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stx38 pto switch / clutch problem fyi

Posted by erl_s (My Page) on
Wed, Jun 4, 08 at 9:34

Thanks to javert's posting below I saved a whole bunch on repairs for my STX38. My clutch would not engage so I pulled the connector to the clutch to see how much voltage was getting to it. Found I only had between 5 and 8 volts. One of the two wires going to the clutch is a ground wire going to the frame just above the clutch and was heavily corroded. Took out the ground bolt and cleaned everything with steel wool, put it back together and had a strong 12 volts. Works like new. Total cost about 1 hour of my time. Thank you very much!

Posted by javert Z8 TX (My Page) on Wed, May 23, 07 at 1:40

A member of this forum sent an enquiry about testing the PTO switch on the STX38 (which also applies to the other deck-sized STXs); the email came through GardenWeb and did not reveal the sender's address, so I decided to post the steps, as others might want to know the procedure.
First, sit in the operator's seat and turn the ignition switch on. Do not start the engine. Activate the PTO switch. You should hear a click from the PTO clutch. If you hear the click, but know that the PTO does not engage when the engine is running, then you probably aren't getting 12 volts to the clutch. Check the wires and recharge your battery.

The first test should be to unplug the wires at the PTO clutch (on the right-hand side of the tractor, behind the front wheel), then have someone sit in the seat (to activate the seat's "dead man" switch), and test for a full 12 volts in the connector at the end of the wires. If you're NOT getting 12 volts, you probably need to replace your battery.

If you DIDN'T hear the click (paragraph 2, above), then turn the key off and remove the plate on the right-side fender that holds the PTO and key switches. Pull the wire connector off the PTO switch. Be sure the key is OFF - in fact, remove the key.

Looking at the terminals on the PTO switch, note that one terminal is not in line with any of the others. Call this one "A". There are 2 terminals in the middle row; call these "B" (the center one) and "C". Drop down to the bottom row and call the one directly under "C" terminal "D". The bottom-row center terminal is "E", and the last one is "F". "A" is above "F", "B" is above "E", and "C" is above "D".

With the PTO switch in the OFF position, there should be continuity between terminals "A" and "F" (only). Now turn the PTO switch ON, and there should be continuity between "B" and "E", and between "C" and "D".

If the continuity specified above isn't correct, then the switch is bad. If continuity is OK, continue with a PTO clutch test:

With the wire connector removed from the PTO clutch, run a jumper wire from the battery's negative terminal to the terminal on the PTO clutch (where you unplugged the wires), and another jumper from the battery's positive terminal to the other terminal on the PTO clutch. The PTO should engage, and should disengage when you remove one of the wires.

If the PTO does not engage, you probably have a bad coil. Check coil resistance by removing the jumper wires and connecting an ohmmeter to the PTO terminals; resistance should be between 3 and 10 Ohms. If resistance is outside of this range, replace the PTO clutch.

In order of likelihood: 1) weak battery (or bad wires) 2) bad PTO switch 3) bad PTO clutch.


Follow-Up Postings:

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RE: stx38 pto switch / clutch problem fyi

This is definitely good info for anyone owning an STX38. I had to perform this fix three times on my STX38 in the 9 years I had it -- although once it was just the ground wire coming loose... but the troubleshooting / repair process is essentially the same.


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RE: stx38 pto switch / clutch problem fyi

Thanks, Erl, for saying "thanks." Odd thing, but late yesterday afternoon I discovered that the PTO isn't working on one of my STX's! Guess I'll have to try my own advice ... sure hope it works.


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RE: stx38 pto switch / clutch problem fyi

I have the same problem with the pto not engaging. I noticed a wire hanging down under the frame that looks like it could be the ground. If it is the ground, the bolt must have fallen out. Where exactly does the ground go? There are a couple of holes under the frame that it could be bolted to.


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RE: stx38 pto switch / clutch problem fyi

had a similar problem. The engine mount bolt that grounded the PTO black ground wire was loose- causing the pto to work erratically. To see this bolt (13mm i Think) you will have to lie on your back and look under the machine. It is above the front steering arm of the right tire. If the wire is dangling you will need a new bolt. Thanks for the previous posts ;)


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