "annual" procedure. At least you will be able to add years to the life of your deck (barring encounters with immovable objects).

Thanks mownie, didnt even think of a pressure washer

I think renting one is worth ending the pain of elbow grease :)

Or you could build one to run off the PTO of your tractor ;)

I do as mowie suggested pressure wash, then soak with engine degreaser and pressure wash again. I try not to spray directly on the spindles though. And if there is a really hard caked on spot the the pressure washer won't blast off I hit it with carb cleaner or brake cleaner.

I read somewhere that it was not advisable to get the underside of the deck wet as it could promote corrosion. I may be wrong but you should check it out first.

***"I read somewhere that it was not advisable to get the underside of the deck wet as it could promote corrosion. I may be wrong but you should check it out first."***
I'm not sure what the intent of the poster might be in posting that remark. I thought the thread was about getting rid of cake build up that would hold moisture that would promote corrosion even worse than getting the deck wet in order to clean the cake build up from it to apply a product that will help minimize cake build up which promotes corrosion. Huh? Or......you can't make an omelet without breaking some eggs. But the only real way to keep from getting the underside of the deck "wet" is to never mow live grass with it. Mowing live grass will expose the underside of the deck to moisture from the grass clippings.

I think the poster was talking about not getting the spindles wet, which is advisable. I have had very good luck using a 1 1/2" putty knife to clean my deck. I am not worried about scratching the pretty paint on the bottom of my deck though. I guess that happens when you have a 15 year old mower ; )

I read about people using wd40? I've tried PAM and it seemed to work alright. Found some useful info at the link provided too...

Here is a link that might be useful: grass build up on deck

Metal : Fine Grade Toilet Paper and Gel Toothpaste will Provide a Better Job !

Schmitty: Bio-Degradable Engine Degreaser and Pressure Washing washing as Mownie has advised will remove most if not all the caked on Grass. Any left over can be removed with a wire brush . Once cleaned apply a light coating of grease to the exposed spindles to reduce potential for rusting . Routine cleaning after cutting with garden hose and air drying is required. All decks (Steel) will eventually rust .

Hey MOWNIE, The other day my brother told me he saw a guy with a tractor in the ditch with the deck fully submerged in water , running the mower,that cant be good . Hope he has greasable bearings LOL.....

I have a Craftsman Lawn Tractor 917.28736 purchased in 2007. The Operator's Manual gives no instructions on cleaning the underside of the mower housing. However, there was a "Troubleshooting Guide" addition which states, "Important: Do not wash mower with water from a garden hose or pressure washer. Water in the blade mandrel bearings will shorten the useful life of the mower and could result in a service call." Thus I presume any cleaning would have to take this into consideration. On p. 20 of the Operator's Manual they do cite keeping water out of the engine and transmission, and then further advise: "Use compressed air or a leaf blower to remove grass, leaves, and trash from tractor and mower."

I agree with most everything stated. Very good advice. I've had under deck problems for most of my mowing life. And have lost most of the battles even after washing, scrapping, and blowing decks clean. For the top of the deck, only mowing when the grass is is dry, and blowing the top clean after each use is the best thing to do. Even washing the top off and blowing it dry works. But grass build up under the deck is a problem. I've washed. I've scrapped. But I've always had problems with surface rust pitting the metal. Then the buildup gets worse as the years go along. Last year I started using Fluid Film. I have no more grass build up. I have no more surface rust. The little dirt build up I get comes off easily. Just spray another coat after a mow or 2, and keep on going. The stuff works.

The top part of the deck should be waxed 2 or 3 x a year. then a leaf blower works easier .I had a 16 year old JOHN DEERE I sold last year and it was like new other than a few scrapes. I used to wash my mower every 3rd or 4th time and replaced bearings in mower at 12 years average 60 hrs a year .My new mower has only been washed 2 geting away from this washing all the time . As far as the bottom I use car ramps to scrape mine if it is too heavy the deck comes off , you will shorten the life of a deck by not doing this task. The worst thing is storing a mower in the winter months with this gook on it , maybee it is time for TEFLON bottom decks?

I agree with you 100% doberman.
7 years ago my neighbor and I both bought new tractors about a week apart.
He brought his over to show me and the first thing I said was "don't wash your tractor".
I even offered to let him use my air compressor any time he wanted.
Well after the first mow I see him in his front yard washing his tractor.
Last year he came over crying about the $425.00 bill he got from the JD dealer for new deck spindles, blades and belts and this was after just about 100 hrs.
My tractor only gets a "real" bath just once a year right before winter storage and thats with the deck off.
All the other cleanings involve compressed air and a damp rag.

Interesting- I owned a JD 316 with a 46" deck that I never washed and rarely cleaned in the 25+/- years I owned it (bought used) and the deck was "rock solid" when I traded it in (engine needed rings) for a new X500. Are these new decks so "cheezy" they need that much attention to cleaning?

I guess it all depends how much time you want to devote to this task .The decks are well built on the 500 series it is as heavy duty as my old 38 and that was well built.What size deck did you get,and how do you like your 500?

Don't know , perhaps the Canadian Grass is self lubricating ! Have had almost half dozen lawn mowers in my time and have not had a lot of trouble with under deck rusting . Oh perhaps light discolouration and paint peeling , but not enough to reduce the discharge or mulching of grass . I have always routinely washed the grass out from the underside immediately and air dryed on cement pad along side of the garage . I agree if you leave accumulation under deck over the Fall / Winter you will have serious rusting issues .

doberman - I purchased the 48" deck for my X500. So far I like it fine, however it only has been run 6 hours.

I once had a push mower with a magnesium deck that was rust proof, even though there was some grass buildup. Cleaning was very easy and no worry about painting or treating the deck undersurface. Why don't manufacturers make magnesium decks for lawn tractors?

would suspect cost. Takes a die casting and multiple shots just to get the first good casting. Magnesium is also something of a safety hazard, being fire-prone.
Low relative weight, high strength, corrosion resistance are good, tho...

Grass has water in it

I clean my mower each time I use it

Right on Wendy and Canadian grass has even more moisture content apparently due to the heavy ambient snowfalls !