Woods 121 Twin Cadet get out of time

[Troop4Christ]

I have an old 10' 121 Twin Cadet and I've got a few questions.

1. Where can I find the serial number on it? I've look everywhere and I don't see one anywhere.
2. While using it, every once in a while, I can hear the blades get out of time and start banging together. I have to stop the tractor and PTO, climb down, remove a pin on one of the secondary shafts, rotate the shaft 90 degrees, and put the pin back in, and then I'm good to go again.

Well.. I know the previous own had one of the gearshafts replaced a long while ago because he let one run dry and cracked the housing. AFAICT, the stamps on the housings of both the original gearbox and the new one are the same, 32420:

But it seems like to me, that one blade might be spinning slightly faster than the other one, causing them to eventual come in line w/ one another, resulting in the blades smacking into each other? I don't see any other evidence of any kind of gearbox damage, or slipping between the two. Spinning one blade underneath the deck, spins the other and both spin the PTO shaft. So seems like all of that's working as expected.

My question really is... Is it possible for a newer gearbox to be a slightly different ratio, enough so that after a few hours of mowing, it can get things out of time enough to cause this kind of problem, even w/ the housing stamps being the same?

3. Am I even on the right track here? or is there some other way these blades can be getting out of time in this way?

Thanks all!

 

[Janicholson]

I have an old 10' 121 Twin Cadet and I've got a few questions.

1. Where can I find the serial number on it? I've look everywhere and I don't see one anywhere.
2. While using it, every once in a while, I can hear the blades get out of time and start banging together. I have to stop the tractor and PTO, climb down, remove a pin on one of the secondary shafts, rotate the shaft 90 degrees, and put the pin back in, and then I'm good to go again.

Well.. I know the previous own had one of the gearshafts replaced a long while ago because he let one run dry and cracked the housing. AFAICT, the stamps on the housings of both the original gearbox and the new one are the same, 32420:

View attachment 68328View attachment 68329

But it seems like to me, that one blade might be spinning slightly faster than the other one, causing them to eventual come in line w/ one another, resulting in the blades smacking into each other? I don't see any other evidence of any kind of gearbox damage, or slipping between the two. Spinning one blade underneath the deck, spins the other and both spin the PTO shaft. So seems like all of that's working as expected.

My question really is... Is it possible for a newer gearbox to be a slightly different ratio, enough so that after a few hours of mowing, it can get things out of time enough to cause this kind of problem, even w/ the housing stamps being the same?

3. Am I even on the right track here? or is there some other way these blades can be getting out of time in this way?

Thanks all!

In my opinion the issue is slippage. either a hub and drive below the deck has sheared a key, or the drive shafts from the central box to one side is sheared. Put a dam of fingernail polish on the connections after wire brushing them and solvent to dry. if the nail polish is fractured, the key is sheared. Jim

 

[Troop4Christ]

But if they were sheared, wouldn't only just 1 rotor turn w/ power from the PTO?

 

[Janicholson]

But if they were sheared, wouldn't only just 1 rotor turn w/ power from the PTO?

The sheared key might have distorted the shaft to hub fit enough to drive the blade enough to do what it is doing. I can tell you that you are not going to find a difference in ratios. The small number of teeth on those bevel gears would have it tangled up in 10 rotations or less if the ratio was different. Find the slippage as I indicated. Or you could take everything apart and find it as the last thing disassembled. (nah too much work) Jim

 

[Troop4Christ]

Roger that.. Thanks Jim...

 

[mtf]

We run one of those mowers for years. It has solid square shaft between the gear boxes and a sleeve over the shaft where it slides in the gear box. That sleeve can wear a lot and cause lots of play between the gearboxes. That square shaft can twist slightly and cause blade tips to hit.

Our mower started slipping a cog on one of the gears in the gearbox. I think this is your problem as well. There is not a key to shear on output shaft below mower. It is a splined hub, that could be stripped if nut was loose, but you would have serious vibrations going on.

 

[Troop4Christ]

Yeah.. no vibrations.. guess I just need to get up under it, take it apart and figure it what's going on

 

[Troop4Christ]

Oddly enough.. the diagram on Messick's says it has two shear keys?

 

[mtf]

Well I was wrong, there is a key in the output shaft. That is a job to get the blade assembly off. Good luck.

Just curious, how much play do you have in the drive line between the gear boxes. That is with PTO disconnected from tractor. Try turning one set of blades back and forth. How much can you turn one side before the other side starts turning?

 

[Troop4Christ]

Quite a bit actually.. like, more than a 1/4 of a turn

 

[mtf]

With the help of someone else slowly turning one blade set back and forth, try and isolate where the most of that play is. It will either be in the shifting between the gearbox or the gearboxes themselves.

Do the gearboxes hold oil?

 

[Troop4Christ]

With the help of someone else slowly turning one blade set back and forth, try and isolate where the most of that play is. It will either be in the shifting between the gearbox or the gearboxes themselves.

Do the gearboxes hold oil?

Gearboxes seem to not loose any oil (the hydraulic lift cylinder is another story altogether lol), rarely have to add anything to them.

Gonna climb under there and see where the play is...

 

[Troop4Christ]

Well... Figured out why there's so much play in the rotation of these blades...

Pretty sure this hole is supposed to be actually square ... Oh boy

 

[Troop4Christ]

So my boy and I swapped the secondary shafts..

I'm thinking that the shaft that was in that disformed hole when I looked at it had been worn down.. So the reason it was getting out of time is that every once in awhile it would jump a quarter of a turn in the hole.

So we swapped the other one that isn't quite as deformed..

It does seem to be a little bit tighter.. still obviously not perfect. Hopefully it'll give us another season or so...

I gave it a test run by clearing some brush along my tree line with some thick stuff.. and it definitely seemed to do better.

So next time I bush hog we will see how it goes