john deere stx38 pto switch shuts off engine

11 years ago

I originally found the forum topic labeled 'stx38 dies when pto engaged - old man needs help!' And, being it described my issues, followed the instructions that solved his problem but, it didnt work for me.

Here's my problem with my JD STX38. When I engage the PTO to activate the blades, the engine dies after 5-6 seconds. At first the blades would turn, now after working on this for a couple days the PTO switch doesnt turn or activate the blades anymore and there is still that 5-5 second delay until the engine dies.

Here's what Ive done so far, Bypassed the PTO switch but still got the same result of engine shut off. Checked connections & wires for wear grounding etc but am now at a loss, short of buying a new PTO unit & going through all that for this old JD. I would be more liable to buy a new mower in that case as this has its issues & shortcomings even when working.

Any ideas out there? Remember, this has been running fine since I owned it (1 1/2 yrs) & I made no changes to anything that precipitated the engine shutting down shortly after activating the PTO.

Thanks in advance for te help. I'de hate to scrap this little green & yellow mower.

Featured Answer

sswinehart

11 years ago

The PTO clutch on the tractor is electro-magnetic and takes a lot of current to operate. If you have a low battery condition this will stop the tractor because you don't have enough voltage to run the ignition system with the PTO turned on.

First, check the battery voltage with the tractor off. You should have about 12.75 to 13+ volts (depending on the age and condition of the battery).

If the battery voltage is low you could have one or more of the following problems:

1. Old battery that will not hold a charge - needs replacement.

2. Bad voltage regulator - battery is not being charged and electrical system is running on low voltage when the engine is on and the PTO draws enough to shutoff the tractor.

3. Bad stator - battery is not being charged.

Of the three possibilities - 1 & 2 are the most common. A bad stator is the least likely but, you can easily narrow this down.

Start the tractor and check the battery voltage. If the stator and voltage regulator are working correctly, you should have 14+ volts at the battery. If you do not have 14+ volts with the motor running, then the battery is not being charged - and there is probably not electricity being supplied to run the electro-magnetic PTO clutch + ignition.

You can sort this out by starting the engine and pulling the connector from the voltage regulator and looking for AC voltage using a multi-meter. I do not know the exact terminals on that engine - but, you should be able to find a service manual on line in electronic format for about $8.00. Otherwise, you can do this by a process of elimination. Put the probe in the top left contact and check the other contacts sequentially. What you're looking for is about 30 Volts AC from the stator. Then go to the second contact, repeat, etc. If you don't find the voltage - bad stator. This really isn't as likely as a bad voltage regulator.

Voltage regulators have diodes in them and other semi-conductors and after being continually exposed to heat, vibration, etc. - they go bad.

So, check the voltage regulator with a multi-meter on the Ohms setting. Most of the resistances should be in the 4.5 mega-Ohm area. If you find opens or low Ohm readings between contacts on the voltage regulator - it needs to be replaced. My guess - it's the voltage regulator and you will find several "open" conditions.

I just replaced the voltage regulator on a John Deere garden tractor because the PTO would not stay engaged and the battery was always low.

If you find the voltage regulator is bad, in your case I would replace both the voltage regulator and battery if the battery is over 2-3 years old as constantly running it in a discharged state has probably compromised the battery's ability to hold a charge.

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Comments (6)

javert
11 years ago
Barry - Good advice from Buckhorn (above). ALSO, check the ground wire that is attached to the underside of the frame behind the right front wheel. It's just a thin little wire that is screwed to the flat part of the frame in the area near the PTO mechanism itself - make sure it's clean and firmly attached.
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Hey folks, so I'm posting this follow up in my original thread because I think I have a related problem. Last year, I replaced the PTO drive belt and the mower blade drive belts on my inherited JD STX 38 Yellow Deck. Today I took the mower out (NOT the first time this season) and had some serious issues. First of all, the grass is tall - 18-24 inches. I had the mower height set to the tallest height. The grass may have also been slightly damp - although not wet. I was able to cut basically one path, then I realized that although the PTO was engaged, the blades weren't cutting the grass. I was going at the slowest speed (first gear) and even tried cutting using only 1/2 of the mower deck width at a time - no help. I took the mower back to my driveway, cleared out lots of old clumped grass from the blades, and started the mower and the PTO. The blades were definitely turning. I turned off the mower again, and noticed that the PTO drive belt is looking terrible - it's all pitted and slack - it's not tight around the PTO shaft! So, my theory is this: the PTO drive belt is shot again (Although not broken yet) - so the blade spin when I'm not trying to cut anything, but when I come in contact with any sort of grass of substance, the slack belt is "slipping" and resulting in the blades not cutting? Does this make sense? Solution: replace the belt AGAIN???? A few more things to note: 1) I tried cutting shorter grass and drier grass and had very little luck. 2) why would my PTO drive belt, just replaced a year ago, be so shredded already? That's worrisome... any advice would be appreciated. thanks.
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BarryBob
Original Author
11 years ago
What a an idea & boy does that make sense. I didnt mention that I did change the regulator but the machine does have a worn out battery. I'm going to skip the wire testing (cause I blowed up me tester oops)& put the charger on the battery & leave it there while running just to see if the PTO will come back to life & spin the blades. I've managed to get those clamps to hold & stay on under the seat without sparking before so... if this works & the machine stays running, I should just get a new battery? This one is played anyway with multiple dead clicks before actually turning the motor over, or, should I get a new tester & check those numbers before hand?
Thanks for the smart thinkin. Barry
bill_kapaun
11 years ago
I find it difficult to believe that your battery would have enough capacity to start the engine, but a 5 AMP draw from the PTO would "starve" the battery to the point that the carb fuel solenoid (not the ignition) would kick out and kill the engine within 5-6 seconds.

Is the engine killing 5-6 seconds after engaging the PTO?
OR
Is the engine "killing" immediately and then taking 5-6 seconds to quit rotating after you pull the PTO?

My guess is the later and stems from a bad/misadjusted seat switch.

I don't have a schematic for that tractor, so I can't give specific troubleshooting advice.
89tango
10 years ago
I have the same problem on the same mower-stx38 yellow deck. I've changed the PTO switch, installed a new battery, checked voltage and have 14.75 when engine is running, so voltage regulator seems to be ok and I've cleaned all grounds and set the gap on the clutch as near as I can to .018. What's next--change the clutch?
89tango
10 years ago
I might add, unlike the problems from BaryBob, my mower runs and cuts for several minutes and then shuts off. With mower not running, I have 12 volts down to the PTO and as I said above, I just put in a new battery and when running I have 14.+ volts at the battery so it is charging.

john deere stx38 pto switch shuts off engine

sswinehart

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javert

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john deere stx38 pto switch shuts off engine

sswinehart

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javert

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