STX38 PTO is probably bad. Your opinion.

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  #1  
Old 09-09-14, 08:08 PM
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STX38 PTO is probably bad. Your opinion.

Hello,

A couple weeks ago the blade/PTO stopped engaging on my 90's John Deere STX38 (Yellow Deck). After trying to do as much research as I could I did the usual tests.

I checked the ground wires under the frame near the right front wheel. With the key on and motor not running I turned on the PTO switch and listened, but did not hear a click. I disconnected the PTO wires from the clip (the one located under the starter on top of where the wires go through the body and below) and first tested with a test light to make sure it was getting power. I used a multi-meter to find I was getting 12.4 volts between the + and - of the battery. Then I tested the voltage at the end of the clip and found it to be 12.4, so I knew everything was OK (switch, safety switches, etc) all the way down to where the wire clips together.



I then used two jumper wires straight from the battery to the end of the clip that goes to the PTO. I tested the wires with a test light to make sure they were making contact. When connected the PTO made no clicking noise and it could be easily turned by hand in all situations.



Here are the wires that go from the clip to the PTO, and you can also see just a small part of where the ground wire attaches to the frame.



Does this pretty much confirm that my PTO is bad? I've seen something about an "air gap" mentioned, but I don't understand what that is referring to. Would I have to replace the entire PTO or can it or part of it be rebuilt? Is there anything else to check?

Thanks,
 
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  #2  
Old 09-09-14, 10:33 PM
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Check the wires that go into the clutch. Often, one of them breaks just before it enters the clutch coil. The air gap is adjusted by those 3 nuts on the clutch. If the gap is too large (happens over time), the clutch can't pull in. If you can help the clutch pull in by applying voltage and then lifting the clutch plate with a screwdriver, then the clutch is good and needs adjusting. How many ohms do you measure between the clutch wires?
 

Last edited by cheese; 09-12-14 at 09:14 PM.
  #3  
Old 09-12-14, 06:26 PM
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Thank you for the reply, Cheese. I'll check the ohms this weekend and get back to you.
 
  #4  
Old 09-14-14, 04:52 PM
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I pulled the PTO off. It was very easy. I attached a breaker bar to the top of the engine, had my wife hold it and took the bottom nut off of the PTO relatively simply.

I checked the checked the Ohms on the harness and it read 0, which basically means I'm getting nothing. I doubled checked with continuity and got nothing, even when I tried the probes a little deeper where the wires actually connect to the PTO I got nothing, so it sounds like I need a new (good used) PTO.

I'll check online. When I get one and put it back on I'll get back and let you know how it goes in case anyone needs to use this thread to help in the future.
 
  #5  
Old 09-25-14, 05:22 PM
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Hello everyone,

Thank you for the replies and the help diagnosing my problem. After using the advice from this and one other forum I was able to diagnose that it was definitely the PTO that was faulty. I bought a used one from Ebay. I first plugged it in and tested it and it heard a loud click that was missing from my old one. I installed it and at first my heart sank because it didn't work, but then I realized I'd had forgotten to plug it back up the second time. After that it worked perfectly.

One question I had: I looked online and found lots of information about removing the PTO, but I didn't find anything about removing the belt or replacing the belt. I unbolted the PTO and the belt slid off with it. When I put it back on I just put the belt around it and slid them on together. There didn't seem to be a problem, but is this an OK way to reinstall it?

Also, for anyone else installing one, at first I didn't see the peg/pin in the rear that needs to slide through a hole in one of the "wings." I couldn't get the PTO to slide all the way up and by this time it was dark outside. I finally found an angle where the peg/pin was visible and after lining it up (and the bushing above it) it slide right on with no problems. I tightened everything up and for the very last bit had my wife hold a breaker bar on the top bolt while I tightened from below.

Thanks again,
 
  #6  
Old 09-25-14, 09:04 PM
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Glad you got it. If you were able to put the clutch on with the belt on it already, the belt must not be very tight... it usually has pretty good tension on it.
 
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