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Hi all. I have an old D125 that I bought new in 2007. The deck a big enough hole in it now that it was affecting the grass discharge. I bought a new deck and put it on, adjusted it best I can. I measured the blade height, it looks like it is 2" when the leaver in in the 2 slot. The problem I have is that when the mower is running and the blades turned off, then just raise the deck all the way up, the blades start up. What would cause this?

If it has a cable controlled PTO check that the cable is not catching on something when you raise the deck.
If it has the rod controlled PTO, same story get some one to sit on the mower and raise the deck while you watch t see what is tightening when you lift the deck.

Thanks for the reply. I'll check the cable and see if it is catching on something. ?

I looked and the cable is not hitting anything. I though that useing it for a bit might stretch the belt, but it still comes on when it gets raised up.

godsey1 said:

I looked and the cable is not hitting anything. I though that useing it for a bit might stretch the belt, but it still comes on when it gets raised up.

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I work at a Deere dealership. Did you buy a complete deck already assembled or did you buy a new shell and swap components? Can you attach any detailed pics of the deck lowered and raised? Maybe a visual will help us diagnose. Thanks!

I'll get pictures this evening. Thanks for your time. It is complete. Off Ebay.

When you lift the deck does it rise strait up or go backwards ?

I'm not sure. I will try to get pictures of it tomorrow and post. Just dont have time today. Thanks for the help.

It seems like it lifts straight up.

If the PTO is off in all of those photos you need a longer belt or a stronger release spring on the tension arm.
Are the pulleys all the same size as the old deck ?

From those photos that belt is way too tight if the PTO was off.
THe deck belt should be sitting against the belt keeper not deep in the pulley.

When it's in the down position it has plenty of slack, only when in the highest position does it get just tight enough the start the blades. And the blades were off in all the pictures. I may put the old belt on it just to see what it does.

On most decks the engine pulley & the deck pulleys are in alignment with the deck at the middle height position .
Thus as the deck is raised the belt goes slack then tight towards the top.
On the JD decks the belt should sit at the very outside edge of the engine pulley when the PTO is off.
In fact without the front belt keeper the belt should fall off the pulley when you turn the PTO off.
Then there is the position of the D hanger.
On some decks it points forward & on others it points back

I have never had cause to check this on a JD deck, but on most decks there is a variety of different blade pulley sizes.
The longer the blade the bigger the pulley in order to keep the blade tip speed within legal limits.
MTD for instance use the same engine pulleys and varied the blade pulleys on all of the manual PTO mowers.
On the electric PTO mowers they vary the size of the PTO pulley.
This I found out with a customer who was making a Fraken mower out of 3 partially deceased mowers.
IT cut great but the discharge chute would lift all by itself & it would throw rocks 100 yards.
Solution was to fit bigger pulleys on the blades to slow them down.

Thanks for the great information, I'll check that this evening when I get home. The only thing that I dont know the setting of is the rod that is in front of the deck. I dont know which hole the rod should go in.

That should be in the owners manual which is a free read ( you can print out small sections only ) off their web site.
Generally the right hole will show substantial wear

bertsmobile1 said:

That should be in the owners manual which is a free read ( you can print out small sections only ) off their web site.
Generally the right hole will show substantial wear

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To add to bertsmobile1's advice,
The factory uses the top hole for the front deck link. Do you know what model your 'new' deck came off of? If you do, I can look and see if the part numbers are different in Deere's system. The factory put a serial number sticker by one of the rear deck mounts. It may or may not still be there.

Your belt should be part number GX20072. Pretty much that whole series over the years used that belt number. Also make sure you have the 'ball' between the locknut and bracket for the front link. See the parts diagram attached. (In your first pic, the ball looks like it is below the bracket, which is a common mistake we see here in the shop)

You will need to adjust your front-to-back level to get the link set right. Assuming your tires already have the correct amount of pressure in them (12-14psi in front, 10-12psi in rear). On a level surface, rotate the right side blade so it is pointing front to back. With a deck leveling tool or a short ruler, measure from the floor to the tip of the blade. Adjust the front link so the front tip of the blade is between 1/8-3/8 inch LOWER than the rear tip. This ensures that only the front tip is doing the work as the blade spins. If this adjustment is perfectly level or the rear tip is lower than the front, the engine has to work twice as hard as both ends of the blade are cutting at the same time. This will also overload your mowerdeck and shorten the life of the deck belt. With the blade properly pitched, the front tip does the cutting while the rear tip only has to propel the grass around and out of the discharge opening.

Note: If you run out of threads on the link, you must bend the black bracket forward a bit and retry the adjustment. That bracket relaxes over time or if you hit something with the deck, it can get bent back a bit. Just remove the link and bend it a little forward with a large adjustable wrench or any tool you can get a firm grip on it.

Isn't that deck used on the 2 small residential ZTR's as well ?
Fairly sure I put a deck off a 120 that I welded up on a 225 (?) while I was welding his deck back up.

bertsmobile1 said:

Isn't that deck used on the 2 small residential ZTR's as well ?
Fairly sure I put a deck off a 120 that I welded up on a 225 (?) while I was welding his deck back up.

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I researched the part number and it only lists the tractors. I haven't converted a tractor deck to a zero turn deck, but the deck shells are similar. Biggest difference is the zero turn has electric pto and rear engine versus manual pto and engine in front on the tractors. I imagine with some welding and changing of pulleys, it can be done.

Here is the description from the auction: John Deere 42 inch Complete Replacement Deck Fits L100 Series D100 Series LA100 Series AUC13429.

godsey1 said:

Here is the description from the auction: John Deere 42 inch Complete Replacement Deck Fits L100 Series D100 Series LA100 Series AUC13429.

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The original L100 series decks had sliding rear adjusters and two-bolt blade spindles. Deere then changed the adjusters to a threaded adjuster with locknut and center bolt blade spindles, which is what you have. So it looks to me that the deck is correct for your machine. Make sure they didnt install a generic belt. Make sure the part number of the belt is GX20072. Deere stamps the number on the belt. If it is generic, put a Deere belt on it and see if that makes a difference. Deere engineers their belts for the specific purpose in which they serve. Whereas generic belts are manufactured for general purpose. The length and width may not be correct for this application. We have had this issue here at the shop, so it wouldnt suprise me if that is what may be happening here.

I'll look when I get home. Thanks again.

I hooked the rod on the front into the top hole in the bracket on the deck and it seems to have helped. The blades dont start up now. It looks like the deck itself was pushing the belt up as it was raised.