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Thread: JD lawn mower problem

  1. #1
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    JD lawn mower problem

    A long shot, maybe the BFF Brains Trust can help.

    JD STX38, black deck model, no model numbers (apart from the Kohler engine numbers) to be found, but there is a date on the underside of the seat which looks like Aug 9 1996. Google brought up numerous refs from Yankeeland, and reading them it seems there is a multitude of variations for the STX38.

    Problem: mowing normally for about 10 mins., and the engine dies. Push in foot clutch (i.e. transmission clutch, one pedal only, right hand side) and switch off mower blades' electric clutch - engine starts & runs normally.

    Foot clutch disengaged, engage electric clutch - engine dies.

    Leave electric clutch off, leave foot clutch disengaged, engine starts, engage foot clutch - engine dies.

    Engage park brake (which holds the foot clutch disengaged), engine starts, disengage park brake, engage foot clutch - engine dies.

    Jumper seat safety switch and test above - no change.

    My assumption from all above is that there is a safety switch on the park brake, and it is in series with the seat safety switch - i.e. if either one is open, engine dies.

    Does that sound reasonable, and if so where is park brake switch? Not being funny here - it's not easy to see & feel much without turning the machine upside down!

    The US sites suggest checking the chassis earth. Found it (not where it is supposed to!) and it is tight (didn't lay a spanner on it to check - would have to remove a back wheel to do that).

    Found two different wiring diagrams, but with no serial number it is hard to decide which one to use first - apart from the problem of claimed numerous variations.

    Tried an online tech, but for the cost of AUD59 I might as well take it to the local workshop.

    Any thoughts anyone?

    JV
    Agtronix - the home of the Weedswiper

  2. #2
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    Re: JD lawn mower problem

    On further thought, my proposition that there are switches on both the seat and the park brake is invalid. The engine must run no matter the position of the park brake. Ditto the transmission clutch; the engine must run whether it is engaged or disengaged. It now seems that the only possible problem locations are the clutch switch ( the wiring must be intact coz the blades turn when the clutch is engaged, before the engine stops) or the seat safety switch - in which case, why does jumpering that switch not eliminate the problem? And why do two normally separate actions i.e. engagement of the mechanical and the electric clutch produce the same failure mode?

    Tomorrow I'll take the cover off the switch panel and look for anything suspicious.

    JV
    Last edited by john maddock; 14-04-17 at 02:36 PM. Reason: typo correction
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  3. #3
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    Re: JD lawn mower problem

    Some progress today. Established that there is no switch on the park brake; it is a simple mechanical latch which holds the depressed clutch pedal at the end of it's travel in the brake position. The switch is activated by a lobe on the clutch pedal when it is in the brake position.

    Extracted the key and electric clutch switches from their mount. Nothing unusual to be seen, but I remembered that on some occasions the key switch has failed to stop the engine.

    The major breakthrough was to discover a comprehensive tech manual by JD on Google docs. It shows the various test points on wiring connectors, and hopefully will lead to the problem.

    JV
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  4. #4
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    Re: JD lawn mower problem

    Do you have mice there in Taz John? buggers pee on stuff including electrical connections which don't take kindly to it, plus as I confirmed again this week with the farms big ride-on just stiffing it in a dark barn overwinter C/W abundant nesting materials is asking for trouble
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  5. #5
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    Re: JD lawn mower problem

    Quote Originally Posted by Footsfitter View Post
    Do you have mice there in Taz John? buggers pee on stuff including electrical connections which don't take kindly to it, plus as I confirmed again this week with the farms big ride-on just stiffing it in a dark barn overwinter C/W abundant nesting materials is asking for trouble
    Too right we have mice! Native ones, as well as the imported, common house mouse - and this is the time of year they begin to move in from the paddocks.

    Take your point re mouse piss - not to mention possible chewed wires. It's rather hard to see into the gizzards of said machine, so I can't be sure that there isn't a chewed wire somewhere. I've pulled several connectors which are easily got at & all look normal, as do all the wires I've been able to see. Without any tests done according to the book (which I might get to tomorrow) I'm inclined to suspect the key switch. Because it worked normally for 10 mins before quitting, maybe machine vibration was a factor. I think this story has legs, with more to come.

    JV
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  6. #6
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    Re: JD lawn mower problem

    My rideon experiences are all 1970's & earlier Wheelhorses, but they tend to have three safety switches - one for mower PTO, one for neutral, or clutch depressed & one on the seat. My bet would be one of these failing intermittently.

  7. #7
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    Re: JD lawn mower problem

    Quote Originally Posted by pycoed View Post
    My rideon experiences are all 1970's & earlier Wheelhorses, but they tend to have three safety switches - one for mower PTO, one for neutral, or clutch depressed & one on the seat. My bet would be one of these failing intermittently.
    Yes, this mower has the three switches also, and I agree it is likely one of the three has failed. Without having done the tests yet, I think the culprit will be the key switch. We shall see.



    jv
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  8. #8
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    Re: JD lawn mower problem

    I wuz wrong! Not the key switch; it's the PTO switch which is the culprit!

    Without the workshop manual from Google Docs I would have been stuffed (to coin a phrase).

    Because on occasions in the past the key switch had failed to stop the engine, I was confident that would be the culprit. Not so. In the "off" position the reading is 140R, but in both the "on" and "start" positions the readings are 1R5 and 1R0 respectively.

    The PTO switch is a different matter: in the "off" position, the resistance of the two relevant pins varies from about 50R to 200R, making that circuit questionable, whereas the circuit when the switch is "on" is open, when it should show minimal resistance.

    Obvious next move is to obtain a new switch when the JD dealer opens, and with that fitted, the problem might be fixed. Maybe.

    The switch is a Delta Systems Inc. switch, but the number on the switch I have does not match with any on their website, so I spose it's a JD special.

    JV
    Last edited by john maddock; 16-04-17 at 11:26 AM. Reason: more info
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  9. #9
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    Re: JD lawn mower problem

    Well, I wuz wrong again .

    In consideration of my proclivity to accept the first obvious solution and then get on with the next thing to be done, I thought it would be wise to do the other checks listed in the tech manual. Surprise, surprise, all the cabling tested normal.

    What to do? Put the switches back & see what happens. Bigger surprise: the engine started as normal; the mower moved as normal; the blades rotated as normal. Just another ∞¢ª•ª≠–ºª°‡°‡fi intermittent!

    To check further, I tested the continuity of the PTO switch pins again, and got the same results as yesterday: open circuit across 2 pairs. Then it dawned that maybe I’d misunderstood the instructions:

    “PTO switch OFF continuity… terminals (A and F).
    PTO switch ON continuity … terminals (B and E) and (C and D)”

    I took that to mean that B and E were commoner internally, ditto C and D, and had tested the 4 terminals as one pair. Wrong! B and E are one pair, C and D are a separate pair, and when tested accordingly, are ok.

    So the problem is just another ‹‚·flfl‹›°‡ intermittent.

    Or to put it another way, when testing the PTO switch of a JD mower ensure that Murphy’s Law 34 Part 2 (1) is observed and steered clear of.

    JV
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  10. #10
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    Re: JD lawn mower problem

    Well, I wuz wrong again .

    In consideration of my proclivity to accept the first obvious solution and then get on with the next thing to be done, I thought it would be wise to do the other checks listed in the tech manual. Surprise, surprise, all the cabling tested normal.

    What to do? Put the switches back & see what happens. Bigger surprise: the engine started as normal; the mower moved as normal; the blades rotated as normal. Just another ∞¢ª•ª≠–ºª°‡°‡fi intermittent!

    To check further, I tested the continuity of the PTO switch pins again, and got the same results as yesterday: open circuit across 2 pairs. Then it dawned that maybe I’d misunderstood the instructions:

    “PTO switch OFF continuity… terminals (A and F).
    PTO switch ON continuity … terminals (B and E) and (C and D)”

    I took that to mean that B and E were commoner internally, ditto C and D, and had tested the 4 terminals as one pair. Wrong! B and E are one pair, C and D are a separate pair, and when tested accordingly, are ok.

    So the problem is just another ‹‚·flfl‹›°‡ intermittent.

    Or to put it another way, when testing the PTO switch of a JD mower ensure that Murphy’s Law 34 Part 2 (i) is observed and steered clear of.

    JV
    Agtronix - the home of the Weedswiper

  11. #11
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    Re: JD lawn mower problem

    john - make a temporary by-pass for the suspected switch(s) and include an indicator light on the leads - you can then test the machine and if the problem goes away when the switch is "hot wired". . . . but if the light goes out it indicates something else within that circuit.

  12. #12
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    Re: JD lawn mower problem

    Quote Originally Posted by Ironhead View Post
    john - make a temporary by-pass for the suspected switch(s) and include an indicator light on the leads - you can then test the machine and if the problem goes away when the switch is "hot wired". . . . but if the light goes out it indicates something else within that circuit.
    Good thinking Ironhead. I'll keep it in mind for when the problem next appears.

    JV
    Agtronix - the home of the Weedswiper

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