2006 NH TC55DA clutch disengages randomly

[FarmaBro]

2006 TC55DA w EHSS

Ladies and Gentlemen,

After spending too much time troubleshooting everyone's favorite type of problem (intermittent), I am out of ideas and so I come seeking the collective knowledge of this community. Please bare with me while I try to explain.

While travelling, the clutch randomly disengages and in order to resume motion, I must depress the inching pedal. I know that this pedal operates both a potentiometer and a dump valve so I manually actuated each and found that it is pushing the pot through it's full range of motion (or most of it) that permits driving again. This leads me to believe the EHSS controller may be getting a bum signal from something. It may think the tractor has just been started or the operator has left the seat.

I don't believe the problem is the seat switch because I first noticed this when hogging my field and the engine should turn off when the pto is running and the operator leaves the seat. Also, my seat switch is broken and bypassed.

I believe the clutch is physically fine because it feels very grabby when I engage it hard via the pedal but also, I can stall the engine by pressing the breaks.

I don't believe the problem is hydraulic pressure because I don't find the problem is exacerbated by operating the pto and loader while travelling.

I checked the potentiometer and found the resistance changes relatively smoothly throughout it's range of motion from ~200ohm to 1.4kohm. It's times like this when I wish I had an old style multimeter with a needle. I don't know what these values should be but my measurements were repeatable.

System voltage is >13V while running. I expect the electronics should operate just fine between 10V - 14V

Oil is clean and full with a brand new filter.

My inspection revealed no damage to any wires. Ground lug is in good condition and when I pulled on the wiring harness while driving, I could not cause the problem to manifest in a repeatable way.

I have a service manual on order but it won't arrive until next week. Hopefully it can give me more insight into how the various systems operate. A more reasonable person would wait but I can't let it go. I'm not satisfied without understanding.

If I have made any incorrect assumptions, please correct me. If anyone has insight to share, I sure would appreciate it.

 

[FarmaBro]

I was able to reproduce the behavior by turning the key very briefly out of the "run" detent toward "off". After removing the switch, I found the resistance values to be all over the place so I disassembled it and cleaned the contacts. Now the switch has very low resistance but the problem persists. Tomorrow I'll start working my way downstream.

Is this a bona fide clue or just a red herring? I don't know but I have to try something.

 

[LouNY]

I would expect that the potentiometer ends up providing a 0 or 1 v to 5 volt signal to the control,
so anything that any bouncing which could cause a brief voltage loss could cause your behavior.

 

[FarmaBro]

Today I made it as far as the fusebox, so not very far. It's interesting how they chose to mount it against the firewall because it makes it very difficult to access, especially with a loader installed. It was filthy so I cleaned it out and replaced a melted fuse feeding the road lights. Of course everything there checked out okay.

One positive update is that the problem is worsening. Now instead of intermittently failing, it's intermittently working. Tomorrow I might just test the life out of it in the hopes of making the problem easier to find.

If nothing else, this thread will act as a journal so I can remind myself what I've already done.

 

[Ford850]

This sounds like a good challenge and I’m looking forward to following along.

 

[FarmaBro]

I thought I was so smart measuring "on" 12v line to ground looking for a short. Of course what I measured is the combined parallel resistance of every light and relay coil connected to that line, so just about everything. It was foolish to start poking at things hoping a problem will jump out at me. I needed a better plan and a better understanding of what I'm looking at.

Today I scanned and printed out the wiring diagram from my operator's manual so I can draw all over it. Now having identified everything touched my the suspect line, I think I can isolate and test each wiring harness but that will have to wait for when I have more light and less cold.

If anyone has any advice, I'm all ears.

 

[FarmaBro]

Progress Report:

I'm confident I found the culprit. There's a switch on the side of the transmission that tells the computer if it's in gears 1-2 (on) or 3-4 (off). It turns out my tractor works just fine in gears 3 and 4 and I just never bothered to try them.

After checking the switch operation from the ehss controller connector with my ohmmeter, I saw inconsistent values like crazy. I spent a good 20 min just verifying my setup before reproducing my results at the switch connector under the tractor. That's when it occurred to me to try the higher gears. Furthermore, when I did try 1-2, the behavior where I had to pump the inching pedal resurfaced. I could finally break it in a way that made sense. I figure the computer triggered a fault routine when the switch operation was wonky, which is a good thing. If there was a transmission problem, it's better that the tractor stay stopped than tear itself apart. Remember, there is no feedback to the operator with these electronically controlled units, at least not like with conventional clutches, so by the time the operator heard something, it would be too late.

Next step is to order the part. Pretty sure I need a crush washer too so I'm going to talk to the parts guy on Monday to see what he says. I don't care to take it off now because I'm certain it's going to spill oil out the hole and besides, I have work to do... in gears 3 and 4.

 

[FarmaBro]

All is well again. The new switch did indeed resolve my problem. This happened a few days ago but I thought I'd do a failure analysis of the switch and share my findings.

First I need to say that I am very impressed with the build quality of this part. Between rubber jacket and conformal coating, it's clear a great effort was made to stop the ingress of dirt and moisture. The wires are sleeved and the connector has rubber seals. That made me feel better about paying $150.00 for it.

Upon initial inspection, I found the actuator pin wasn't operating smoothly. Disassembly was simply not possible so I cut it open. Inside I found all the contacts and the slots in which they travel to be in good shape. What did concern me however was the cavity inside was full of transparent goo which I believe was resisting the spring force inside the sealed cavity. I am familiar with silicone grease and I do suspect the contacts were coated prior to assembly given all the other efforts made to produce a reliable part but it sure seemed like there was hydraulic fluid inside as well. It must have leaked past the o-ring that seals the actuator pin against the switch body. I could find no signs of damage on the o-ring and I have a hunch that the ingress occurred while operating in extreme temperatures. I really should have taken photos before throwing it away.

Other things I learned:

1) When troubleshooting a problem, make sure to try as many modes of operation as possible, even if you can't fathom why it would matter. Had I tried gears 3 and 4, the tractor would have operated normally. That wouldn't have just been a hint, it would have let me finish my work.

2) If a controller/computer module is suspect, get a wiring diagram and test operation of all accessory devices that go into and come out of the module right at the module connector. It can yield much information and can save the trouble of disassembly and contortion to access harder to reach areas. What I mean is exposing the connector will give access to the most test areas with the least amount of effort.

The story ends here. I hope that others may benefit from my story as I have benefitted from others.

 

[Ford850]

Thanks for the follow up on this. Too many times we never hear back about an issue and don't know if it was resolved or not. I'm hoping I don't need this fix for my DX55, but I'm glad the solution is here if I need it.

 

[FarmaBro]

The saga continues.

Today I tried to hook up my snowblower but I never got it unburied before the clutch failed to engage. Of course it's in a really inconvenient location and it's raining today. The switch I replaced was not behaving as it should so I'm glad to have replaced it but there is obviously some other problem here.

One new observation is that the clutch seems to engage just fine for a short period of time after the tractor has been sitting for several days.

The next thing to check is the output voltage of the potentiometer. It's resistance seems okay but I have to check voltage in situ which requires I expose a test point. I'll seal it up with a blob of silicone when I'm done.

I'm also considering testing the EHSS control module on using my bench power supply but I'll need to find suitable connectors somewhere.

If anyone has a breakout box (380001351) for this, I'd be interested in buying it. PM me.