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Discussion Starter #1
Hi,

First time poster here looking for some advice. I purchased a "beater" STX38 at the beginning of the summer for 200 bucks hoping it would get me through til the prices came down in the fall and I might make a more long term investment. Well, the **** thing ran like a champ all summer and I just might keep it. That was until last week.....

It is the black deck, 13hp, hydro version, by the way. The seat switch was by passed when I bought (actually, the entire seat was missing), but both the brake and PTO switched operated correctly.

It always started first crank. When I started it last week, I was distracted and flooded the engine. Rather than wait, I kept cranking and it finally started, and I mowed half the lawn. When I tried to restart it a little later, just got a click from the solenoid. After about a hundred tries, it cranked, started, and I started mowing. After about 20 minutes, it stalled, and another hundred key turns to get it started. Here is where it gets interesting....

As soon as I took my foot off the brake, it died. If I leave the brake on and engage the PTO, it dies. Leave the brake on and the PTO off, it will idle for hours. I can catch the engine from dying by quickly depressing the brake or turning the PTO off.

Since I cranked it so heavily trying to start after I flooded it, I think I burned out some switch or maybe the solenoid. What I don't understand is why both the brake safety AND the PTO safety are BOTH killing the engine - are they wired together? In a normal machine, can the PTO be engaged with the brake on?

Any thoughts on what I should replace? Could the prolonged cranking when it was flooded have burned a wire from high amps? Or is this just a bad solenoid that had a safety switch go south too?

Thanks,

Lou
 

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Lou; On the Backyard Round Table forum portion of MTF is a post by Brad about starters on STX38 and other tractor. He has had very good success with the fix as have other, so read it and see if it help you with your problems any.

Dick

First of all, it's with the blessing of the moderators that are assigned to this section that I am posting and sticking this thread.

I have a John Deere STX38 that has been plagued with the starting problem that seems to be inherent to that machine. You turn the key, and you get the good old "click" from the solenoid. A small smack on the starter with a nearby tool (screwdriver handle, hammer, spade, etc.) would generally make the starter engage and turn over. I tore the starter apart several times, cleaning, lubing, etc. trying to find/fix the problem, to no avail. Then, somewhere, I read a post about the availability of a "Starter Assist Relay" that was sold by John Deere to fix this problem. Price was somewhere in the neighborhood of $25. Well, that was a bit steep for me so I went about searching for a less expensive alternative. I found a post on another forum telling of fabricating a similar item for Volkswagon automobiles with the same issue. I decided to try and build my own. Subsequent to my original post in the John Deere section, others have approached me for a copy of my schematic for different models of John Deere and different brands of machines. The cause of this situation is that over time the different safety relays get corroded, connections get corroded, batteries are still good but put out less than optimal voltage. This alteration does not in any way bypass any of the safety switches on your machine. If you could not start your tractor because of a safety issue prior to installation of this relay, you still will not be able to start it.

Well, the first thing in this project that I needed was a relay. Plain, old relay. The kind that every auto on the road has 6 or 8 of. I went to a name brand auto parts store, with the design of the relay drawn out on a sticky note, so I could tell them what I needed. When I walked in and told them what I was looking for, so I could build a project for my lawn mower, I got the old "Deer (not Deere) in the headlights look".

"I don't think we carry lawnmower parts like that."

No, I said, I need an auto relay, it's for a project I am building for my lawnmower.

"Here's all our lawnmower parts. See, we just carry spark plugs."

No, let's start over. Do you sell auto relays, like for horns, lights, fog lamps, etc?

"What kind of vehicle?"

It doesn't matter!

"Well, we sell trailer light kits for about $25 over here."

We go over there and he shows me the light kits. Right next to it was a relay just like what I wanted for $3.95ish. I'll take this. It's just what I need.

"Do you think that will work in a lawnmower?"

Anyway, I take my purchase home and begin my assembly. First thing I notice is my shortage of different colors of wire. I thought about going back to the auto store, but I am pretty sure they didn't sell "Lawnmower wire" there, so I compromised. I cut 4 lengths of wire about a foot long each. Put some female spade connectors on 1 end of each wire, attached them to the relay. Then, I read my directions and compared them to the info on the back of the relay package and figured out my next step. I labeled all the wires (ground, 12v, key, solenoid) and started my installation.

I don't know about you, but whenever I work on something and it's time to give it the old "college try", I am a bit nervous about the outcome. I always dread that my work was for naught, and when I prepare to see if I made any difference in my machines operation I always fear the worst. Well, I plop myself right down on the seat, make sure that the PTO switch is off--check, in neutral--check, turn the key--NOTHING. Oh, I forgot to re-attach the battery. Fixed that, let's try it again. Sweaty hand reaches down to the key turn it to the "START" position, and bingo! Turns right over! Oh, well, that had to be a fluke. It was just luck. Gotta try it again, just to be safe. Sure enough, turn the key and away she goes. Oh, boy. I gotta get some pictures of this and post 'em on MTF. This is really gonna be a hit! And, it appears, it was a hit. I have had many requests for this schematic since the original post and about everyone reported a success after installation except 1 fellow, and I think that he did figure out the problem. So, here is the schematic for the starter relay, along with a link to my original post, in case you have any questions. If you click on the relay, you'll get a larger image that you can print out. If you have any problems or need further info, just PM me or drop an e-mail and I'll see what I can do to help you out. Have fun, and be sure to report your results!

Thanks to member Wayhaw, I have a .doc file that will help a few folks with better descriptions and explanations. Let me know if you need a copy of this. Please include your e-mail address.

Original Post--Click Here
 

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Discussion Starter #3
Although I appreciate the recommendation for the additional solenoid, I decided to try some fundemental things first. I ran all the accessible wires, cleaned and re-made all frame, solenoid, and switch connections.

As I mentioned, the seat safety had been disabled, so I removed the electrical tape and found two white wires connected to a single spade connector, and a black wire connected to nothing. Stupid me connected all three wires - started, but died when the brake was released. Read some more on the web and discovered that thye switch is "normally open" and the two white wires should be connected and the black left unconnected.

It started and ran.

Now the weird part. The PTO pully was turning even though the switch was off.

I shut it down and decided to look at it again the next day.

When I went to start, I heard a pop by the PTO - the connector was melted.

My question is as follows: When I disconnected the PTO plug to clean, I didn't think to check polarity - thought the plug was idiot proof. Not so. So I might have plugged the PTO in backwards - hot to ground and vice versa.

DOES ANYONE HAVE A BLACK STX38 WHO CAN TELL ME WHICH TERMINAL THE BLUE WIRES CONNECTS AND WHICH ONE THE BLACK CONNECTS????

The PTO faces forward, so one connector is toward the machine center and one terminal is toward the outside. A picture would be great.

Another possibility is when I bound all three wires for the seat switch incorrectly, I smoked the PTO switch, which is why it was running when the switch was off, and the plug melt was somehow related - can't understand how, but I am out of answers.

Thanks,

Lou
 
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