PTO moves at high rpm when disengaged

[gcmiller]

Hi everyone. First time poster. I have a B2910 (about 470 hrs) with a front-end loader and a Caroni 91” finish mower. I bought these used, as a set, almost a year and a half ago and it’s my first tractor. This past weekend I was moving a pile of dirt with the front-end loader while the mower was still attached, but raised and the PTO was disengaged. I noticed the PTO shaft was spinning very slowly (roughly 60 rpm) when the engine was running above 2,000 rpm. Is this normal or something I should be concerned about?

I’ve tried searching previous posts first and I found several regarding the PTO spinning when the engine is at idle speed, but not at high rpm. Usually I’m either mowing or the mower is not attached, so I can’t be sure how long this has been going on. This was the first time I noticed it.

I never engage or disengage the PTO or shift the transmission unless at idle speed. The transmission fluid level is good. I know the mower is larger than recommended, but previous owner used this setup since new - not that that makes it OK.

Thanks in advance,
Gary

 

[85Hokie]

SO the mower is spinning (pto shaft to the mower) at that speed?
Is this a mechanical PTO? Lever type?- if so, is it possible that it is not all the way disengaged?

 

[07wingnut]

When you notice it spinning, try using a piece of wood to slow it down, but be careful for your personal safety. If it slows down with very little resistance from the wood applying friction to the pto, then it is probably a very weak coupling from the oil viscosity. This is not that abnormal. If not, there are probably more serious problems.

 

[Rosher18]

My tractor does this too. I don't own any PTO implements but I can watch the shaft spin slowly when the motor is at high RPM. I can stop the rotation with a finger. More than likely it's just oil viscosity coupling.

Sent from my VS986 using Tapatalk

 

[gcmiller]

SO the mower is spinning (pto shaft to the mower) at that speed?
Is this a mechanical PTO? Lever type?- if so, is it possible that it is not all the way disengaged?

Thanks for the replies everyone.

Yes, the PTO shaft is connected to the mower and it is spinning all 5 blades of the deck very slowly.

The PTO engagement is a lever. I've tried multiple times to make sure it was completely disengaged, but it's the same thing every time.

When you notice it spinning, try using a piece of wood to slow it down, but be careful for your personal safety. If it slows down with very little resistance from the wood applying friction to the pto, then it is probably a very weak coupling from the oil viscosity. This is not that abnormal. If not, there are probably more serious problems.

I'll give this a shot, but it's already spinning against the pressure of the large mowing deck. It might be a day or two until I can.

 

[mbu]

I believe your tractor has a hydrostatic transmission and a Hydraulic independent PTO. Therefore, it has some form of PTO brake incorporated into its hydraulic independent PTO system. The function of the brake is to overcome the tendency of the PTO shaft to continue rotating, even when it is in the OFF position. This undesirable rotation is caused by oil drag between the drive and driven discs in the clutch pack.

 

[gcmiller]

I believe your tractor has a hydrostatic transmission and a Hydraulic independent PTO. Therefore, it has some form of PTO brake incorporated into its hydraulic independent PTO system. The function of the brake is to overcome the tendency of the PTO shaft to continue rotating, even when it is in the OFF position. This undesirable rotation is caused by oil drag between the drive and driven discs in the clutch pack.

You are definitely correct about the hydrostatic transmission and I'm sure you are right about the hydraulic PTO. Is the PTO brake something that can be adjusted or should I be concerned about it being damaged? I can't find anything about it in the owners manual and I have not purchased a shop manual yet (assuming they are available).

 

[kuboman]

It shouldn't turn with the drag of the mower attached. That is more than just oil drag. I believe your pto lever runs a valve which opens and closes the flow of oil to the pto clutch. I think you maybe have a leak in that valve which is letting oil to the clutch giving partial engagement. You might be able to adjust the valve or replace it. Are you sure it is a hydraulic clutch?

After looking at parts book it does not have hydraulic clutch. It has mechanical engagement with main drive clutch for engagement. So I am at a loss as to how it can turn at all except at engine speed. ??????

 

[mbu]

gcmiller,

If you don't have a parts list for your B2910HSD you can download it... Perhaps from this you can see if you have a valve like kuboman suggested.

Click on the following link and then scroll down until you find B2910HSD.pdf

http://kubotabooks.com/AutoIndex/in...s/&AutoIndex=27e3ea3205ff62b21bd11b6ca59b9fa8

 

[gcmiller]

mbu, thanks for the link. That is very helpful.

Kuboman, looks like you are correct and it does not have a hydraulic clutch. Now I'm really scratching my head.

 

[kuboman]

mbu, thanks for the link. That is very helpful.

Kuboman, looks like you are correct and it does not have a hydraulic clutch. Now I'm really scratching my head.

What happens when you step on main traction clutch?

 

[gcmiller]

What happens when you step on main traction clutch?

Well I never step on the clutch unless I'm at idle speed and the PTO is only spinning in the disengaged mode when the motor is above 2,000 rpm. That said, when I do want to use the motor the PTO does not spin when I step on the clutch and it starts to spin as I raise my foot.

 

[lugbolt]

91" mower? Did I read that correctly?

The PTO clutch also has a brake built into it. The brake is responsible for stopping the shaft from turning.

With a big mower, you have a lot inertia when turning off the mower. When you turn it off, the heavy weight of the blades will continue to turn the pto shaft from inertia. The brake plate in the pto clutch is "engaged" when you turn the pto to the "off" position. When disengaged at a higher speed, the brake plate is going to wear a little due to the inertia of all the blades....over time it's gonna wear out, and I suspect this is what's going on. Sometimes one can remove the hydraulic filter, cut it open and take a look-see what's inside. If you find a lot of clutch "mud", and that's exactly what it looks like (mud), prepare to disassemble the tractor and repair or replace the PTO clutch.

I've seen this often with the 70, 85, and 95 M series tractors but not too much with the B's.

 

[gcmiller]

Thanks lugbolt. You did read right, it's a 91" mower and it's big. The setup came with the house my wife and I bought along with an RTV900. The previous owner used it to mow a 5 acre pasture, which is what I now use it for. I believe the manual says the tractor is rated for about a 60" or 65" mower, so I'm well over that.

Based on the previous owners suggestion I engage the mower at idle speed and slowly increase the throttle until I get to 2400 rpm. When I'm done mowing I back off the the throttle slowly until I get to idle speed and then I disengage it. The previous owner suggested this to help avoid snapping the belts on the deck, but I would think it also helps with the inertia you mentioned. Still, it's a lot of inertia and you may be right that it's wearing the brake plate.

It would be tough spending money to get a smaller deck and take more time to mow, but that may be what I need to keep the tractor in good shape.

 

[kuboman]

There is no pto brake on the B's that I am aware of. Even so there is no oil drag that can make the pto rotate with this setup. Since there is not pto clutch there is no way to have rotational drag. I am stumped.

 

[lugbolt]

I need to back up....

Last tractor I had apart had hydraulic PTO....and I was thinking of that tractor and not a 2910. One I was thinking of was a M8540HDC.

There isn't a hydraulic clutch on the 2910. Mechanical. Thus, the only reason I can think that it might be turning at higher RPM is either one of the gears is tight on the shaft causing drag, which seems like it'd also turn at lower speed, or viscous friction causing it to spin a little. Dad's old Ford will do this but his uses 80w90 in the transmission and not Super UDT2 which is a LOT "lighter" viscosity-like 5w or something like that. I can't see it dragging much with super UDT2.

 

[gcmiller]

I finally found some time to get back on the tractor and I'm felling slightly stupid, but relieved at the same time. I recreated the situation and what I found is that the plastic casing around the PTO shaft is spinning from the vibration of the tractor and the actual shaft itself is not moving at all. I would have realized this from the start if I looked at the universal joints instead of the center of the shaft.

I hate that I got a bunch of you confused, but I sure do appreciate all the help.

Thanks,
Gary

 

[85Hokie]

I finally found some time to get back on the tractor and I'm felling slightly stupid, but relieved at the same time. I recreated the situation and what I found is that the plastic casing around the PTO shaft is spinning from the vibration of the tractor and the actual shaft itself is not moving at all. I would have realized this from the start if I looked at the universal joints instead of the center of the shaft.

I hate that I got a bunch of you confused, but I sure do appreciate all the help.

Thanks,
Gary

Well, lesson learned! Many a strange thing happens with these machines!

Dont feel bad - many years ago there was a post about a guys tractor that would not move forward in drive, after many discussions, came to find out the rims were spinning INSIDE the tires! And it has come up more than once!