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post #1 of 12 Old 08-08-2019, 11:23 AM Thread Starter
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JD 318 PTO will not engage - bad connections

OK, I feel stupid for asking because I've seen many many posts where some one has answered this, but I'm getting tired searching thru posts to find those responses. So my apologies ahead of time.

Two weeks ago I threw the PTO switch and the PTO didn't engage. The PTO light on the cluster did not come on either. I began troubleshooting by checking for voltage to the PTO coil - no voltage. As I was about to start checking other things, the PTO just pulled in...and held in while I mowed. I figured I hadn't seen the last of the issue...

Last night I was one minute away from finishing and the PTO cut out. Again, the PTO indication on the cluster was out, so I'm quite certain that the clutch and coil are not the issue. It's not the seat switch because the engine starts and runs. It was getting dark, so I didn't check anything yet. I assume I'm looking for a bad connection or bad ground wire. Can you name any particular connections or places to begin looking?
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post #2 of 12 Old 08-08-2019, 12:04 PM
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Re: JD 318 PTO will not engage - bad connections

The seat switch is "involved" in the pto circuit also. I believe if you get off the seat (for maybe 1 second?), the pto shuts down. I'd start there.

We don't allow description of bypassing safeties I've edited them out of this post. The above statement it correct, the TDM will shut down the tractor if you take pressure off the seat switch.

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Last edited by PA318Guy; 08-08-2019 at 03:58 PM. Reason: Deleted detail for bypassing safety
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post #3 of 12 Old 08-08-2019, 02:23 PM
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Re: JD 318 PTO will not engage - bad connections

In addition to what has previously been said, check to make sure your battery is up to par. I had a JD that would start fine, but with engine running, and then engaging pto, would shut the tractor down.
Replaced the battery, all was well.
Just a thought.
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post #4 of 12 Old 08-08-2019, 04:02 PM
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Re: JD 318 PTO will not engage - bad connections

Have you checked the gap on the PTO? The gap is supposed to be .018 and if not set correctly will cause PTO to disengage when voltage drops. However, I agree that you may want to check your battery and ensure a full charge before using PTO. Your Voltage Regulator may not be returning enough electric to the battery to keep it charged while running, this will also cause the symptoms you provided.

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post #5 of 12 Old 08-08-2019, 08:38 PM
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Re: JD 318 PTO will not engage - bad connections

Quote:
Originally Posted by CantKeepUp View Post
OK, I feel stupid for asking because I've seen many many posts where some one has answered this, but I'm getting tired searching thru posts to find those responses. So my apologies ahead of time.

Two weeks ago I threw the PTO switch and the PTO didn't engage. The PTO light on the cluster did not come on either. I began troubleshooting by checking for voltage to the PTO coil - no voltage. As I was about to start checking other things, the PTO just pulled in...and held in while I mowed. I figured I hadn't seen the last of the issue...

Last night I was one minute away from finishing and the PTO cut out. Again, the PTO indication on the cluster was out, so I'm quite certain that the clutch and coil are not the issue. It's not the seat switch because the engine starts and runs. It was getting dark, so I didn't check anything yet. I assume I'm looking for a bad connection or bad ground wire. Can you name any particular connections or places to begin looking?
Quote:
Originally Posted by PA318Guy View Post
Have you checked the gap on the PTO? The gap is supposed to be .018 and if not set correctly will cause PTO to disengage when voltage drops. However, I agree that you may want to check your battery and ensure a full charge before using PTO. Your Voltage Regulator may not be returning enough electric to the battery to keep it charged while running, this will also cause the symptoms you provided.
PA318Guy has it nailed. My '84 318 was doing just what you described, and after reading his sort of answers, I re-gapped my PTO and problem solved.....pretty much. Mine will engage after I first start up, and will stay engaged for as long as I want to mow, as long as I don't turn the PTO off after the engine has warmed up. Once I do that, I have to stop and let the tractor cool down before it will engage again. I attribute that to the gap closing too much as the PTO heats up, so I may see if I can open the gap a tiny bit, but I set it as close to 0.018 as I could get. I may just have to be happy a 35 year old tractor still works at all.

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post #6 of 12 Old 08-09-2019, 09:26 AM
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Re: JD 318 PTO will not engage - bad connections

Quote:
Originally Posted by KHodges View Post
PA318Guy has it nailed. My '84 318 was doing just what you described, and after reading his sort of answers, I re-gapped my PTO and problem solved.....pretty much. Mine will engage after I first start up, and will stay engaged for as long as I want to mow, as long as I don't turn the PTO off after the engine has warmed up. Once I do that, I have to stop and let the tractor cool down before it will engage again. I attribute that to the gap closing too much as the PTO heats up, so I may see if I can open the gap a tiny bit, but I set it as close to 0.018 as I could get. I may just have to be happy a 35 year old tractor still works at all.
My 318 has been doing this exact thing lately as well. Although the PTO dash light comes on for me so a slight difference from your symptom CantKeepUp. I was suspecting a bad PTO switch or connection but I will have to go verify my PTO gap hasn't deviated from the last time I adjusted it.

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post #7 of 12 Old 08-09-2019, 10:10 AM Thread Starter
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Re: JD 318 PTO will not engage - bad connections

My analysis is:

1. Not the seat switch because it has a single contact going to the TCM (the TDM uses that for logic to the engine run and PTO command). If the switch was stopping the PTO, the engine should also stop.
2. Not the battery because when I was initially troubleshooting it, I verified zero volts to the PTO coil. I think a low battery would just give me low volts (not enough to pull in PTO)
3. Not the gap for the same reasons as #2 (zero voltage witnessed at PTO).

edit - just looked at elec diagram. The PTO coil and the cluster PTO Lamp share the same signal. Since my lamp isn't coming on either - supports no voltage diagnosis

Anyone disagree?

edit 2 - looking at the elec schematic, I guess I'll start by seeing if I have voltage from the TDM to the PTO switch (/60 BLU wire) and go from there. Busy moving kids into college, so it might be a few days before I get back to it.

Last edited by CantKeepUp; 08-09-2019 at 10:25 AM.
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post #8 of 12 Old 08-09-2019, 11:08 AM
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Re: JD 318 PTO will not engage - bad connections

I would also check both molex connectors, clean and make you you get continuity between both sides of the connector. Check the grounds too.

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post #9 of 12 Old 08-09-2019, 01:40 PM Thread Starter
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Re: JD 318 PTO will not engage - bad connections

RussKish - that's the feedback I'm looking for. When you say both Molex connectors and grounds - where? All in the space between the console and the battery?
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post #10 of 12 Old 08-09-2019, 07:49 PM
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Re: JD 318 PTO will not engage - bad connections

Quote:
Originally Posted by CantKeepUp View Post
RussKish - that's the feedback I'm looking for. When you say both Molex connectors and grounds - where? All in the space between the console and the battery?
We will start with the grounds.

1.)- Front PTO may have one, it should go to one of the engine mounting bolts, plus check all engine mounting bolts.
2.)- Top of engine, left side will be the battery ground, there maybe another there also (mine has it there too)
3.)- Inside the right side pedestal under the auto reset circuit breaker on the frame of tractor.
4.)- Rear left side between the seat pan/frame support for the rear lights
5.)- Only if you have the rear PTO option: right side inside frame with the support arm for the rear PTO clutch

Molex connectors is how the TDCM is connected to the wiring harness, it is located under the battery and battery tray. The TDCM is mounted to the steering outer shaft.

Warning!!!!! When checking continuity on the molex connectors, please disconnect the Battery!!!!!

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post #11 of 12 Old 08-10-2019, 02:28 PM
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Re: JD 318 PTO will not engage - bad connections

My Craftsman had same issue. No PTO, or would work intermittently. Mine was simple. I'd pull the PTO switch up while pressing forward on it. That would work. Just operating it normally got nothing. After a while, no amount of wiggling or anything would make it work. Bought a replacement switch that solved the problem, and has worked for years without issue.

Maybe suggested already, but check for power to the switch when all else is in "go mode". If power in but none out with the switch in PTO position, it's the switch.

As AVE says, its where the gorilla meets the pixies, a most vulnerable device.

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post #12 of 12 Old 08-11-2019, 01:47 PM Thread Starter
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Re: JD 318 PTO will not engage - bad connections

Thank you RussKish!

Yep - it was the connector for the TDM. I could wiggle it to get the PTO to click in. I seems reliable now with cleaned up connections.

BTW - for 318 owners, the TDM connector is under the battery, but for the 318, it is accessible from the right side if you remove the little cover. Wish I had realized that before removing the battery and cursing JD engineers for stuffing all the wiring in tight spaces. Wish my 317 had that.
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