JD F935 - PTO won't engage

[CentralNC]

I recently bought a JD F935 front deck mower with about 1500 hrs on it. I have used it about 10 hours total and just had a problem with the mower PTO.

I was cutting the grass around some pine trees when a neighbor drove up on a 4-wheeler. It sort of scared me and I hit the brake on the mower without reducing the rpms. Hitting the brake immediately stops the pto/front deck mower. I lower the rpms and had a conversation with the neighbor.

I tried starting the pto again and it would just "click" beneath the seat but not engage. I thought it might be the seat safety switch or the brake safety switch, but I don't think those are the problem. If the parking brake is engaged the switch won't make that "clicking" noise underneath the seat.

I checked the fuses and then all of the plugs I could find. I was able to get the mowing deck to engage last night before I put the mower away for the night. I thought it was just a loose switch. I tried it again today and couldn't get the pto to engage at all. I just get that clicking sound.

There are several possibilities, but I am not sure how to narrow them down. I really don't want to haul it to the dealership either. Does anyone have any thoughts or suggestions?

Thanks.

 

[zzvyb6]

Did the belts come off the pto shaft at the rear engine pulley?

Does the mower deck engage but the lever won't stay in the fwd position?

Manual suggests checking the PTO switch for proper closure. This implies that the contact plate may need to be adjusted to ensure that the switch closes.

Check the PTO clutch itself by separating the connector at the flywheel. Jumper the black wire to ground. Jumper +12v from battery to the blue wire and listen for a click. (That's good).

Other tests imply that the connectors under the RHS fender panel need to be checked. A heavy braking lurch could have loosened one of them up.

Jumper the seat switch to see if that's the problem. It also may need adjustment or clearance, for example if dirt or a beer can slipped under the seat and is blocking the contact

I've had some issues with mine as far as the micro switches lining up with their contact plates. As I recall there's also one near the PTO brake band that gave me some trouble.

Of course you need to fully release the parking brake, which could have fallen into a light contact mode when you stopped hard like that.

Tech manual implies that clicking noise is a good thing.

Seat, brake, PTO engagement lever and parking brake are all the pssible hangups. Looks like the connector blocks and junctions cause problems, too.

The PTO fuse is 25 amps. Check for voltage at the fuse terminals (although you say you are getting a click. That could simply mean the PTO engagement magnet at the lever is good, but the actual clutch is not working. That magnet holds the lever in the FWD position. You might also look to see if the wire at the back PTO location has hit the crank pulley and sliced it.

Hope this helps. Stay tuned and reply when you find it. These are pretty nice machines when you get get the kinks out of them. Mine is and older one
used on a golf course and was serviced by somebody who didn't know the meaning of 'tight' for nuts, bolts, wheel lugs, or filters.

I even run a few 540 pto attachments of it when the need arises using a Rube Goldberg setup. (generator, water pump and an air compressor).

 

[CentralNC]

I appreciate all the advice from a fellow F935 owner. I enjoyed cutting with mine while it worked. I did look at all the belts and they looked fine. My F935 has a button/switch to engage the PTO and not a lever.

You have given my severeal good ideas to try when I get home. I agree that the problem is probably related to the brake in some way. Maybe I can find a way to jump the safety switch just as a test. I will report back what I find.

BTW - I saw that pto attachment that you added. Very nice!!

 

[CentralNC]

I came home from work a bit early and broke out the meter and started testing. I believe that the seat and seat safety switches are working and are not the cause of the problem. I took off the panel and tested the pto switch. It seems to work fine. All other plugs look well connected.


I listened again at the "clicking" sound I get when I first hold down that pto switch. It is not coming from under the seat. It actually seems to be coming from the pto clutch at the back of the engine. Is it possible that the clutch might be damaged or not engaging? Could a relay be malfunctioning? I tried to test for current at the black and blue plug off the pto clutch, but I was never able to read any type of current as my wife pressed the button.


I did not get a chance to ground the black wire and jump +12V to the blue terminal. I will give this a try tomorrow.

 

[zzvyb6]

OK, so now with your wife sitting on the seat (with your wallet to make it heavy enough to disengage the safeties), open the hood and start it up. Push the PTO button and see if the belts are turning the intermediate PTO shaft. If so, you might have sheared the key at the gearbox when the black double Cardan shaft connects or where the pulleys connect to the rear pto shaft.

If its NOT turning the belted shaft, you may need a new pto clutch pack because the material is worn away.

You still want to feed 12v to the PTO clutch in case there is a voltage problem and see if you can manually engage the clutch. You need Mom for this, too.

 

[zzvyb6]

Mine has a PTO brake release sensor switch on it that you may also have. This switch is intended to prevent you from engaging the PTO by other means than the PTO switch or lever. I know that sounds stupid, but that what it does. If the PTO brake band is tight, there will not be a PTO engagement.

 

[CentralNC]

I have been late in posting the results of my F935 trouble. I was cutting firewood the day after my last post and messed up my knee pretty good. It swelled up so big they had to cut my pants at the hospital.

To make a long story short .... I spent over a week doing nothing. My brother hauled the F935 to the JD dealership so I would not have the temptation to get off my butt and mess with it.

It wound up being a bad section of wiring harness and a bad switch. $211 total for the labor and parts. I picked it up myself and the guys at the shop all said that it looked like a really good mower. They have a story of one commercial mower who has over 5000 hrs on a F935. If I can get another 2 years out of mine I will be happy.

Thanks again.

 

[canucklehead]

Perfect thread!! I took my late model (newest) F935 in my 16' cargo trailer. On return trip the strap broke and the mower moved a few feet and slammed into rear cargo door hard enough to bow it out.

It now won't engage PTO for front mower. Any idea where to start or what caused this? Coincidence??

 

[pmsmechanic]

They have a story of one commercial mower who has over 5000 hrs on a F935. If I can get another 2 years out of mine I will be happy.

Man I figured when I got mine that I would never need to buy another one. Just do regular maintenance and go mow.

 

[canucklehead]

One issue I noticed with these: the motor mounts wear prematurely, causing the output shaft from engine to spin at a wonky angle. The BIG rubber bushing (JD has a different name for the bushing) takes up some of the wobble for awhile, but it stretches/stresses, cracks and lets go. Then the shaft smashes around taking out rad. I shimmed my motor mounts with large washers and the angle is proper again. You can see it when you mount shaft to flywheel area... whether it's true, or cocked at an angle.

I can't even remove my side panel to easily check the PTO switch. Is there something else that might have got jarred or disturbed to cause my PTO to not engage?