Old Snapper YT12D transmission problem [Archive] - LawnSite.com™

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kogafortwo

08-28-2009, 07:53 PM

My neighbor gave me an old YT12D Snapper riding mower for free to get it off his lot. The deck is good, the chassis is OK, and the twin cylinder B&S runs, so I would like to try and resurrect this old machine. The problem is with the transmission.

BTW, this is not a RER "Forest Gump" mower. It does have the disk/driven disk drive, but then the driven disk goes into the chaincase, chaincase output shaft goes into transmission/differential unit on the left side, then through a couple of intermediate shafts with a mix of chain drives (two) and a dual-range gear slector.

I some diagnosis. Here is the deal:

1. The chaincase works. The problem is NOT in the chaincase.

2. Spinning the rear wheels in high or low range makes the transmission shaft with the brake band on it spin.

3. The shaft with the brake band on it SHOULD be turning the shaft to the chaincase, but it doesn't. So I have isolated it that far.

I pushed the tractor back out to the woodpile and strung a tarp over it. Tranny work will have to be a winter project.

I am looking for someone who knows these trannys inside and can give me an idea of what to do next. The gang on Mytractorforum have taken a look but did not have an idea of what to tell me, and Snapper has not written me back yet.

Anybody who knows the old LT12/LT16/YT12/YT16 "D" series transmissions please help.

Restrorob

08-28-2009, 09:11 PM

Spinning the rear wheels in high or low range makes the transmission shaft with the brake band on it spin.

We use to be a Snapper dealer and I've been inside quite a few of these units....

If the above statement is true then both chains in the transmission is intact along with the one chain in the primary chain case.

The only thing that would cause no drive from the primary chain case to the transmission would be worn/stripped chain sprocket(s) in the primary chain case, This could let the transmission drive the primary chain case when turning the wheels by hand but keep the primary chain case from driving the transmission when under a load.

Remove the rubber drive disc from the primary chain case, With the wheels on the ground blocked and transmission in low range try turning the drive disc hub by hand. Or you could put a socket wrench on the nut holding the hub on, If the sprocket(s) are worn you will feel the chain jumping across them.

If you find no jumping/slippage, Look at the friction band inside the drive disc and the amount of pressure the drive disc applies to the driven disc.

mowerknower

08-28-2009, 10:11 PM

Not a snapper dealer and dont really work on too many, (and Ive had a few brews) but could the pin in the axle hup be sheered? Just make sure you check the obvious first

Restrorob

08-28-2009, 10:51 PM

could the pin in the axle hup be sheered?

If the tapered 1/4" screw in the either axle hub were sheered he wouldn't have been able to spin the transmission shafts, It would have shown up right then....

kogafortwo

08-30-2009, 10:31 AM

Mowerknower, yes I did check the shear bolts that hold the hubs on, thanks for the suggestion.

Restrorob,
the worn sprockets / stretched chain theory is kinda where I am going with this. Especially since the previous owner said he tore into it once, could not find anything wrong, so he put it back together the way he found it and parked it in his side yard (which is where got it from).

If he saw a broken chain, he would have taken care of that.

Oh, one more thing I forgot to mention:

When I did get the engine running, I put it in gear, let out the cluitch, and it went about 10 feet before it stopped in its tracks. So this gives me even more of an idea that the friction drive is slipping or the chain is jumping teeth.

This is my winter project for this year (last year's was the chipper). I will post a repair thread when I get it going, maybe some pictures and tips for people running into the same problem. Look for it in December or January - got 2 weeks off for the holidays this year.