1250 Bad shaking when front PTO engaged
 

Hello,

New member and first post. I have a recently acquired 1250 that had been a project for the two previous owners. The person I bought it from did a lot of mechanical work and it appears to be in pretty good shape. My parents had a Cub Cadet when I was growing up, can't remember the model but they got it new in the late 60's. So I'm familiar with them in general, it's just been 35-40 years since I've used one with any regularity.

The only problem that I'm having is that about 9/10 times when I engage the PTO for the mowing deck, the tractor will start shaking/vibrating so bad it will almost stall out. If I immediately disengage the PTO it will continue to shake until I drop the motor speed to idle and then it smooths out. On the rare occasion where the shaking does not occur initially, usually after a few seconds of mowing the shaking will start. There have been instances where it has literally stalled out and will start shaking immediately if I try to start it again.

Just riding around without the PTO engaged it is smooth as silk (well as smooth as expected), no issues whatsoever. Starts right up, idles fine, no weird vibrations, all OK.

After doing some reading here I've done the following: Checked and reset the air gap, it was way too loose/big. Removed the drive belt and checked the bearings and pulleys on the deck, everything rotated easily, per the previous owner he had recently installed new bearings and lubed it. All looked and seemed normal. Reinstalled drive belt, as soon as I started and engaged the PTO same shaking/vibration occurred again.

Took the drive belt off, started it and engaged the PTO, nothing strange happened. Just like running with the PTO disengaged.

Kind of wondering where to go from here. I almost wonder if the bearings in the PTO are bad? It would seem it only happens when the PTO is engaged and under load. Almost all of the time I'm at a dead stop in neutral so I think that rules out any driveshaft or transmission related issues. Any thoughts or suggestions would be welcomed.

Thanks!

I should probably mention that the last owner converted this to a solid mount engine with a beefed up cradle, IIRC he either got the idea here or got parts from someone here but I may be wrong on that. Also has a new flex coupler on the motor side of the drive shaft and the transmission side joint is a U-joint.

Have you checked the blades on the deck? Might have one bent or missing a piece that causing them to be unbalanced.

You know, I didn't. I just checked to see if they were spinning freely. When I purchased the tractor I did drive it for about 10 minutes with the deck engaged, appeared to work just fine then and on one instance when I cut for about 10 minutes once I got it home. Have not hit anything with them. I'll have to take a look.

These are noisy and vibrate enough as it is, but it seems like it's coming from up front as opposed to underneath?

If you really believe it's the PTO I suggest removing the grille and starting the tractor and engaging the PTO, look to see if the PTO pulley is running true or is it running out of round. This will help narrow down where the issue is. I shouldn't have to tell you but I will anyway, KEEP YOUR FINGERS AWAY FROM THE PTO.

With the drive belt on or off? With it on I have to immediately shut it down, I don't think I could get around there quick enough to see it before it stalled, might have to get a helper.

I would do it with the belt on since that's when you really have the issue.

Can't see the PTO through the grill on a Quietline. Air box is in the way.

The air box completely covers the PTO? My 1211 is setup just about the same as a QL and I can see the PTO on it.

The muffler box pretty much hides the PTO clutch. Remove the side panels to observe the PTO clutch.

Kinda what I thought from my dive in there the other day to set the gap.

That's stupid, I guess I can add that to my list of reasons not to own a QL.

You check them mule drive pulleys?

Tim, quit whining about Quietlines! They are great tractors and will run on a hillside without throwing a rod...usually! You need to try out a few and realize they are not the "Edsels" of the Cub Cadets :biggrin2::beer2:

Tight in there.

Yes, checked the mule drive pulleys while I had the drive belt off.

I mentioned at the end of my initial post, this has been converted to solid mounts and a beefed up cradle.

It's not a light vibration by any means, this is a hood shaking I'm gonna tear myself apart shaking. And most of the time as soon as I disengage the PTO and drop it to idle it completely goes away.

Have you taken off the deck and removed the belt cover to inspect the belt, pulleys and spindles? :bigthink:

Smart move would be to drop deck and check/balance those blades, unbalanced blades can ruin bearings real quick. Somewhere in that driveline you may have a bad bearing but it sounds more like a broken or unbalanced blade.

Other than freewheeling the deck while I had the tractor up on ramps I have not done a further inspection. What's got me stumped is that it has worked just fine a few times but certainly not with any consistency.

As I mentioned, this was a project coming to me. Two owners ago it had some cosmetic work done, wrong color yellow, I know.

I know the deck is not from this model either, perhaps these pics would help ID it?

Yes you have a 48" deck with a 44-50 style mule and hanger. The angle of the brackets for the front pulleys on the mule have a different angle than what that old style 48" deck uses. Double check the pulley and belt alignment. Also check the pulleys on the deck and spindles to verify they are running true.

As others has said...check the blades for damage!

Given what I highlighted, and the fact you say it has been converted to solid mounts, I think that the engine is loose on the cradle. If the shaking continues after you shut off the PTO, and continues until you slow the engine, I am betting your engine is loose.

So, the best asked question here would be, have you watched this problem with the hood open or the side panels off? That would be the first, next best step. A broken, unbalanced blade, or a bad bearing..... or really ANYTHING deck related would not continue to happen, and keep happening until you slow the engine, and definitely wouldn't shake bad enough to stall the motor. Pull the side panels, and maybe even the hood and watch what's going on. Set a weight on the seat (if it still has a safety switch) STAND AWAY FROM THE DECK and engage it while standing next to it. Lower the deck before hand and make sure you don't get near it. Can't stress safety enough here. Check it out, look it over.... you have got to be able to see a problem that big.



Just as a note, the u-joint on the rear shouldn't be an issue..... but it isn't OEM. Might pull the tunnel cover and while it is NOT running, check to see that the u-joint is tight. DO NOT run it while sitting in the seat with the tunnel cover off. Just not safe. Key body parts are just too close to bad things if there is a problem when your sitting in the seat. :bigeyes:
But, with solid mounts, the u-joint should work. As much flex as the the system was designed for, that u-joint may have worked loose. Don't know how the attached it to each shaft....



I have never in my life balanced blades. NEVER. I have mowed acres and acres and acres and never had a bearing failure. Not even for them being worn out. Not yet anyway. While balancing the blades makes sense, I can't see that they could ever be so far out of balance that it would cause an issue, unless they have been broken and a large piece is missing. Besides, the tip speed on these old machines are so slow, I don't think you would ever notice the difference.

Pull the tunnel cover and checkout the driveshaft. I'm thinking the mower has nothing to do with it. The driveshaft is always spinning at engine speed and if it goes out of balance turning the pto off won't help but idling back the engine will. The shaft should go into the bearing at the rear coupler on the hydro pump. If it's short and not going into the bearing the only thing holding it centered is the rag joint. Who knows what one of the PO's did to the driveshaft. Good luck

Went back and re-read the original post- missed the part about a u-joint at the rear. A lot of u-joints aren't made for 3600 rpm. I think that may be where the problem is, or at least another place to look if you can't find anything wrong with the mower.

I can certainly try that and check it out. The only reason why I don't think it's the drive shaft is it has NEVER happened unless the PTO is engaged first (but maybe that's enough to throw it out of whack?). I driven it around for 15 or 20 minutes and it's smooth as can be until the PTO is engaged.

Will be at least tomorrow till I get a chance to mess with it. I'll certainly follow up on all the suggestions and report back.

PTO bolts loose on the front of the engine?
one or more adjusting springs broken or missing?
Loose engine mount bolts?
Loose or missing engine cradle mounts/bolts?
I agree w/Jon, some thing THIS BAD should not be hard to find ad should be fairly obvious upon closer inspection.

More things to check. When I adjusted the air gap all the springs were present.

I've got a copy of the owners manual, it really doesn't get in to much detail, I need to try and find a service manual. Can anyone point me to an online version? Or at least some parts diagrams? It's so hard to get in there around the PTO I'm not even sure how it mounts to the motor.

I've had the driveshaft cover off, I don't recall trying to engage the PTO at that point but while just running it was fine/smooth. I mentioned in an earlier post this seems to be coming from the front of the tractor, not the rear but who knows.

Did you read my post #20? Check the engine mounting.


Chassis manual can be found here:
http://www.onlycubcadets.net/forum/s...ead.php?t=4644

Yep, All that is on my list to check.

4 special bolts hold the brake flange to the block.
The springs you said you checked go over them and the bolts recieve 3/8" fine thread ny-lock nuts.
That is how the correct gap is adjusted. .010"
The service manual you need is GSS-1464 w/revision 2 Sept 1979
Pages 2-81A thru 2-81B

Those bolts just hold the coil to the block. If it was loose, engaged or not, it would not cause a vibration. PLUS, it would screech and squeal because the PTO rotor would be hitting it, causing all kinds of noise and heat. The PTO rotating assembly is held on with the center bolt through the crank.

I agree with engine mounts on this one.

The bolts hold the brake flange to the block.
And they are somewhat special in that the are coarse thread on one end and fine thread on the other plus the flange head in the center of the bolt
I stand corrected.

OK, had some time to mess with this today. Posted some pics at the end and if I'm smart enough I'll post some links later to some very short videos I took.

Just for grins, I started it, lowered the deck on the ground, engaged PTO, ran just fine for about 10 seconds. Disengaged PTO, reengaged PTO, ran fine again for about 10 seconds. Disengaged PTO, drove over to the yard, reengaged PTO, cut about 20' of grass and it started bucking so I stopped moving. Just let it sit there to see what would happen and after about 15 seconds it smoothed out, started to roll again and 5' later started bucking again. Decided to take it back to the garage and make some of the checks people had recommended.

In the order that suggestions were made:

Put it up on ramps, checked the blades. While they are incredibly dull there are no missing chunks, pieces etc. They all seem to spin freely with no binding.

Took the drive belt off, checked the mule drive pulleys. They spin freely, no binding and appear to be aligned fairly well.

Have not taken the deck off yet, but the belt appears to be in fine shape, pulleys all seem to be as they should. Certainly nothing binding or anything like that.

Checked all four of the bolts holding the cradle to the frame. None were loose. The person I bought it from had used Nylock nuts which was a good idea.

Pulled the driveshaft cover. U-joint seemed tightly affixed at both ends, no play.

Checked the flex coupler at the front of the driveshaft, it also seemed tight, no play.

All the PTO adjustment nuts/springs are present and I've got the air gap set correctly.

Started it with side covers off, hood open, drive shaft cover off. As expected smooth. Engaged PTO with deck down, ran it for about 10 seconds, smooth, disengaged PTO. Reengaged PTO, started to buck, let it run for a few seconds for the video, disengaged PTO, still bucking, dropped the engine speed to idle, quit bucking.

Thoughts on where to go from here?

Edit: Darn it, pics are all upside down. I've tried rotating pics , no luck. Sorry!

First video running, PTO not engaged

https://youtu.be/SvlgtaIdMGc

Second video PTO engaged, running normally, you can hear when I engage it.

https://youtu.be/VJ32TzsokH4

Third video, PTO engaged and bucking. Near the end I disengaged the PTO, it's still bucking until I drop the throttle.

https://youtu.be/y72DxgpXRHY

The PTO Clutch Assembly does NOT look like a Cub Cadet PTO. Not saying that is the problem, but it sure looks weird.

:bigthink:

No idea. On closer inspection it does appear there are some incorrectly sized flat washers where the adjusting studs are. There's a gap where I circled it.

It sounds to me like the engine don't have enough power to do the job,
like the carb is lean or the gov. is not kicking the butterfly open.:bigthink:

That coupler at the hydro pump end isn't factory. Should have a fiber/rubber disc like the front. Thought I would mention it, but looks like a nice part.

I agree.

Get the Kohler manual we linked you to earlier. Go through the governor set up. Readjust the governor control, make sure the springs are set in the proper holes. Then, check and adjust the timing, tune the carb, and if it needs it, tune up the engine. Sounds like for sure the governor needs adjusting, timing is off and likely it isn't getting enough fuel.


Oh.... next time you make some videos for us to help you diagnose, it really helps if they are longer. One was only 5 seconds. As a mechanic, believe me, that is barely enough time for my ears to even realize I'm listening to a running engine. In now way is it long enough to diagnose. Videos need to be a bare minimum of 1 min long.

Sorry about the shortness of the videos. With the upload bandwidth available in podunk Tennessee even the 5 second videos took almost 10 minutes to upload, each.

This may be an ignorant question but after looking at the deck manual and the tractor again I noticed it has no idler ratchet. While I don't think this is the problem, what's the implication of not having one?

The idler ratchet just lets you push the idler back and hold it there to release tension on the belt when removing or installing the deck. It won't affect the operation if it's not there.

You said the cradle bolts are all there and tight but are the bolts holding the engine to the cradle all there? Can't tell from your pics.